Posttranslational events leading to the assembly of photosystem II protein complex: a study using photosynthesis mutants from Chlamydomonas reinhardtii.

Abstract

Abstract. We studied the assembly of photosystem II (PSII) in several mutants from Chlamydomonas reinhardtii which were unable to synthesize either one PSII core subunit (P6 [43 kD], D1, or D2) or one oxygen-evolving enhancer (OEE1 or OEE2) subunit. Synthesis of the PSII subunits was analyzed on electrophoretograms of cells pulse labeled with [14C]acetate. Their accumulation in thylakoid membranes was studied on immunoblots, their chlorophyll-binding ability on nondenaturating gels, their assembly by detergent fractionation, their stability by pulse-chase experiments and determination of in vitro protease sensitivity, and their localization by immunocytochemistry.In Chlamydomonas, the PSII core subunits P5 (47 kD), D1, and D2 are synthesized in a concerted manner while P6 synthesis is independent. P5 and P6 accumulate independently of each other in the stacked membranes. They bind chlorophyll soon after, or concomitantly with, their synthesis and independently of the presence of the other PSII subunits. Resistance to degradation increases step by step: beginning with assembly of P5, D1, and D2, then with binding of P6, and, finally, with binding of the OEE subunits on two independent high affinity sites (one for OEE1 and another for OEE2 to which OEE3 binds). In the absence of PSII cores, the OEE subunits accumulate independently in the thylakoid lumen and bind loosely to the membranes; OEE1 was found on stacked membranes, but OEE2 was found on either stacked or unstacked membranes depending on whether or not P6 was synthesized.p HOTOSYSTEM IX (PSII) ~ is a major protein complex of the photosynthetic apparatus in oxygen-evolving species. Light-harvesting chlorophyll-protein complexes (LHCs) transfer excitons to PSII cores where primary photochemistry occurs. PSII complexes (PSII cores with oxygen-evolving enhancer [OEE] subunits) are able to carry out the oxidation of water.The PSII core comprises five main intrinsic chloroplastencoded subunits P5, P6, D1, D2, and cytochrome b559 (59). Their molecular masses vary slightly from one species to another. Two subunits of 4%50 and 43-47 kD, called P5 and P6 in Chlamydomonas reinhardtii or by their molecular mass in higher plants (respectively encoded by psbB and psbC genes), bind most of the PSII core chlorophylls (58) and form the core antenna (9, 44). The chlorophyll-P5 and chlorophyll-P6 complexes-called, respectively, CPIII and CPIV in C. reinhardtii or CP47 and CP43 in higher plantscan be separated by electrophoresis at 4°C (13, 21). D1 and D2 of 32-35 kD (encoded, respectively, by psbA and psbD genes [18,48,64]) cooperate in the binding of the primary 1. Abbreviations used in this paper: LHC, light-harvesting complex; OEE, oxygen-evolving enhancer; PSII, photosystem II; WT, wild type. reactants (44) and show sequence homologies with the subunits L and M of the reaction center from purple bacteria (39, 53). Three extrinsic polypeptides encoded by nuclear genes (12, 60) are involved in oxygen evolution; OEE1 (29-33 kD) stabilizes the association of manganese ions ...

PHOTOSYSTEM II SUBUNIT R Is Required for Efficient Binding of LIGHT-HARVESTING COMPLEX STRESS-RELATED PROTEIN3 to Photosystem II-Light-Harvesting Supercomplexes in Chlamydomonas reinhardtii

“…To confirm the absence of PSBP from FUD39, PSII-LHCII supercomplexes from the wild type and FUD39 were subjected to trypsin digestion and analyzed by mass spectrometry. These tandem mass spectrometry data demonstrated that not only PSBP but also PSBQ was absent in the PSII-LHCII supercomplexes from FUD39 (Supplemental Table S5), in accordance with a previous characterization (de Vitry et al, 1989). Moreover, to comparatively quantify PSII from the wild type and FUD39, we took advantage of isotopic labeling using differentially labeled 14 N wild-type and 15 N FUD39 cell cultures.…”

“…For comparison, we also included the FUD39 mutant that lacks PSBP (de Vitry et al, 1989) and has been shown to possess a low oxygen-evolving activity (de Vitry et al, 1989;Rova et al, 1994). Before measurements, cell cultures were incubated in LL TAP or for 24 h under HL in HSM.…”

An essential role of a TatC homologue of a ΔpH- dependent protein transporter in thylakoid membrane formation during chloroplast development in Arabidopsis thaliana

“…In yellow regions of the mutant leaves, photosynthetic protein components in the thylakoid membrane were reduced, whereas chloroplast mRNAs accumulated (24). If photosynthetic protein complexes are not assembled correctly or damaged in the thylakoid in albino or pale green mutants, the complexes together with unassembled subunit proteins are then rapidly degraded (37,38). OE23, OE17, PSII-T, and PSI-N proteins are embedded on or bound to thylakoid membrane and function in assembling of PSI and PSII complexes.…”

The Regulation of Photosynthetic Structure and Function during Nitrogen Deprivation in Chlamydomonas reinhardtii

“…Another significant posttranslational change is the relative partitioning of light-harvesting complexes between the photosystems, which occurs within 6 h, before the levels of the antennae proteins have changed significantly. Posttranslational regulation of photosynthesis is known to be important in a range of stress responses as well as in diurnal changes (de Vitry et al, 1989;Geiger and Servaites, 1994;Turkina et al, 2006;Pfalz et al, 2012). Such changes include structural modifications of individual proteins and photosynthetic complexes as well as allosteric regulation of enzyme activities.…”