General occurrence and structural similarity of the rapidly synthesized, 32,000-dalton protein of the chloroplast membrane

Abstract

A rapidly metabolized membrane protein from Spirodela, with an apparent molecular weight of 32,000, has been implicated in allosterically regulating electron transport and mediating diuron herbicide sensitivity in the chloroplast (Mattoo, A. K., Pick, U., Hoffman-Falk, H., and Edelman, M. (1981) Proc. Natl. Acad. Sci. U. S. A. 78, 1572-1576). Rapid synthesis of a 32,000-dalton plastid membrane protein is demonstrated for several diverse angiosperms and the alga, Chlamydomonas. Comparative partial proteolytic mapping of the polypeptide showed similar patterns for all species tested. In some cases, a 33,500-dalton precursor polypeptide was identified which also displayed interspecific structural homologies. Lastly, in situ analysis of the surface-exposed 32,000-dalton membrane protein yielded a common trypsinization pattern for the organisms studied. These findings point toward a broad distribution and phylogenetic similarity of the 32,000-dalton thylakoid protein of the chloroplast at levels of precursor maturation, membrane orientation, and primary structure.