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

Abstract

In the Phaeodactylum tricornutum alga, as in most diatoms, cytochrome c6 is the only electron donor to photosystem I, and thus they lack plastocyanin as an alternative electron carrier. We have investigated, by using laser-flash absorption spectroscopy, the electron transfer to Phaeodactylum photosystem I from plastocyanins from cyanobacteria, green algae and plants, as compared with its own cytochrome c6. Diatom photosystem I is able to effectively react with eukaryotic acidic plastocyanins, although with less efficiency than with Phaeodactylum cytochrome c6. This efficiency, however, increases in some green alga plastocyanin mutants mimicking the electrostatics of the interaction site on the diatom cytochrome. In addition, the structure of the transient electron transfer complex between cytochrome c6 and photosystem I from Phaeodactylum has been analyzed by computational docking and compared to that of green lineage and mixed systems. Taking together, the results explain why the Phaeodactylum system shows a lower efficiency than the green systems, both in the formation of the properly arranged [cytochrome c6-photosystem I] complex and in the electron transfer itself.

The heterologous expression of a plastocyanin in the diatom Phaeodactylum tricornutum improves cell growth under iron‐deficient conditions

“…Similar functional areas have been proved to be also present in green Cc 6 (De la Rosa et al, 2006; Guss & Freeman, 1983; Hippler & Drepper, 2006; Ubbink et al, 1998). However, whereas Cc 6 from red algae and diatoms still preserves the hydrophobic ET area, it shows a significant decrease in the negative character of the electrostatic area (Akazaki et al, 2009; Bernal‐Bayard et al, 2013; Yamada et al, 2000), parallel with equivalent changes in the electrostatics features of PSI (Antoshvili et al, 2019; Bernal‐Bayard et al, 2013, 2015) and Cf (unpublished data). Consequently, in vitro kinetic analyzes of the interaction of diatom PSI with green algae and plants Pcs, suggest that if an alternative Pc in diatoms could represent a favorable adaptation to iron limitation, its “green‐type” character may, however, limit its ET efficiency.…”

“…Consequently, in vitro kinetic analyzes of the interaction of diatom PSI with green algae and plants Pcs, suggest that if an alternative Pc in diatoms could represent a favorable adaptation to iron limitation, its “green‐type” character may, however, limit its ET efficiency. Remarkably, this efficiency increased in some green alga Pc mutants replacing negative charges for positive ones to approximate the electrostatics of diatom Cc 6 (Bernal‐Bayard et al, 2015).…”

“…P. tricornutum is sensitive to iron limitation, and both lacks Pc and produces Cc 6 (Akazaki et al, 2009; Allen et al, 2008; Bernal‐Bayard et al, 2013). For this purpose, we have carried out the construction of P. tricornutum strains expressing a mutant of the Pc from the green algae Chlamydomonas reinhardtii , that was previously shown to be more effective than the WT Pc in reducing diatom PSI in vitro (Bernal‐Bayard et al, 2015).…”

Insights into the binding behavior of native and non-native cytochromes to photosystem I from Thermosynechococcus elongatus

“…Previously, a costructure of PS I with cyt c 6 was achieved by rigid body docking for the diatom Phaeodactylum tricornutum (31); here, the docking sites with the most negative energy result from interaction of cyt c 6 with PsaF. However, the closest docking site is different and has less negative binding energy.…”

Conservation of core complex subunits shaped the structure and function of photosystem I in the secondary endosymbiont alga Nannochloropsis gaditana

“…In organisms performing oxygenic photosynthesis, Photosystem I (PSI) is responsible for the light-driven electron transport from plastocyanin/cytochrome 6 to ferredoxin (Raven et al, 1999;Nelson & Yocum, 2006;Croce & van Amerongen, 2013;Bernal-Bayard et al, 2015). In eukaryotes, PSI is organized as a supercomplex composed of two moieties, the core and the peripheral antenna system.…”