The photosynthetic Cytochrome c550 from the diatom Phaeodactylum tricornutum

Resumen del trabajo presentado a la 7th International Conference Photosynthesis Research and Sustainability, celebrada en Pushchino (Rusia) del 19 al 25 de junio de 2016.Cytochrome c550 (Cc550) is a c-type beme protein with a bis-histidinyl axial coordination adscribed as an extrinsic component in the luminal side of photo-system ll (PS II), although its role within this complex is not yet well established. Cc550 is present in cyanobacteria as well as in eukaryotic algae from the red photosynthetic lineage, which includes diatoms. However, the protein is absent in the green lineage, which comprises green algae and plants. We have here characterized the Cc550 from the diatom Phaeodactylum tricornutum. Cc550 is mostly obtained from the soluble cell extract in relatively large amounts. In addition, the protein appeared to be truncated in the last hydropbobic residues of the C-terminal, as deduced by MS analysis and the comparison with the gene sequence. Interestingly, in cyanobacteria it has been described that the C-terminus of Cc550 forms a hydrophobic finger involved in the interaction with PS II Cc550 was absent in solubilized PS ll complex samples, that are not able to (in)ncorporate the cytochrome after further incubation with an excess of the purified protein, thus indicating a low affinity of Cc550 for the PS II complex. Under iron-limiting conditions the amount of Cc550 decreases up to about 50% as compared to iron-replete cells, pointing to an iron-regulated production. Oxidized Cc550 has been further characterized using continuous wave (CW) EPR and pulse techniques, including ESEEM and HYSCORE, the results indicate a distortion of the heme-axial ligands and loss of the co-planarity of the imidazole ring, as well as relevant changes in the structure of the single occupied molecular orbital (SOMO) of the heme centre.Peer Reviewe