A CURRENT ASSESSMENT OF PHOTOSYSTEM-II STRUCTURE

This review covers the recent progress in the elucidation of the struc ture of photosystem II (PSII). Because much of the structural informat ion for this membrane protein complex has been revealed by electron mi croscopy (EM), the review will also consider the specific technical an d interpretation problems that arise with EM where they are of particu lar relevance to the structural data. Most recent reviews of photosyst em II structure have concentrated on molecular studies of the PSII gen es and on the likely roles of the subunits that they encode or they we re mainly concerned with the biophysical data and fast absorption spec troscopy largely relating to electron transfer in various purified PSI I preparations. In this review, we will focus on the approaches to the three-dimensional architecture of the complex and the lipid bilayer i n which it is located (the thylakoid membrane) with special emphasis p laced upon electron microscopical studies of PSII-containing thylakoid membranes. There are a few reports of 3D crystals of PSII and of asso ciated X-ray diffraction measurements and although little structural i nformation has so far been obtained from such studies (because of the lack of 3D crystals of sufficient quality), the prospects for such stu dies are also assessed.