Structural and Ultrastructural Organization of Thylakoids in a Constructed Photosystem II Mutant of the Cyanobacterium Synechocystis 6803

Abstract

Photosystem (PS) II is a thylakoid-bound protein-pigment complex in plants, algae and cyanobacteria. The PSII complex is a conglomerate of around 20 different polypeptide subunits and several cofactors [1]. The reaction center of PSII consists of the D1 and D2 polypeptides and harbors the components required for charge separation [2,3]. Closely associated with the reaction center are the two subunits of cytochrome b559 and a 4.5 kDa polypeptide [4,5]. The intrinsic portion of PSII also contains the chlorophyll a-binding polypeptides CP47 and CP43. Two other intrinsic polypeptides that have recently been identified in PSII from plants are the 22 and 10 kDa polypeptides [1]. In plants and algae, three extrinsic polypeptides of 33, 23 and 16 kDa are regulatory involved in the oxygen evolving process [1]. PSII also contains several additional extrinsic and intrinsic low molecular weight polypeptides [6]. Associated with PSII is a light harvesting complex. In plants and green algae this complex contains chlorophyll a and b-binding polypeptides. In red algae and cyanobacteria the light harvesting complex is the phycobilisome, which is bound to the outer thylakoid membrane.