Supermolecular structure of photosystem II and location of the PsbS protein

This paper addresses the question of whether the PsbS protein of photosyste m two (PS II) is located within the LHC II-PS II supercomplex for which a t hree-dimensional structure has been obtained by cryoelectron microscopy and single particle analysis. The PsbS protein has recently been implicated as the site for non-photochemical quenching. Based both on immunoblotting ana lyses and structural considerations of an improved model of the spinach LHC II-PS II supercomplex, we conclude that the PsbS protein is not located wi thin the supercomplex. Analyses of other fractions resulting from the solub ilization of PS II-enriched membranes derived from spinach suggest that the PsbS protein is located in the LHC II-rich regions that interconnect the s upercomplex within the membrane.