AUTHOR=Torrado Alejandro , Iniesta-Pallarés Macarena , Velázquez-Campoy Adrián , Álvarez Consolación , Mariscal Vicente , Molina-Heredia Fernando P. 

TITLE=Phylogenetic and functional analysis of cyanobacterial Cytochrome c6-like proteins

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1227492

DOI=10.3389/fpls.2023.1227492

ISSN=1664-462X

ABSTRACT=<p>All known photosynthetic cyanobacteria carry a cytochrome <italic>c</italic><sub>6</sub> protein that acts transferring electrons from cytochrome <italic>b</italic><sub>6</sub><italic>f</italic> complex to photosystem I, in photosynthesis, or cytochrome <italic>c</italic> oxidase, in respiration. In most of the cyanobacteria, at least one homologue to cytochrome <italic>c</italic><sub>6</sub> is found, the so-called cytochrome <italic>c</italic><sub>6B</sub> or cytochrome <italic>c</italic><sub>6C</sub>. However, the function of these cytochrome <italic>c</italic><sub>6</sub>-like proteins is still unknown. Recently, it has been proposed a common origin of these proteins as well as the reclassification of the cytochrome <italic>c</italic><sub>6C</sub> group as <italic>c</italic><sub>6B</sub>, renaming the new joint group as cytochrome <italic>c</italic><sub>6BC</sub>. Another homologue to cytochrome <italic>c</italic><sub>6</sub> has not been classified yet, the formerly called cytochrome <italic>c</italic><sub>6-3</sub>, which is present in the heterocyst-forming filamentous cyanobacteria <italic>Nostoc</italic> sp. PCC 7119. In this work, we propose the inclusion of this group as an independent group in the genealogy of cytochrome <italic>c</italic><sub>6</sub>-like proteins with significant differences from cytochrome <italic>c</italic><sub>6</sub> and cytochrome <italic>c</italic><sub>6BC</sub>, with the proposed name cytochrome <italic>c</italic><sub>6D</sub>. To support this proposal, new data about phylogeny, genome localisation and functional properties of cytochrome <italic>c</italic><sub>6</sub>-like proteins is provided. Also, we have analysed the interaction of cytochrome <italic>c</italic><sub>6</sub>-like proteins with cytochrome <italic>f</italic> by isothermal titration calorimetry and by molecular docking, concluding that <italic>c</italic><sub>6</sub>-like proteins could interact with cytochrome <italic>b</italic><sub>6</sub><italic>f</italic> complex in a similar fashion as cytochrome <italic>c</italic><sub>6</sub>. Finally, we have analysed the reactivity of cytochrome <italic>c</italic><sub>6</sub>-like proteins with membranes enriched in terminal oxidases of cyanobacteria by oxygen uptake experiments, concluding that cytochrome <italic>c</italic><sub>6D</sub> is able to react with the specific copper-oxidase of the heterocysts, the cytochrome <italic>c</italic> oxidase 2.</p>