Light-induced trimer to monomer transition in the main light-harvesting antenna complex of plants: thermo-optic mechanism.

摘要: The main chlorophyll a/b light-harvesting complex of photosystem II, LHCIIb, has earlier been shown to be capable undergoing light-induced reversible structural changes and a fluorescence quenching in way resembling those observed granal thylakoids when exposed excess light [Barzda, V., et al. (1996) Biochemistry 35, 8981-8985]. nature mechanism this unexpected flexibility not elucidated. In work, by using density gradient centrifugation nondenaturing green gel electrophoresis, as well absorbance circular dichroic spectroscopy, we show that induces significant degree monomerization, which is contrast with the preferentially trimeric organization isolated complexes dark. Monomerization accompanied release Mg ions, most likely from outer loop complexes. These data, built-in thermal instability organization, are explained terms simple theoretical model thermo-optic mechanism, effect fast transients (local T-jumps) due dissipated photon energies vicinity cation binding sites, lead thermally assisted elementary transitions. Disruption trimers monomers confined lamellar aggregates LHCII but occurs II-enriched grana membranes, intact thylakoid whole plants. As indicated differences capability monomers, appearance could facilitate nonphotochemical singlet excited state a. formation may also important regulated proteolytic degradation Structural driven mechanisms therefore provide plants novel for regulation harvesting light.