Dynamics of the cyanobacterial photosynthetic network: Communication and modification of membrane protein complexes (original) (raw)
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The PsbQ Protein Defines Cyanobacterial Photosystem II Complexes with Highest Activity and Stability
Proceedings of The National Academy of Sciences, 2007
Light-induced conversion of water to molecular oxygen by Photosystem II (PSII) is one of the most important enzymatic reactions in the biosphere. PSII is a multisubunit membrane protein complex with numerous associated cofactors, but it continually undergoes assembly and disassembly due to frequent light-mediated damage as a result of its normal function. Thus, at any instant, there is heterogeneity in the subunit compositions of PSII complexes within the cell. In particular, cyanobacterial PSII complexes have five associated extrinsic proteins, PsbO, PsbP, PsbQ, PsbU, and PsbV. However, little is known about the interactions of the more recently identified PsbQ protein with other components in cyanobacterial PSII. Here we show that PSII complexes can be isolated from the cyanobacterium Synechocystis sp. PCC 6803 on the basis of the presence of a polyhistidine-tagged PsbQ protein. Purification of PSII complexes using a tagged extrinsic protein has not been previously described, and this work conclusively demonstrates that PsbQ is present in combination with the PsbO, PsbU, and PsbV proteins in cyanobacterial PSII. Moreover, PsbQ-associated PSII complexes have higher activity and stability relative to those isolated using histidine-tagged CP47, an integral membrane protein. Therefore, we conclude that the presence of PsbQ defines the fully assembled and optimally active form of the enzyme. membrane protein complex ͉ oxygen evolution ͉ photosynthesis ͉ synechocystis ‡ To whom correspondence should be addressed.
Higher Plant and Cyanobacterial Photosystem I: Connected Cytochrome Pathways
2016
Oxygenic photosynthesis is the principal converter of sunlight into chemical energy on earth. The conversion of solar energy is catalyzed by four multi-subunit membrane protein complexes: photosystem I (PSI), photosystem II (PSII), the cytochrome b6-f complex (cytb6f) and ATP-synthase (FOF1). These protein complexes are connected by soluble electron carriers that are vital not only for the proper function of ATP and NADPH production but also to render the system highly efficient in different organisms and various environments, some of which are quite harsh. While the main fabric of the membrane complexes is highly conserved, their surfaces and interaction with the soluble factors provide the specificity and fine regulation of the operating system. One of the prime examples for this phenomenon is the cyanobacterial photosynthetic electron transport chain that is situated alongside with respiratory complexes, yet it stays unique by virtue of the interacting soluble components. Cyanoba...
Journal of Biological Chemistry, 1999
Photosystem I (PSI) interacts with plastocyanin or cytochrome c 6 on the luminal side. To identify sites of interaction between plastocyanin/cytochrome c 6 and the PSI core, site-directed mutations were generated in the luminal J loop of the PsaB protein from Synechocystis sp. PCC 6803. The eight mutant strains differed in their photoautotrophic growth. Western blotting with subunit-specific antibodies indicated that the mutations affected the PSI level in the thylakoid membranes. PSI proteins could not be detected in the S600R/G601C/ N602I, N609K/S610C/T611I, and M614I/G615C/W616A mutant membranes. The other mutant strains contained different levels of PSI proteins. Among the mutant strains that contained PSI proteins, the H595C/L596I, Q627H/L628C/I629S, and N638C/N639S mutants showed similar levels of PSI-mediated electron transfer activity when either cytochrome c 6 or an artificial electron donor was used. In contrast, cytochrome c 6 could not function as an electron donor to the W622C/A623R mutant, even though the PSI activity mediated by an artificial electron donor was detected in this mutant. Thus, the W622C/A623R mutation affected the interaction of the PSI complex with cytochrome c 6 . Biotin-maleimide modification of the mutant PSI complexes indicated that His-595, Trp-622, Leu-628, Tyr-632, and Asn-638 in wildtype PsaB may be exposed on the surface of the PSI complex. The results presented here demonstrate the role of an extramembrane loop of a PSI core protein in the interaction with soluble electron donor proteins.
Photosynth Res, 1999
Photosystem I (PSI) interacts with plastocyanin or cytochrome c 6 on the luminal side. To identify sites of interaction between plastocyanin/cytochrome c 6 and the PSI core, site-directed mutations were generated in the luminal J loop of the PsaB protein from Synechocystis sp. PCC 6803. The eight mutant strains differed in their photoautotrophic growth. Western blotting with subunit-specific antibodies indicated that the mutations affected the PSI level in the thylakoid membranes. PSI proteins could not be detected in the S600R/G601C/ N602I, N609K/S610C/T611I, and M614I/G615C/W616A mutant membranes. The other mutant strains contained different levels of PSI proteins. Among the mutant strains that contained PSI proteins, the H595C/L596I, Q627H/L628C/I629S, and N638C/N639S mutants showed similar levels of PSI-mediated electron transfer activity when either cytochrome c 6 or an artificial electron donor was used. In contrast, cytochrome c 6 could not function as an electron donor to the W622C/A623R mutant, even though the PSI activity mediated by an artificial electron donor was detected in this mutant. Thus, the W622C/A623R mutation affected the interaction of the PSI complex with cytochrome c 6 . Biotin-maleimide modification of the mutant PSI complexes indicated that His-595, Trp-622, Leu-628, Tyr-632, and Asn-638 in wildtype PsaB may be exposed on the surface of the PSI complex. The results presented here demonstrate the role of an extramembrane loop of a PSI core protein in the interaction with soluble electron donor proteins.
Proteins of the cyanobacterial photosystem I
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2001
Cyanobacterial photosystem (PS) I is remarkably similar to its counterpart in the chloroplast of plants and algae. Therefore, it has served as a prototype for the type I reaction centers of photosynthesis. Cyanobacterial PS I contains 11^12 proteins. Some of the cyanobacterial proteins are modified post-translationally. Reverse genetics has been used to generate subunit-deficient cyanobacterial mutants, phenotypes of which have revealed the functions of the missing proteins. The cyanobacterial PS I proteins bind cofactors, provide docking sites for electron transfer proteins, participate in tertiary and quaternary organization of the complex and protect the electron transfer centers. Many of these mutants are now being used in sophisticated structure^function analyses. Yet, the roles of some proteins of the cyanobacterial PS I are unknown. It is necessary to examine functions of these proteins on a global scale of cell physiology, biogenesis and evolution. ß 2001 Published by Elsevier Science B.V.
Cyanobacterial Photosystem I lacks specificity in its interaction with cytochrome c6 electron donors
Photosynthesis Research, 2005
In cyanobacteria, plastocyanin and cytochrome c 6 , the alternate donor proteins to Photosystem I, can be acidic, neutral or basic; the role of electrostatics in their interaction with photosystem I varies accordingly. In order to elucidate whether these changes in the electron donors' properties correlate with complementary changes in the docking site of the corresponding photosystem, we have investigated the kinetics of reactions between three cytochrome c 6 with isoelectric points of 5.6, 7.0 and 9.0, with Photosystem I particles from the same three genera of cyanobacteria which provided the cytochromes. The model systems compared here thus sample the full range of charge properties observed in cytochromes c 6 : acidic, basic and neutral. The rate constants and dependence on ionic strength for photosystem I reduction were distinctive for each cytochrome c 6 , but independent of Photosystem I. We conclude that the specific structural features of each cytochrome c 6 dictate their different kinetic behaviours, whereas the three photosystems are relatively indiscriminate in docking with the electron donors.
Biochimica Et Biophysica Acta-bioenergetics, 2009
The cytochrome b 6 f complex is an integral part of the photosynthetic and respiratory electron transfer chain of oxygenic photosynthetic bacteria. The core of this complex is composed of four subunits, cytochrome b, cytochrome f, subunit IV and the Rieske protein (PetC). In this study deletion mutants of all three petC genes of Synechocystis sp. PCC 6803 were constructed to investigate their localization, involvement in electron transfer, respiration and photohydrogen evolution. Immunoblots revealed that PetC1, PetC2, and all other core subunits were exclusively localized in the thylakoids, while the third Rieske protein (PetC3) was the only subunit found in the cytoplasmic membrane. Deletion of petC3 and both of the quinol oxidases failed to elicit a change in respiration rate, when compared to the respective oxidase mutant. This supports a different function of PetC3 other than respiratory electron transfer. We conclude that the cytoplasmic membrane of Synechocystis lacks both a cytochrome c oxidase and the cytochrome b 6 f complex and present a model for the major electron transfer pathways in the two membranes of Synechocystis. In this model there is no proton pumping electron transfer complex in the cytoplasmic membrane. Cyclic electron transfer was impaired in all petC1 mutants. Nonetheless, hydrogenase activity and photohydrogen evolution of all mutants were similar to wild type cells. A reduced linear electron transfer and an increased quinol oxidase activity seem to counteract an increased hydrogen evolution in this case. This adds further support to the close interplay between the cytochrome bd oxidase and the bidirectional hydrogenase.
European Journal of Biochemistry, 1995
Photosystem I and I1 core complexes were resolved in a single step from the thylakoid menibrane of Synechot.y.rti.v sp. PCC 6803 by using a mild solubilization procedure in dodecyl /~-t)-maltoside arid Deriphat/PAGE. For each photosystem, two green bands were obtained containing oligomcric and monomeric forms of the core complexes of either photosystem. The oligoniers are likcly to be trimei-s i n the case of photosystem T and dinicrs for photosystem 11, The absorption spectra, polypeptide and pigment composition of green bands corresponding to cither photosystem I or photosyslem TI wci-e identical for monomeric and oligomeric forms. Thc cytochromc b-559 content of photosystem I1 was evalualed to bc one cytochrome h-S59/reaction centre both in the monomeric and diineric forms. Two new I5-kDa and 22-kDa carotenoid-binding proteins were isolated and their polypeptides purified to homogeneity. Keywords: photosystem I ; photosystem 11; pigment-protein complexes: cyanobacteria.