Cytochrome c 6-like protein as a putative donor of electrons to photosystem I in the cyanobacterium Nostoc sp. PCC 7119

Abstract

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or plastocyanin, or both, to transfer electrons from cytochrome b(6)-f to photosystem I. Even though plastocyanin has superseded cytochrome c(6) along evolution, plants contain a modified cytochrome c(6), the so called cytochrome c(6A), whose function still remains unknown.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) and plastocyanin. In any way, the Cyt c(6)-like protein from Nostoc sp. PCC 7119 would be potentially utilized for the biohydrogen production, using cell-free photosystem I catalytic nanoparticles.

Insights into the relationship between the haem-binding pocket and the redox potential ofc6cytochromes: four atomic resolution structures ofc6andc6-like proteins fromSynechococcussp. PCC 7002

“…The most important difference lies in the east face, which is heavily negatively charged in cyt c 6C . As this is the only available structure of cyt c 6C to date, there are no other available data about surface charge distribution in proteins of this type apart from the theoretical calculations of Reyes-Sosa et al (2011). Their data suggest that other cyt c 6 -like proteins from nitrogen-fixing cyanobacteria have a similar negative patch.…”

“…Recently, a cyt c 6 -like protein from Nostoc sp. PCC 7119 was characterized to some extent by Reyes-Sosa et al (2011).…”

“…On the other hand, it has recently been shown that cyt c 6C from Nostoc sp. PCC 7119 can reduce photosystem I, although not as efficiently as cyt c 6 and plastocyanin (Reyes-Sosa et al, 2011).…”

Cytc6-3: A New Isoform of Photosynthetic Cytc6Exclusive to Heterocyst-Forming Cyanobacteria

“…However, it remains unclear whether all these processes involve one or (Ki 2005). In numerous cyanobacteria at least two genes that could encode two Cyt c 6 isoforms have been found (Ki 2005, Bialek et al 2008, Reyes-Sosa et al 2011. One of these isoforms is the genuine petJ gene, which encodes for Cyt c 6 , and the other one encodes a Cyt c 6 -like protein (herein after Cyt c 6-2 ), which cannot oxidize Cyt b 6 f complex but can reduce, although with low efficiency, PSI (Reyes-Sosa et al 2011).…”

“…In numerous cyanobacteria at least two genes that could encode two Cyt c 6 isoforms have been found (Ki 2005, Bialek et al 2008, Reyes-Sosa et al 2011. One of these isoforms is the genuine petJ gene, which encodes for Cyt c 6 , and the other one encodes a Cyt c 6 -like protein (herein after Cyt c 6-2 ), which cannot oxidize Cyt b 6 f complex but can reduce, although with low efficiency, PSI (Reyes-Sosa et al 2011). Also, Bialek et al (2008) described previously two well-defined groups of cyanobacterial Cyt c 6-2 proteins, the Cyt c 6B and the Cyt c 6C , that not appear to be present simultaneously in the same cyanobacterium (Ki 2005).…”