Abstract

Photosystem II (PSII) mutants are useful experimental tools to trap potential intermediates involved in the assembly of the oxygen-evolving PSII complex. Here, we focus on the subunit composition of the RC47 assembly complex that accumulates in a psbC null mutant of the cyanobacterium Synechocystis sp. PCC 6803 unable to make the CP43 apopolypeptide. By using native gel electrophoresis, we showed that RC47 is heterogeneous and mainly found as a monomer of 220 kDa. RC47 complexes co-purify with small Cab-like proteins (ScpC and/or ScpD) and with Psb28 and its homologue Psb28-2. Analysis of isolated His-tagged RC47 indicated the presence of D1, D2, the CP47 apopolypeptide, plus nine of the 13 low-molecular-mass (LMM) subunits found in the PSII holoenzyme, including PsbL, PsbM and PsbT, which lie at the interface between the two momomers in the dimeric holoenzyme. Not detected were the LMM subunits (PsbK, PsbZ, Psb30 and PsbJ) located in the vicinity of CP43 in the holoenzyme. The photochemical activity of isolated RC47-His complexes, including the rate of reduction of P680+, was similar to that of PSII complexes lacking the Mn4CaO5 cluster. The implications of our results for the assembly and repair of PSII in vivo are discussed.

Highlights

  • The photosystem II (PSII) complex is the light-driven water : plastoquinone oxidoreductase of oxygenic photosynthesis, located in the thylakoid membranes of cyanobacteria and chloroplasts [1]

  • RESULTS (a) Characterization of the RC47 assembly complex in a Synechocystis strain lacking CP43 To assess the oligomeric status of the RC47 assembly complex in vivo, we carried out a two-dimensional protein gel analysis of solubilized thylakoids isolated from radiolabelled cells of a psbC deletion mutant, DCP43, unable to synthesize CP43 [8,22]

  • Light-minus-dark difference spectra were determined in RC47-His and PSII-His at 77 K to analyse the oxidation of secondary, side-path electron donors that function in PSII at a low temperature

Read more

Summary

INTRODUCTION

The photosystem II (PSII) complex is the light-driven water : plastoquinone oxidoreductase of oxygenic photosynthesis, located in the thylakoid membranes of cyanobacteria and chloroplasts [1]. 3. RESULTS (a) Characterization of the RC47 assembly complex in a Synechocystis strain lacking CP43 To assess the oligomeric status of the RC47 assembly complex in vivo, we carried out a two-dimensional protein gel analysis of solubilized thylakoids isolated from radiolabelled cells of a psbC deletion mutant, DCP43, unable to synthesize CP43 [8,22]. In agreement with results obtained with the non-tagged strain under standard growth conditions, the level of expression of the RC47-His complex was approximately 10 per cent of the levels of PSII in WT as deduced by two-dimensional BN – PAGE and was mainly present as a monomer of size approximately 220 kDa (data not shown). Both the RC47-His and the nonoxygen-evolving PSII-His complexes displayed similar but much slower rates of P680þ reduction, on the microsecond time-scale, with time constants as previously reported for non-oxygen-evolving PSII [36]

Coomassie stain
PsbM PsbT
Findings
DISCUSSION
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.