Organization of transmembrane helices in photosystem II: comparison of plants and cyanobacteria.
Electron microscopy and X-ray crystallography are revealing the structure of photosystem II. Electron crystallography has yielded a 3D structure at sufficient resolution to identify subunit positioning and transmembrane organization of the reaction-centre core complex of spinach. Single-particle analyses are providing 3D structures of photosystem II-light-harvesting complex II supercomplexes that can be used to incorporate high-resolution structural data emerging from electron and X-ray crystallography. The positions of the chlorins and metal centres within photosystem II are now available. It can be concluded that photosystem II is a dimeric complex with the transmembrane helices of CP47/D2 proteins related to those of the CP43/D1 proteins by a twofold axis within each monomer. Further, both electron microscopy and X-ray analyses show that P(680) is not a 'special pair' and that cytochrome b559 is located on the D2 side of the reaction centres some distance from P(680). However, although comparison of the electron microscopy and X-ray models for spinach and Synechococcus elongatus show considerable similarities, there seem to be differences in the number and positioning of some small subunits.
Barber
J
J
Department of Biological Sciences, Wolfson Laboratories, Imperial College of Science, Technology and Medicine, London SW7 2AZ, UK. j.barber@ic.ac.uk
Nield
J
J
D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry*; D019281:Dimerization; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000648:ultrastructure; D045332:Photosystem II Protein Complex; D010944:Plants / Q000737:chemistry*; D011487:Protein Conformation
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex