The herbicide binding 32 kDa protein of thylakoid membranes functions as the apoprotein of the secondary acceptor Q B of photosystem II (PS II) (1). Additional roles have been ascribed to this protein including control of assembly of PS II reaction center (RC II) (2) and participation in the formation of RC II (3). Thus one would expect that the Q B protein should be located close to other PSII complex polypeptides. Attempts to identify polypeptides located in close proximity to the Q B protein by use of hydrophobic or hydrophilic bifunctional crosslinking reagents, have demonstrated that the Q B protein of Chlamydomonas reinhardtii thylakoids is not cross linked. However the protein cross links if the thylakoids are pretreated with β-D-octylglucoside (4). The amino acid sequence of the Q B protein is well conserved among various prokariotes, algae and higher plants (1), and thus its organization within PSII should be similar in thylakoids of various species. If this were the case then refractility to cross-linking reagents in its native state should be a general property of the Q B protein. In the present work we demonstrate that indeed this is the case. Furthermore this property can be exploited for the isolation of the Q B protein.
Noam Adir, Joseph Hirschberg, Itzhak Ohad
Journal name not available for this finding