chunxi zhang - Academia.edu (original) (raw)
Papers by chunxi zhang
Research Square (Research Square), Dec 25, 2023
The photosynthetic oxygen-evolving center (OEC) is a unique Mn 4 CaO 5-cluster that catalyses the... more The photosynthetic oxygen-evolving center (OEC) is a unique Mn 4 CaO 5-cluster that catalyses the watersplitting reaction in nature. It is a long-standing challenge to precisely mimic the structure and function of the OEC in the laboratory. Herein we report two synthetic Mn 3 Ce 2 O 5-clusters that display unprecedented similarities to the OEC regarding the ten-atom core and the alkyl carboxylate peripheral ligands, as well as the catalytic capability of the water-splitting reaction in aqueous solution. In addition, it has been shown that the oxide bridge in the cluster can rapidly exchange with the isotopic oxygen of H 2 18 O in solution. These results, for the rst time, demonstrate that cerium can structurally and functionally replace both the calcium and one manganese in the cluster. Our data provide chemical evidence that the oxide bridge could be directly involved in the O-O bond formation in its biological paragon and shed new light on the design of water-splitting catalysts in future.
Frontiers in Microbiology, 2019
Our previous investigation of substrates reduction catalyzed by nitrogenase suggested that α-Ile ... more Our previous investigation of substrates reduction catalyzed by nitrogenase suggested that α-Ile 423 of MoFe protein possibly functions as an electron transfer gate to Mo site of active center-"FeMoco". Amino acid residue α-Lys 424 connects directly to α-Ile 423 , and they are located in the same α-helix (α423-431). In the present study, function of α-Lys 424 was investigated by replacing it with Arg (alkaline, like Lys), Gln (neutral), Glu (acidic), and Ala (neutral) through site-directed mutagenesis and homologous recombination. The mutants were, respectively, termed 424R, 424Q, 424E, and 424A. Studies of diazotrophic cell growth, cytological, and enzymatic properties indicated that none of the substitutions altered the secondary structure of MoFe protein, or normal expression of nifA, nifL, and nifD. Substitution of alkaline amino acid (i.e., 424R) maintained acetylene (C 2 H 2) and proton (H +) reduction activities at normal levels similar to that of wild-type (WT), because its FeMoco content did not reduce. In contrast, substitution of acidic or neutral amino acid (i.e., 424Q, 424E, 424A) impaired the catalytic activity of nitrogenase to varying degrees. Combination of MoFe protein structural simulation and the results of a series of experiments, the function of α-Lys 424 in ensuring insertion of FeMoco to MoFe protein was further confirmed, and the contribution of α-Lys 424 in maintaining low potential of the microenvironment causing efficient catalytic activity of nitrogenase was demonstrated.
Catalysts, 2020
The oxygen-evolving center (OEC) in photosystem II (PSII) of plants, algae and cyanobacteria is a... more The oxygen-evolving center (OEC) in photosystem II (PSII) of plants, algae and cyanobacteria is a unique natural catalyst that splits water into electrons, protons and dioxygen. The crystallographic studies of PSII have revealed that the OEC is an asymmetric Mn4CaO5-cluster. The understanding of the structure-function relationship of this natural Mn4CaO5-cluster is impeded mainly due to the complexity of the protein environment and lack of a rational chemical model as a reference. Although it has been a great challenge for chemists to synthesize the OEC in the laboratory, significant advances have been achieved recently. Different artificial complexes have been reported, especially a series of artificial Mn4CaO4-clusters that closely mimic both the geometric and electronic structures of the OEC in PSII, which provides a structurally well-defined chemical model to investigate the structure-function relationship of the natural Mn4CaO5-cluster. The deep investigations on this artificia...
National Science Review, 2017
Dalton Transactions, 2015
Artificial synthetic MnIVCa–oxido complexes containing reactive water molecules have been synthes... more Artificial synthetic MnIVCa–oxido complexes containing reactive water molecules have been synthesized to mimic the oxygen-evolving center in photosystem II.
Science in China Series C: Life Sciences, 2000
The interaction between the Mn-cluster and its peripheral ligands in oxygen-evolving center is st... more The interaction between the Mn-cluster and its peripheral ligands in oxygen-evolving center is still unclear. Theoretical investigation on the coordination of histidine, H 2 O, and Cl to Mn2O2 units in OEC is conducted. The following conclusions are obtained: (i) both histidine and H 2 O molecule, bound to the two Mn ions, respectively, are vertical to the Mn2O2 plane, and maintain a large distance; (ii) the two H 2 O molecules cannot bind to the same Mn2O2 unit. Based on Mn-cluster structure in OEC, we theoretically predict that two H 2 O molecules bind to the two Mn ions at the "C"-shaped open end in S 0 state, while two His residues at the closed end. Cl ion can only terminally ligate at the open end. Individual valence for the four Mn ions in S 0 state is assigned.
Photochemical & Photobiological Sciences, 2007
In this work, the spectral responses of hypocrellin B (HB) to the microenvironments of various bi... more In this work, the spectral responses of hypocrellin B (HB) to the microenvironments of various biomolecules were studied, with human serum albumin (HSA), bovine serum albumin (BSA) and ovalbumin (OVA) used as the models for proteins, sodium alginate (SOA) and hyaluronan (HYA) for polysaccharides and liposomes for lipid membranes. Generally, compared to those in aqueous solution, the absorbance and fluorescence of HB were all strengthened in the model systems except for the fluorescence in HYA. Specially, according to the spectral responses of HB, the microenvironments in biomolecules and liposomes could be set in a sequence of hydrophobic grades, i.e., liposomes > proteins > polysaccharides. Further, R F/A , a parameter defined as the ratio of the fluorescence intensity to the absorbance, was proposed to identify the microenvironment quantitatively. It was found that the R F/A could not only distinguish various types of biomolecules but also identify specific binding from nonspecific binding to proteins or polysaccharides.
Journal of the American Chemical Society, 2007
Intramolecular electron transfer is observed for two new substituted tetrathiafulvalene (TTF)quin... more Intramolecular electron transfer is observed for two new substituted tetrathiafulvalene (TTF)quinone dyads 1 and 2 in the presence of metal ions. On the basis of the electrochemical studies of reference compound 5 and the comparative studies with dyad 3, it was proposed that the synergic coordination of the radical anion of quinone and the oligoethylene glycol chain with metal ions may be responsible for stabilizing the charge-separation state and thus facilitating the electron-transfer process. Most interestingly, the intramolecular electron-transfer processes within these two dyads can be modulated by UV-vis light irradiation in the presence of spiropyran, by taking advantage of its unique properties.
Chinese Science Bulletin, 2013
The detailed structure of catalytic center of water oxidation, Mn 4 Ca-cluster, in photosystem II... more The detailed structure of catalytic center of water oxidation, Mn 4 Ca-cluster, in photosystem II (PSII) has been reported recently. However, due to the radiation damage induced by X-ray and the complexity of the Mn 4 Ca-cluster, the assignment of the 4-O5 atom coordinated by three Mn and one Ca 2+ ions is still lack of essential evidences. In this article, we synthesized one Mn complex containing two 4-O atoms. It is found that the lengths of all 4-O-Mn bonds in this Mn complex are in the range of 1.89-2.10 Å, which are significantly shorter than 2.40-2.61 Å distance of 4-O5-Mn bonds in Mn 4 Ca-cluster observed in the crystal structure of PSII. In addition, DFT calculations have been carried out on the Mn 4 Ca-cluster. It is found that the O atom of 4-O or 4-OH always trends to deviate from the center position of four metal ions, resulting in unequal bond lengths of four 4-O-M (M=Mn or Ca), which is obviously different with larger and nearly equal distances between 4-O and four metal ions observed in the crystal structure. Based on these results, we suggest that the 4-atom in Mn 4 Ca-cluster of PSII is unlikely to be a 4-O, 4-OH or 4-OH 2 , and its assignment is still an open question.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2008
In intact PSII, both the secondary electron donor (Tyr Z) and side-path electron donors (Car/Chl ... more In intact PSII, both the secondary electron donor (Tyr Z) and side-path electron donors (Car/Chl Z /Cyt b559) can be oxidized by P 680 + U at cryogenic temperatures. In this paper, the effects of acceptor side, especially the redox state of the non-heme iron, on the donor side electron transfer induced by visible light at cryogenic temperatures were studied by EPR spectroscopy. We found that the formation and decay of the S 1 Tyr Z U EPR signal were independent of the treatment of K 3 Fe(CN) 6 , whereas formation and decay of the Car + U /Chl Z + U EPR signal correlated with the reduction and recovery of the Fe 3+ EPR signal of the non-heme iron in K 3 Fe(CN) 6 pre-treated PSII, respectively. Based on the observed correlation between Car/Chl Z oxidation and Fe 3+ reduction, the oxidation of non-heme iron by K 3 Fe(CN) 6 at 0°C was quantified, which showed that around 50-60% fractions of the reaction centers gave rise to the Fe 3+ EPR signal. In addition, we found that the presence of phenyl-p-benzoquinone significantly enhanced the yield of Tyr Z oxidation. These results indicate that the electron transfer at the donor side can be significantly modified by changes at the acceptor side, and indicate that two types of reaction centers are present in intact PSII, namely, one contains unoxidizable nonheme iron and another one contains oxidizable non-heme iron. Tyr Z oxidation and side-path reaction occur separately in these two types of reaction centers, instead of competition with each other in the same reaction centers. In addition, our results show that the non-heme iron has different properties in active and inactive PSII. The oxidation of non-heme iron by K 3 Fe(CN) 6 takes place only in inactive PSII, which implies that the Fe 3+ state is probably not the intermediate species for the turnover of quinone reduction.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2006
In the field of photosynthetic water oxidation it has been under debate whether Tyrosine Z (Tyr Z... more In the field of photosynthetic water oxidation it has been under debate whether Tyrosine Z (Tyr Z) acts as a hydrogen or an electron acceptor from water. In the former concept, direct contact of Tyr Z with substrate water has been assumed. However, there is no direct evidence for the interaction between Tyr Z and substrate water in active Photosystem II (PSII), instead most experiments have been performed on inhibited PSII. Here, this problem is tackled in active PSII by combining low temperature EPR measurements and quantum chemistry calculations. EPR measurements observed that the maximum yield of Tyr Z oxidation at cryogenic temperature in the S 0 and S 1 states was around neutral pH and was essentially pHindependent. The yield of Tyr Z oxidation decreased at acidic and alkaline pH, with pKs at 4.7-4.9 and 7.7, respectively. The observed pH-dependent parts at low and high values of pH can be explained as due to sample inactivation, rather than active PSII. The reduction kinetics of Tyr Z • in the S 0 and S 1 states were pH independent at pH range from 4.5 to 8. Therefore, the change of the pH in bulk solution probably has no effect on the Tyr Z oxidation and Tyr Z • reduction at cryogenic temperature in the S 0 and S 1 states of the active PSII. Theoretical calculations indicate that Tyr Z becomes more difficult to oxidize when a H 2 O molecule interacts directly with it. It is suggested that Tyr Z is probably located in a hydrophobic environment with no direct interaction with the substrate H 2 O in active PSII. These results provide new insights on the function and mechanism of water oxidation in PSII.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2010
The correlation between the reduction of Q A and the oxidation of Tyr Z or Car/Chl Z /Cyt b559 in... more The correlation between the reduction of Q A and the oxidation of Tyr Z or Car/Chl Z /Cyt b559 in spinach PSII enriched membranes induced by visible light at 10 K is studied by using electron paramagnetic resonance spectroscopy. Similar g = 1.95-1.86 Q A-• EPR signals are observed in both Mn-depleted and intact samples, and both signals are long lived at low temperatures. The presence of PPBQ significantly diminished the light induced EPR signals from Q A-• , Car +• /Chl +• and oxidized Cyt b559 , while enhancing the amplitude of the S 1 Tyr Z • EPR signal in the intact PSII sample. The quantification and stability of the g = 1.95-1.86 EPR signal and signals arising from the oxidized Tyr Z and the side-path electron donors, respectively, indicate that the EPR-detectable g = 1.95-1.86 Q A-• signal is only correlated to reaction centers undergoing oxidation of the side-path electron donors (Car/Chl Z /Cyt b559), but not of Tyr Z. These results imply that two types of Q A-• probably exist in the intact PSII sample. The structural difference and possible function of the two types of Q A are discussed.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2010
Chloride is an essential cofactor for photosynthetic water oxidation. However, its location and f... more Chloride is an essential cofactor for photosynthetic water oxidation. However, its location and functional roles in active photosystem II are still a matter of debate. We have investigated this issue by studying the effects of Cl − replacement by Br − in active PSII. In Br − substituted samples, Cl − is effectively replaced by Br − in the presence of 1.2 M NaBr under room light with protection of anaerobic atmosphere followed by dialysis. The following results have been obtained. i) The oxygen-evolving activities of the Br −-PSII samples are significantly lower than that of the Cl −-PSII samples; ii) The same S 2 multiline EPR signals are observed in both Br − and Cl −-PSII samples; iii) The amplitudes of the visible light induced S 1 Tyr Z • and S 2 Tyr Z • EPR signals are significantly decreased after Br − substitution; the S 1 Tyr Z • EPR signal is up-shifted about 8 G, whereas the S 2 Tyr Z • signal is down-shifted about 12 G after Br − substitution. These results imply that the redox properties of Tyr Z and spin interactions between Tyr Z • and Mn-cluster could be significantly modified due to Br − substitution. It is suggested that Cl − /Br − probably coordinates to the Ca 2+ ion of the Mn-cluster in active photosystem II.
Science China. Life sciences, Jan 6, 2015
T. New structure model of oxygen-evolving center and mechanism for oxygen evolution in photosynth... more T. New structure model of oxygen-evolving center and mechanism for oxygen evolution in photosynthesis. Chin Sci Bull, 1999, 44: 22092215 6 Zhang C, Low-barrier hydrogen bond plays key role in active photosystem II-a new model for photosynthetic water oxidation. Biochim Biophys Acta, 2007, 1767: 493499 7 Ren Y, Zhang C, Zhao J. Substitution of chloride by bromide modifies the low-temperature tyrosine z oxidation in active photosystem II.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2007
The function and mechanism of Tyr Z in active photosystem II (PSII) is one of the long-standing i... more The function and mechanism of Tyr Z in active photosystem II (PSII) is one of the long-standing issues in the study of photosynthetic water oxidation. Based on recent investigations on active PSII and theoretical studies, a new model is proposed, in which D1-His190 acts as a bridge, to form a low-barrier hydrogen bond (LBHB) with Tyr Z , and a coordination bond to Mn or Ca ion of the Mn-cluster. Accordingly, this new model differs from previous proposals concerning the mechanism of Tyr Z function in two aspects. First, the LBHB plays a key role to decrease the activation energy for Tyr Z oxidation and Tyr Z • reduction during photosynthetic water oxidation. Upon the oxidation of Tyr Z , the hydrogen bond between Tyr Z and His190 changes from a LBHB to a weak hydrogen bond, and vice versa upon Tyr Z • reduction. In both stages, the electron transfer and proton transfer are coupled. Second, the positive charge formed after Tyr Z oxidation may play an important role for water oxidation. It can be delocalized on the Mn-cluster, thus helps to accelerate the proton release from substrate water on Mn-cluster. This model is well reconciled with observations of the S-state dependence of Tyr Z oxidation and Tyr Z • reduction, proton release, isotopic effect and recent EPR experiments. Moreover, the difference between Tyr Z and Tyr D in active PSII can also be readily rationalized. The His190 binding to the Mn-cluster predicted in this model is contradictious to the recent structure data, however, it has been aware that the crystal structure of the Mn-cluster and its environment are significantly modified by X-ray due to radiation damage and are different from that in active PSII. It is suggested that the His190 may be protonated during the radiation damage, which leads to the loss of its binding to Mn-cluster and the strong hydrogen bond with Tyr Z. This type of change arising from radiation damage has been confirmed in other enzyme systems.
Chemical Communications, 2014
An artificial complex containing Mn3SrO4 and three types of μ-O2− moieties has been synthesized t... more An artificial complex containing Mn3SrO4 and three types of μ-O2− moieties has been synthesized to mimic the OEC in PSII.
By using the in situ IR spectroscopy, the superoxide species (O 2-), characterized by the O-O str... more By using the in situ IR spectroscopy, the superoxide species (O 2-), characterized by the O-O stretching peak at 1130 cm-1 , was detected on the SrF 2 / La 2 O 3 catalyst at temperatures up to 973 K. The introduction of 18 O 2 isotope caused the 1130 cm-1 peak to shift to lower wavenumbers (1095 and 1064 cm-1), consistent with the assignment of the spectra to the superoxide species. A good correlation between the rate of the disappearance of the O 2 species and that of the formation of C 2 H 4 was observed, suggesting that O 2 was the active oxygen species responsible for the oxidative coupling of methane (OCM) on the SrF 2 /La 2 O 3 catalyst. This conclusion was reinforced by the EPR experiments (g xx = 2.0001, g yy = 2.0045, g zz = 2.0685), showing that O 2 was the only paramagnetic oxygen species detectable on the O 2-preadsorbed SrF 2 /La 2 O 3 catalyst. These results suggest that superoxide O 2 can be a stable active oxygen species, whose role in the OCM reaction cannot be overlooked.
In Synechocystis sp. PCC 6803, the loop domain (aa 1-70) of the phycobilisome core-membrane linke... more In Synechocystis sp. PCC 6803, the loop domain (aa 1-70) of the phycobilisome core-membrane linker, L(CM), was found to interact with the glycosyl transferase homolog, Sll1466. Growth of a Sll1466 knock-out mutant was slightly faster in low light, but strongly inhibited in high light; the phenotype is discussed in relation to the regulation of light energy transfer to photosystem II. At the molecular level, the mutant shows the following changes compared to the wild type: (1) a smaller size and higher mobility of phycobilisomes on the thylakoid membrane, and (2) a changed lipid composition of the thylakoid membrane, especially decreased amounts of digalactosyl diacylglycerol. These results indicate a profound regulatory role for Sll1466 in regulating photosynthetic energy transfer.
Research Square (Research Square), Dec 25, 2023
The photosynthetic oxygen-evolving center (OEC) is a unique Mn 4 CaO 5-cluster that catalyses the... more The photosynthetic oxygen-evolving center (OEC) is a unique Mn 4 CaO 5-cluster that catalyses the watersplitting reaction in nature. It is a long-standing challenge to precisely mimic the structure and function of the OEC in the laboratory. Herein we report two synthetic Mn 3 Ce 2 O 5-clusters that display unprecedented similarities to the OEC regarding the ten-atom core and the alkyl carboxylate peripheral ligands, as well as the catalytic capability of the water-splitting reaction in aqueous solution. In addition, it has been shown that the oxide bridge in the cluster can rapidly exchange with the isotopic oxygen of H 2 18 O in solution. These results, for the rst time, demonstrate that cerium can structurally and functionally replace both the calcium and one manganese in the cluster. Our data provide chemical evidence that the oxide bridge could be directly involved in the O-O bond formation in its biological paragon and shed new light on the design of water-splitting catalysts in future.
Frontiers in Microbiology, 2019
Our previous investigation of substrates reduction catalyzed by nitrogenase suggested that α-Ile ... more Our previous investigation of substrates reduction catalyzed by nitrogenase suggested that α-Ile 423 of MoFe protein possibly functions as an electron transfer gate to Mo site of active center-"FeMoco". Amino acid residue α-Lys 424 connects directly to α-Ile 423 , and they are located in the same α-helix (α423-431). In the present study, function of α-Lys 424 was investigated by replacing it with Arg (alkaline, like Lys), Gln (neutral), Glu (acidic), and Ala (neutral) through site-directed mutagenesis and homologous recombination. The mutants were, respectively, termed 424R, 424Q, 424E, and 424A. Studies of diazotrophic cell growth, cytological, and enzymatic properties indicated that none of the substitutions altered the secondary structure of MoFe protein, or normal expression of nifA, nifL, and nifD. Substitution of alkaline amino acid (i.e., 424R) maintained acetylene (C 2 H 2) and proton (H +) reduction activities at normal levels similar to that of wild-type (WT), because its FeMoco content did not reduce. In contrast, substitution of acidic or neutral amino acid (i.e., 424Q, 424E, 424A) impaired the catalytic activity of nitrogenase to varying degrees. Combination of MoFe protein structural simulation and the results of a series of experiments, the function of α-Lys 424 in ensuring insertion of FeMoco to MoFe protein was further confirmed, and the contribution of α-Lys 424 in maintaining low potential of the microenvironment causing efficient catalytic activity of nitrogenase was demonstrated.
Catalysts, 2020
The oxygen-evolving center (OEC) in photosystem II (PSII) of plants, algae and cyanobacteria is a... more The oxygen-evolving center (OEC) in photosystem II (PSII) of plants, algae and cyanobacteria is a unique natural catalyst that splits water into electrons, protons and dioxygen. The crystallographic studies of PSII have revealed that the OEC is an asymmetric Mn4CaO5-cluster. The understanding of the structure-function relationship of this natural Mn4CaO5-cluster is impeded mainly due to the complexity of the protein environment and lack of a rational chemical model as a reference. Although it has been a great challenge for chemists to synthesize the OEC in the laboratory, significant advances have been achieved recently. Different artificial complexes have been reported, especially a series of artificial Mn4CaO4-clusters that closely mimic both the geometric and electronic structures of the OEC in PSII, which provides a structurally well-defined chemical model to investigate the structure-function relationship of the natural Mn4CaO5-cluster. The deep investigations on this artificia...
National Science Review, 2017
Dalton Transactions, 2015
Artificial synthetic MnIVCa–oxido complexes containing reactive water molecules have been synthes... more Artificial synthetic MnIVCa–oxido complexes containing reactive water molecules have been synthesized to mimic the oxygen-evolving center in photosystem II.
Science in China Series C: Life Sciences, 2000
The interaction between the Mn-cluster and its peripheral ligands in oxygen-evolving center is st... more The interaction between the Mn-cluster and its peripheral ligands in oxygen-evolving center is still unclear. Theoretical investigation on the coordination of histidine, H 2 O, and Cl to Mn2O2 units in OEC is conducted. The following conclusions are obtained: (i) both histidine and H 2 O molecule, bound to the two Mn ions, respectively, are vertical to the Mn2O2 plane, and maintain a large distance; (ii) the two H 2 O molecules cannot bind to the same Mn2O2 unit. Based on Mn-cluster structure in OEC, we theoretically predict that two H 2 O molecules bind to the two Mn ions at the "C"-shaped open end in S 0 state, while two His residues at the closed end. Cl ion can only terminally ligate at the open end. Individual valence for the four Mn ions in S 0 state is assigned.
Photochemical & Photobiological Sciences, 2007
In this work, the spectral responses of hypocrellin B (HB) to the microenvironments of various bi... more In this work, the spectral responses of hypocrellin B (HB) to the microenvironments of various biomolecules were studied, with human serum albumin (HSA), bovine serum albumin (BSA) and ovalbumin (OVA) used as the models for proteins, sodium alginate (SOA) and hyaluronan (HYA) for polysaccharides and liposomes for lipid membranes. Generally, compared to those in aqueous solution, the absorbance and fluorescence of HB were all strengthened in the model systems except for the fluorescence in HYA. Specially, according to the spectral responses of HB, the microenvironments in biomolecules and liposomes could be set in a sequence of hydrophobic grades, i.e., liposomes > proteins > polysaccharides. Further, R F/A , a parameter defined as the ratio of the fluorescence intensity to the absorbance, was proposed to identify the microenvironment quantitatively. It was found that the R F/A could not only distinguish various types of biomolecules but also identify specific binding from nonspecific binding to proteins or polysaccharides.
Journal of the American Chemical Society, 2007
Intramolecular electron transfer is observed for two new substituted tetrathiafulvalene (TTF)quin... more Intramolecular electron transfer is observed for two new substituted tetrathiafulvalene (TTF)quinone dyads 1 and 2 in the presence of metal ions. On the basis of the electrochemical studies of reference compound 5 and the comparative studies with dyad 3, it was proposed that the synergic coordination of the radical anion of quinone and the oligoethylene glycol chain with metal ions may be responsible for stabilizing the charge-separation state and thus facilitating the electron-transfer process. Most interestingly, the intramolecular electron-transfer processes within these two dyads can be modulated by UV-vis light irradiation in the presence of spiropyran, by taking advantage of its unique properties.
Chinese Science Bulletin, 2013
The detailed structure of catalytic center of water oxidation, Mn 4 Ca-cluster, in photosystem II... more The detailed structure of catalytic center of water oxidation, Mn 4 Ca-cluster, in photosystem II (PSII) has been reported recently. However, due to the radiation damage induced by X-ray and the complexity of the Mn 4 Ca-cluster, the assignment of the 4-O5 atom coordinated by three Mn and one Ca 2+ ions is still lack of essential evidences. In this article, we synthesized one Mn complex containing two 4-O atoms. It is found that the lengths of all 4-O-Mn bonds in this Mn complex are in the range of 1.89-2.10 Å, which are significantly shorter than 2.40-2.61 Å distance of 4-O5-Mn bonds in Mn 4 Ca-cluster observed in the crystal structure of PSII. In addition, DFT calculations have been carried out on the Mn 4 Ca-cluster. It is found that the O atom of 4-O or 4-OH always trends to deviate from the center position of four metal ions, resulting in unequal bond lengths of four 4-O-M (M=Mn or Ca), which is obviously different with larger and nearly equal distances between 4-O and four metal ions observed in the crystal structure. Based on these results, we suggest that the 4-atom in Mn 4 Ca-cluster of PSII is unlikely to be a 4-O, 4-OH or 4-OH 2 , and its assignment is still an open question.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2008
In intact PSII, both the secondary electron donor (Tyr Z) and side-path electron donors (Car/Chl ... more In intact PSII, both the secondary electron donor (Tyr Z) and side-path electron donors (Car/Chl Z /Cyt b559) can be oxidized by P 680 + U at cryogenic temperatures. In this paper, the effects of acceptor side, especially the redox state of the non-heme iron, on the donor side electron transfer induced by visible light at cryogenic temperatures were studied by EPR spectroscopy. We found that the formation and decay of the S 1 Tyr Z U EPR signal were independent of the treatment of K 3 Fe(CN) 6 , whereas formation and decay of the Car + U /Chl Z + U EPR signal correlated with the reduction and recovery of the Fe 3+ EPR signal of the non-heme iron in K 3 Fe(CN) 6 pre-treated PSII, respectively. Based on the observed correlation between Car/Chl Z oxidation and Fe 3+ reduction, the oxidation of non-heme iron by K 3 Fe(CN) 6 at 0°C was quantified, which showed that around 50-60% fractions of the reaction centers gave rise to the Fe 3+ EPR signal. In addition, we found that the presence of phenyl-p-benzoquinone significantly enhanced the yield of Tyr Z oxidation. These results indicate that the electron transfer at the donor side can be significantly modified by changes at the acceptor side, and indicate that two types of reaction centers are present in intact PSII, namely, one contains unoxidizable nonheme iron and another one contains oxidizable non-heme iron. Tyr Z oxidation and side-path reaction occur separately in these two types of reaction centers, instead of competition with each other in the same reaction centers. In addition, our results show that the non-heme iron has different properties in active and inactive PSII. The oxidation of non-heme iron by K 3 Fe(CN) 6 takes place only in inactive PSII, which implies that the Fe 3+ state is probably not the intermediate species for the turnover of quinone reduction.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2006
In the field of photosynthetic water oxidation it has been under debate whether Tyrosine Z (Tyr Z... more In the field of photosynthetic water oxidation it has been under debate whether Tyrosine Z (Tyr Z) acts as a hydrogen or an electron acceptor from water. In the former concept, direct contact of Tyr Z with substrate water has been assumed. However, there is no direct evidence for the interaction between Tyr Z and substrate water in active Photosystem II (PSII), instead most experiments have been performed on inhibited PSII. Here, this problem is tackled in active PSII by combining low temperature EPR measurements and quantum chemistry calculations. EPR measurements observed that the maximum yield of Tyr Z oxidation at cryogenic temperature in the S 0 and S 1 states was around neutral pH and was essentially pHindependent. The yield of Tyr Z oxidation decreased at acidic and alkaline pH, with pKs at 4.7-4.9 and 7.7, respectively. The observed pH-dependent parts at low and high values of pH can be explained as due to sample inactivation, rather than active PSII. The reduction kinetics of Tyr Z • in the S 0 and S 1 states were pH independent at pH range from 4.5 to 8. Therefore, the change of the pH in bulk solution probably has no effect on the Tyr Z oxidation and Tyr Z • reduction at cryogenic temperature in the S 0 and S 1 states of the active PSII. Theoretical calculations indicate that Tyr Z becomes more difficult to oxidize when a H 2 O molecule interacts directly with it. It is suggested that Tyr Z is probably located in a hydrophobic environment with no direct interaction with the substrate H 2 O in active PSII. These results provide new insights on the function and mechanism of water oxidation in PSII.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2010
The correlation between the reduction of Q A and the oxidation of Tyr Z or Car/Chl Z /Cyt b559 in... more The correlation between the reduction of Q A and the oxidation of Tyr Z or Car/Chl Z /Cyt b559 in spinach PSII enriched membranes induced by visible light at 10 K is studied by using electron paramagnetic resonance spectroscopy. Similar g = 1.95-1.86 Q A-• EPR signals are observed in both Mn-depleted and intact samples, and both signals are long lived at low temperatures. The presence of PPBQ significantly diminished the light induced EPR signals from Q A-• , Car +• /Chl +• and oxidized Cyt b559 , while enhancing the amplitude of the S 1 Tyr Z • EPR signal in the intact PSII sample. The quantification and stability of the g = 1.95-1.86 EPR signal and signals arising from the oxidized Tyr Z and the side-path electron donors, respectively, indicate that the EPR-detectable g = 1.95-1.86 Q A-• signal is only correlated to reaction centers undergoing oxidation of the side-path electron donors (Car/Chl Z /Cyt b559), but not of Tyr Z. These results imply that two types of Q A-• probably exist in the intact PSII sample. The structural difference and possible function of the two types of Q A are discussed.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2010
Chloride is an essential cofactor for photosynthetic water oxidation. However, its location and f... more Chloride is an essential cofactor for photosynthetic water oxidation. However, its location and functional roles in active photosystem II are still a matter of debate. We have investigated this issue by studying the effects of Cl − replacement by Br − in active PSII. In Br − substituted samples, Cl − is effectively replaced by Br − in the presence of 1.2 M NaBr under room light with protection of anaerobic atmosphere followed by dialysis. The following results have been obtained. i) The oxygen-evolving activities of the Br −-PSII samples are significantly lower than that of the Cl −-PSII samples; ii) The same S 2 multiline EPR signals are observed in both Br − and Cl −-PSII samples; iii) The amplitudes of the visible light induced S 1 Tyr Z • and S 2 Tyr Z • EPR signals are significantly decreased after Br − substitution; the S 1 Tyr Z • EPR signal is up-shifted about 8 G, whereas the S 2 Tyr Z • signal is down-shifted about 12 G after Br − substitution. These results imply that the redox properties of Tyr Z and spin interactions between Tyr Z • and Mn-cluster could be significantly modified due to Br − substitution. It is suggested that Cl − /Br − probably coordinates to the Ca 2+ ion of the Mn-cluster in active photosystem II.
Science China. Life sciences, Jan 6, 2015
T. New structure model of oxygen-evolving center and mechanism for oxygen evolution in photosynth... more T. New structure model of oxygen-evolving center and mechanism for oxygen evolution in photosynthesis. Chin Sci Bull, 1999, 44: 22092215 6 Zhang C, Low-barrier hydrogen bond plays key role in active photosystem II-a new model for photosynthetic water oxidation. Biochim Biophys Acta, 2007, 1767: 493499 7 Ren Y, Zhang C, Zhao J. Substitution of chloride by bromide modifies the low-temperature tyrosine z oxidation in active photosystem II.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2007
The function and mechanism of Tyr Z in active photosystem II (PSII) is one of the long-standing i... more The function and mechanism of Tyr Z in active photosystem II (PSII) is one of the long-standing issues in the study of photosynthetic water oxidation. Based on recent investigations on active PSII and theoretical studies, a new model is proposed, in which D1-His190 acts as a bridge, to form a low-barrier hydrogen bond (LBHB) with Tyr Z , and a coordination bond to Mn or Ca ion of the Mn-cluster. Accordingly, this new model differs from previous proposals concerning the mechanism of Tyr Z function in two aspects. First, the LBHB plays a key role to decrease the activation energy for Tyr Z oxidation and Tyr Z • reduction during photosynthetic water oxidation. Upon the oxidation of Tyr Z , the hydrogen bond between Tyr Z and His190 changes from a LBHB to a weak hydrogen bond, and vice versa upon Tyr Z • reduction. In both stages, the electron transfer and proton transfer are coupled. Second, the positive charge formed after Tyr Z oxidation may play an important role for water oxidation. It can be delocalized on the Mn-cluster, thus helps to accelerate the proton release from substrate water on Mn-cluster. This model is well reconciled with observations of the S-state dependence of Tyr Z oxidation and Tyr Z • reduction, proton release, isotopic effect and recent EPR experiments. Moreover, the difference between Tyr Z and Tyr D in active PSII can also be readily rationalized. The His190 binding to the Mn-cluster predicted in this model is contradictious to the recent structure data, however, it has been aware that the crystal structure of the Mn-cluster and its environment are significantly modified by X-ray due to radiation damage and are different from that in active PSII. It is suggested that the His190 may be protonated during the radiation damage, which leads to the loss of its binding to Mn-cluster and the strong hydrogen bond with Tyr Z. This type of change arising from radiation damage has been confirmed in other enzyme systems.
Chemical Communications, 2014
An artificial complex containing Mn3SrO4 and three types of μ-O2− moieties has been synthesized t... more An artificial complex containing Mn3SrO4 and three types of μ-O2− moieties has been synthesized to mimic the OEC in PSII.
By using the in situ IR spectroscopy, the superoxide species (O 2-), characterized by the O-O str... more By using the in situ IR spectroscopy, the superoxide species (O 2-), characterized by the O-O stretching peak at 1130 cm-1 , was detected on the SrF 2 / La 2 O 3 catalyst at temperatures up to 973 K. The introduction of 18 O 2 isotope caused the 1130 cm-1 peak to shift to lower wavenumbers (1095 and 1064 cm-1), consistent with the assignment of the spectra to the superoxide species. A good correlation between the rate of the disappearance of the O 2 species and that of the formation of C 2 H 4 was observed, suggesting that O 2 was the active oxygen species responsible for the oxidative coupling of methane (OCM) on the SrF 2 /La 2 O 3 catalyst. This conclusion was reinforced by the EPR experiments (g xx = 2.0001, g yy = 2.0045, g zz = 2.0685), showing that O 2 was the only paramagnetic oxygen species detectable on the O 2-preadsorbed SrF 2 /La 2 O 3 catalyst. These results suggest that superoxide O 2 can be a stable active oxygen species, whose role in the OCM reaction cannot be overlooked.
In Synechocystis sp. PCC 6803, the loop domain (aa 1-70) of the phycobilisome core-membrane linke... more In Synechocystis sp. PCC 6803, the loop domain (aa 1-70) of the phycobilisome core-membrane linker, L(CM), was found to interact with the glycosyl transferase homolog, Sll1466. Growth of a Sll1466 knock-out mutant was slightly faster in low light, but strongly inhibited in high light; the phenotype is discussed in relation to the regulation of light energy transfer to photosystem II. At the molecular level, the mutant shows the following changes compared to the wild type: (1) a smaller size and higher mobility of phycobilisomes on the thylakoid membrane, and (2) a changed lipid composition of the thylakoid membrane, especially decreased amounts of digalactosyl diacylglycerol. These results indicate a profound regulatory role for Sll1466 in regulating photosynthetic energy transfer.