Abstract
Photosystem I complex consists of 14 subunits and tightly binds LHCI to form PSI-LHCI supercomplex. It is believed that multiple steps are included in assembling a mature PSI-LHCI supercomplex from a number of subunit and cofactor components and would be assisted by several assembly factors. However, biochemical evidence is not sufficient to propose a reliable assembly mechanism. In a previous report, we identified an assembly intermediate in the green algae Chlamydomonas reinhardtii by pulse-chase protein labeling experiments. In this study, we characterized in more detail the assembly intermediate using immunochemical approach. We found that the assembly intermediate shows photosystem I activity but specifically lacks two peripheral subunits located in close proximity to LHCI. The size of the assembly intermediate was much smaller because LHCIs were easily dissociated from PSI-LHCI supercomplex during a mild detergent solubilization. Therefore, we suppose a working hypothesis of the assembly mechanism in PSI-LHCI supercomplex.
