Novel approach reveals localisation and assembly pathway of the PsbS and PsbW proteins into the photosystem II dimer

A blue-native gel electrophoresis system was combined with an in organello import assay to specifically analyse the location and assembly of two nuclear-encoded photosystem 11 (PSII) subunits. With this method we were able to show that initially the low molecular mass PsbW protein is not associated with the monomeric form of PSII. Instead a proportion of newly imported PsbW is directly assembled in dimeric PSH super-complexes with very fast kinetics; its negatively charged N-terminal domain is essential for this process. The chlorophyll-binding PsbS protein, which is involved in energy dissipation, is first detected in the monomeric PSII subcomplexes, and only at later time points in the dimeric form of PSII. It seems to be bound tighter to the PSII core complex than to light harvesting complex II. These data point to radically different assembly pathways for different PSII subunits. (C) 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.