A comparative structural and functional analysis of cyanobacterial plastocyanin and cytochrome c6 as alternative electron donors to Photosystem I: Photosystem I reduction in cyanobacteria (original) (raw)
Related papers
Journal of Biological Chemistry, 2003
In cyanobacteria, cytochrome c 6 and plastocyanin are able to replace each other as redox carriers in the photosynthetic and respiratory electron transport chains with the synthesis of one or another protein being regulated by the copper concentration in the culture medium. However, the presence of a third unidentified electron carrier has been suggested. To address this point, we have constructed two deletion mutants of the cyanobacterium Synechocystis sp. PCC 6803, each variant lacking either the petE or petJ gene, which respectively codes for the copper or heme protein. The photoautotrophic and heterotrophic growth rate of the two mutants in copper-free and copper-supplemented medium as well as their photosystem I reduction kinetics in vivo were compared with those of wild-type cells. The two mutant strains grow at equivalent rates and show similar in vivo photosystem I reduction kinetics as wildtype cells when cultured in media that allow the expression of just one of the two electron donor proteins, but their ability to grow and reduce photosystem I is much lower when neither cytochrome c 6 nor plastocyanin is expressed. These findings indicate that the normal functioning of the cyanobacterial photosynthetic and respiratory chains obligatorily depends on the presence of either cytochrome c 6 or plastocyanin.
Febs Letters, 2002
Cytochrome cM is a new c-class photosynthetic haem protein whose physiological role is still unknown. It has been proposed previously that cytochrome cM can replace cytochrome c6 and plastocyanin in transferring electrons between the two membrane complexes cytochrome b6–f and photosystem I in organisms growing under stress conditions. The experimental evidence herein provided allows us to discard such a hypothesis. We report a procedure to overexpress cytochrome cM from the cyanobacterium Synechocystis sp. PCC 6803 in Escherichia coli cells in mg quantities. This has allowed us to perform a comparative laser flash-induced kinetic analysis of photosystem I reduction by the three metalloproteins from Synechocystis. The bimolecular rate constant for the overall reaction is up to 100 times lower with cytochrome cM than with cytochrome c6 or plastocyanin. In addition, the redox potential value and surface electrostatic potential distribution of cytochrome cM are quite different from those of cytochrome c6 and plastocyanin. These findings strongly indicate that cytochrome cM cannot be recognised by and interact with the same redox partners as the other two metalloproteins.
Photosynthesis research, 2011
Most organisms performing oxygenic photosynthesis contain either cytochrome c(6) or plastocyanin, or both, to transfer electrons from cytochrome b(6)-f to photosystem I. Even though plastocyanin has superseded cytochrome c(6) along evolution, plants contain a modified cytochrome c(6), the so called cytochrome c(6A), whose function still remains unknown. In this article, we describe a second cytochrome c(6) (the so called cytochrome c(6)-like protein), which is found in some cyanobacteria but is phylogenetically more related to plant cytochrome c(6A) than to cyanobacterial cytochrome c(6). In this article, we conclude that the cytochrome c(6)-like protein is a putative electron donor to photosystem I, but does play a role different to that of cytochrome c(6) and plastocyanin as it cannot accept electrons from cytochrome f. The existence of this third electron donor to PSI could explain why some cyanobacteria are able to grow photoautotrophically in the absence of both cytochrome c(6)...
Site-directed Mutagenesis of Cytochromec 6 from Synechocystissp. PCC 6803
Journal of Biological Chemistry, 1999
This paper reports the first site-directed mutagenesis analysis of any cytochrome c 6 , a heme protein that performs the same function as the copper-protein plastocyanin in the electron transport chain of photosynthetic organisms. Photosystem I reduction by the mutants of cytochrome c 6 from the cyanobacterium Synechocystis sp. PCC 6803 has been studied by laser flash absorption spectroscopy. Their kinetic efficiency and thermodynamic properties have been compared with those of plastocyanin mutants from the same organism. Such a comparative study reveals that aspartates at positions 70 and 72 in cytochrome c 6 are located in an acidic patch that may be isofunctional with the well known "southeast" patch of plastocyanin. Calculations of surface electrostatic potential distribution in the mutants of cytochrome c 6 and plastocyanin indicate that the changes in protein reactivity depend on the surface electrostatic potential pattern rather than on the net charge modification induced by mutagenesis. Phe-64, which is close to the heme group and may be the counterpart of Tyr-83 in plastocyanin, does not appear to be involved in the electron transfer to photosystem I. In contrast, Arg-67, which is at the edge of the cytochrome c 6 acidic area, seems to be crucial for the interaction with the reaction center. Cytochrome c 6 (Cyt) 1 and plastocyanin (Pc) are soluble metalloproteins, located inside the thylakoid lumen of photosynthetic organisms, that carry electrons from cytochrome b 6 f to photosystem I (PSI), which are both membrane-anchored com
Journal of Biological Chemistry, 1994
The petE gene encoding plastocyanin precursor protein from the cyanobacterium Anabaena PCC 7937 was introduced in the cyanobacterial host strain Synechococcus PCC 7942. The host normally only uses cytochrome cSm as Photosystem I (PS I) donor. The heterologous gene was efficiently expressed using the inducible Escherichia coZi trc promoter. Accumulation of plastocyanin protein depended on the presence of Cu2+. The protein was accurately targeted to the thylakoid lumen, from which it could be isolated in the mature form. Redox difference spectroscopy proved the presence of a Cu2+ ion in the holoenzyme. Isolated heterologous plastocyanin was functional in reconstitution of in vitro electron transfer to PS I. The presence of Anabaena plastocyanin in Synechococcus thylakoid membranes increased PS I electron transfer rate 2.5 times. Analysis of P700 redox and PS 11 fluorescence transients in uiuo showed a faster electron transfer through PS I because of enhanced electron supply in the presence of plastocyanin. In addition, the distribution of electrons between photosynthetic and respiratory electron transfer changed. Plastocyanin preferentially donates electrons to PS I rather than to the respiratory cytochrome-c oxidase complex and is not functionally equivalent to cytochrome c65s.
Journal of Biological Chemistry, 2006
To analyze the function of a protein encoded by the open reading frame ssr2998 in Synechocystis sp. PCC 6803, the corresponding gene was disrupted, and the generated mutant strain was analyzed. Loss of the 7.2-kDa protein severely reduced the growth of Synechocystis, especially under high light conditions, and appeared to impair the function of the cytochrome b6 f complex. This resulted in slower electron donation to cytochrome f and photosystem 1 and, concomitantly, over-reduction of the plastoquinone pool, which in turn had an impact on the photosystem 1 to photosystem 2 stoichiometry and state transition. Furthermore, a 7.2-kDa protein, encoded by the open reading frame ssr2998, was co-isolated with the cytochrome b6 f complex from the cyanobacterium Synechocystis sp. PCC 6803. ssr2998 seems to be structurally and functionally associated with the cytochrome b6 f complex from Synechocystis, and the protein could be involved in regulation of electron transfer processes in Synechocystis sp. PCC 6803.
Biochemistry, 2007
The plastocyanin-cytochrome f complex from Nostoc exhibits relevant structural differences when compared with the homologous complexes from other cyanobacteria and plants, with electrostatic and hydrophobic interactions being differently involved in each case. Here, five negatively charged residues of a recombinant form of cytochrome f from Nostoc have been replaced with either neutral or positively charged residues, and the effects of mutations on the kinetics of electron transfer to wild-type and mutant forms of plastocyanin have been measured by laser flash absorption spectroscopy. Cytochrome f mutants with some negative charges replaced with neutral residues exhibit an apparent electron transfer rate constant with wild-type plastocyanin similar to or slightly higher than that of the wild-type species, whereas the mutants with negative charges replaced with positive residues exhibit a significantly lower reactivity. Taken together, these results indicate that the effects of neutralizing residues at the electrostatically charged patch of cytochrome f are smaller than those previously observed for mutants of plastocyanin, thus suggesting that it is the copper protein which determines the specificity of the electrostatic interaction with the heme protein. Moreover, cross reactions between mutants of both proteins reveal the presence of some short-range specific electrostatic interactions. Our findings also make evident the fact that in Nostoc the main contribution to the electrostatic nature of the complex is provided by the small domain of cytochrome f.
European Journal of Biochemistry, 1978
The interrelation of the copper protein plastocyanin, and a soluble c-type cytochrome, c-552, in photosynthetic electron transport has been studied in the genus Chlamydomonas. With C. reinhardtii the plastocyanin : cytochrome c-552 ratio could be changed from 300: 1 to < 1 : 16 simply by omitting copper from the medium, without any other detectable change. Plastocyanin was indetectable in a second species, C. mundana, for which the cytochrome c-552 level was always very high. The properties of Levine's C. reinhardtii mutant lacking plastocyanin, ac-208, were studied and it was found that the photosynthetic capabilities of a suppressed phenotype and suppressed genotype could be explained by reference to the cytochrome c-552 levels. Both proteins were successfully used in reconstitution experiments with chloroplast fragments. Both showed very fast kinetics for reduction by purified Chlamydomonas cytochromef, but the rate of electron transfer from one to the other was much slower. It is concluded that they constitute an interchangeable pair, and the rationale for this and possible analogies are both discussed.
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.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2000
Relative to ferredoxin :NADP reductase (FNR) from chloroplasts, the comparable enzyme in cyanobacteria contains an additional 9 kDa domain at its amino-terminus. The domain is homologous to the phycocyanin associated linker polypeptide CpcD of the light harvesting phycobilisome antennae. The phenotypic consequences of the genetic removal of this domain from the petH gene, which encodes FNR, have been studied in Synechocystis PCC 6803. The in frame deletion of 75 residues at the amino-terminus, rendered chloroplast length FNR enzyme with normal functionality in linear photosynthetic electron transfer. Salt shock correlated with increased abundance of petH mRNA in the wild-type and mutant alike. The truncation stopped salt stress-inducible increase of Photosystem I-dependent cyclic electron flow. Both photoacoustic determination of the storage of energy from Photosystem I specific far-red light, and the re-reduction kinetics of P700 , suggest lack of function of the truncated FNR in the plastoquinone^cytochrome b 6 f complex reductase step of the PS I-dependent cyclic electron transfer chain. Independent gold-immunodecoration studies and analysis of FNR distribution through activity staining after native polyacrylamide gelelectrophoresis showed that association of FNR with the thylakoid membranes of Synechocystis PCC 6803 requires the presence of the extended amino-terminal domain of the enzyme. The truncated vpetH gene was also transformed into a NAD(P)H dehydrogenase (NDH1) deficient mutant of Synechocystis PCC 6803 (strain M55) (T. Ogawa, Proc. Natl. Acad. Sci. USA 88 (1991) 4275^4279). Phenotypic characterisation of the double mutant supported our conclusion that both the NAD(P)H dehydrogenase complex and FNR contribute independently to the quinone cytochrome b 6 f reductase step in PS I-dependent cyclic electron transfer. The distribution, binding properties and function of FNR in the model cyanobacterium Synechocystis PCC 6803 will be discussed. ß 2000 Elsevier Science B.V. All rights reserved. 0005-2728 / 00 / $^see front matter ß 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 2 8 ( 0 0 ) 0 0 0 7 2 -4 Abbreviations