Abstract
State transition is a photoacclimation mechanism for photosynthetic machinery. We previously isolated a protein supercomplex composed of photosystem (PS) I, its light-harvesting complex I (LHCI), and PSII light-harvesting complex II (LHCII) from a green alga Chlamydomonas reinhardtii in State 2. In this study, we tried to isolate a larger protein complex by using a different detergent, tridecyl maltoside. The results of sucrose density gradient and Western blot analysis indicated that the purified sample contained Cyt b6f, FNR, and PGRL1 in addition to previously isolated PSI, LHCI, and LHCII. Gel filtration and disassembling experiments showed that all of these proteins are associated and forming a single protein supercomplex. The analyses of mutants (PSI-His, ΔCyt b6f, ΔPSI) also supported such a protein supercomplex in State 2 wild-type cells. All of these protein components have been known to be essential for cyclic electron flow. Therefore, the isolated protein supercomplex in this study could drive cyclic electron flow. We will report the results of biochemical and kinetic analyses of this newly isolated supercomplex in this and next presentation, respectively.
