Crystallization and Structural Analysis of Cytochromec₆from the DiatomPhaeodactylum tricornutumat 1.5 Å Resolution

Interaction of photosystem I from Phaeodactylum tricornutum with plastocyanins as compared with its native cytochrome c6: Reunion with a lost donor

“…In Phaeodactylum, Cyt acts as the only electron donor to PSI since this organism, as most diatoms, lacks Pc [3,8]. Here, by using laser-flash absorption spectroscopy, we have analyzed cross-reactions between Pc donor proteins from cyanobacteria, green alga and plant species with Phaeodactylum PSI.…”

“…Considering the different electrostatic features of Phaeodactylum Cyt and the different Pcs [8,17,20], an analysis of the effect of ionic strength on the process was also performed ( Fig. 1, right; and Fig.…”

“…This behavior could be explained by the different intrinsic efficiency of cofactors -exposed heme vs. a hindered Cu cofactor -or different surface steric properties. From the solved crystal structure of Phaeodactylum Cyt, turns out that this protein has evolved towards a decrease in the acidic area thought to be involved in the interaction with PSI (revised in [47], and see [8,17]) (Fig. 3).…”

“…To understand the structural and energetic determinants of the differences in efficiency observed in diatom PSI reduction with respect to the green systems [17], computational docking simulations were performed between the modeled structure of PSI from Phaeodactylum (see Experimental procedures section) and both its native Cyt (PDB entry 3DMI) [8] and the corresponding Cyt from the green alga Monoraphidium (PDB entry 1CTJ) [48], for which kinetic data for the ET to diatom PSI have been previously reported [17]. We note that while we were preparing this manuscript, a new structure for PSI from the plant P. sativum (PDB 4Y28) has been reported [49], with a slightly better sequence identity with Phaeodactylum PsaF (53%).…”

“…Consequently, the photosynthetic machinery in diatoms possesses some singularities, arising from their evolutionary history and endosymbiotic origin [5][6][7]. In particular, while most cyanobacteria and unicellular green algae contain both the copper-protein plastocyanin (Pc) and the iron-containing cytochrome c 6 (Cyt) as alternative soluble electron carriers between the b 6 f and photosystem I (PSI) membrane complexes, most diatoms lack Pc, thus containing Cyt as the only soluble carrier between these complexes [8], with the remarkable exception of the oceanic centric diatom Thalassiosira oceanica, for which the presence of an unusual Pc has been reported [9].…”