A New Subunit of Cytochromeb 6 f Complex Undergoes Reversible Phosphorylation upon State Transition

Abstract

A 15.2-kDa polypeptide, encoded by the nuclear gene PETO, was identified as a novel cytochrome b 6 f subunit in Chlamydomonas reinhardtii. The PETO gene product is a bona fide subunit, subunit V, of the cytochrome b 6 f complex, because (i) it copurifies with the other cytochrome b 6 f subunits in the early stages of the purification procedure, (ii) it is deficient in cytochrome b 6 f mutants accumulating little of the complex, and (iii) it colocalizes with cytochrome f, which migrates between stacked and unstacked membrane regions upon state transition. Sequence analysis and biochemical characterization of subunit V shows that it has a one transmembrane ␣-helix topology with two large hydrophilic domains extending on the stromal and lumenal side of the thylakoid membranes, with a lumenal location of the N terminus. Subunit V is reversibly phosphorylated upon state transition, a unique feature that, together with its topological organization, points to the possible role of subunit V in signal transduction during redoxcontrolled short term and long term adaptation of the photosynthetic apparatus in eukaryotes.

Changes in Transcript Abundance in Chlamydomonas reinhardtii following Nitrogen Deprivation Predict Diversion of Metabolism

“…In contrast, the transcript levels of PETO were weakly increased (2-fold). This observation supports the hypothesis that this protein may have a regulatory role as opposed to being a functional cytochrome b 6 f subunit (Hamel et al, 2000), because the PETO protein is only loosely bound to the complex and its function is not required for the oxidoreductase activity. Expression of all nuclear genes encoding PSII components also decreased following N deprivation (Supplemental Table S7), although the two least abundant transcripts decreased only slightly.…”

Regulatory factors for the assembly of thylakoid membrane protein complexes

“…In addition to these subunits, additional proteins may transiently interact with the cyt b 6 f complex. In higher plants, cyt b 6 f has been co-isolated with FNR [86], and the functional coupling of a small phosphoprotein PetO to cyt b 6 f has been reported [87]. PetP has been proposed as a new cyanobacterial cyt b 6 f subunit that might be analogous to PetO [88].…”

Environmentally Modulated Phosphoproteome of Photosynthetic Membranes in the Green Alga Chlamydomonas reinhardtii

“…To date, protein phosphorylation in photosynthetic membranes of plants and algae has been studied by seven different techniques: (i) radioactive labeling (4,6,8,9,24,25), (ii) detection of the shift in the electrophoretic mobility of individual proteins (24, 26 -28), (iii) immunological analyses with anti-phosphoamino acid antibodies (27)(28)(29)(30), (iv) site-directed mutagenesis of potential protein phosphorylation sites (31)(32)(33), (v) mass spectrometric determination of the masses for intact phosphorylated proteins (34,35), (vi) amino-terminal protein sequencing by Edman degradation (36,37), and (vii) identification and mass spectrometric sequencing of phosphorylated peptides obtained by proteolytic treatment of the membranes (38 -41). None of these techniques is ideal, and the identification of protein phosphorylation events largely depends on the detection method used (28).…”