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Energy coupling in PSI supercomplexes
Photosystem I is an essential part of the photosynthetic machinery supplying the organism with NADPH. As an adaptive response to the variety of environmental conditions, the PSI core is supplemented with the peripheral light-harvesting antenna of different biochemical origin resulting in formation of PSI supercomplexes. This proposal focuses on the study of energy coupling of the peripheral light-harvesting complexes to the PSI core reaction center in two PSI supercomplexes that reflect two different light-harvesting strategies: 1) formation of an outer ring of CP43?around the PSI trimer in aquatic cyanobacteria under iron deficiency stress and 2) formation of a dynamic Chl a/b binding antenna that harvests solar energy and perhaps also regulates energy flowing to the PSI core in response to illumination conditions. We will examine these problems using well established tools for time-resolved spectroscopy, femtosecond absorption and fluorescence spectroscopy. The experimental plan includes studying of the energy transfer within CP43` antenna and from the CP43` ring to the PSI core. To address the issue of regulatory changes in energy coupling in the LHCI PSI supercomplexes we will use the PSI from Chlamydomonas reinhardtii fixed in State 1 or State 2 regulatory transition. To further narrow down the search for the site of energy regulation in the LHCI antenna we will establish in our lab the reconstitution procedure that will give us ability to manipulate pigment-binding sites in LHCI-730.