Functional analysis of PSII-T protein of photosystem II complex from the thermophilic cyanobacterium, Thermosynechococcus (formerly Synechococcus) elongatus BP-1

Abstract

PSII-T is a membrane-spanning protein with molecular mass of 4.7 kDa, which is associated with the PSII reaction center complex. From the thermophilic cyanobacterium, Thermosynechococcus (formerly Synechococcus) elongatus BP-1, we cloned and determined the nucleotide sequence of psbB and psbT genes which encode CP47 and a small membrane protein (PSII-T) in PSII complex, respectively. We disrupted psbT gene in T. elongatus with the chloramphenicol-resistant cartridge. The mutant could grow photoautotrophically like wild type. Thylakoids and oxygen-evolving PSII core complexes were successfully isolated from the mutant as well as wild type. There was no significant difference in the oxygen-evolving activities of cells, thylakoids, or PSII complexes between the mutant and wild type. This is in contrast with the lower activities of the other PSII mutants in T. elongatus. MonoQ column chromatography revealed that recovery of the dimeric PSII in the psbT-disrupted mutant was much less than wild type. These suggest that PSII-T is specifically involved in dimerization of PSII complex or stabilization of the PSII dimer.