title: COOH-terminal processing of polypeptide D1 of the photosystem II reaction center of Scenedesmus obliquus is necessary for the assembly of the oxygen-evolving complex.
abstract: Mutant LF-1 of the green alga Scenedesmus obliquus has been described by Metz and co-workers (Metz, J. G., Pakrasi, H., Seibert, M., and Arntzen, C. J. (1986) FEBS Lett. 205, 269-274) to be inactive for light-driven oxygen evolution, despite a functional Photo-system II reaction center. A polypeptide, D1, implicated in the ligation of the primary photoreactants of photosystem II, was shown to migrate with an apparent higher molecular mass on LDS-PAGE in the mutant than in the wild-type (WT) strain. We show here that polypeptide D1 is synthesized in a precursor form in Scenedesmus WT. Following synthesis and insertion into the thylakoid membrane, a 1.5-2-kDa oligopeptide is clipped off with a half-time of 1-2 min, yielding the mature 34-kDa form of the polypeptide. No processing of polypeptide D1 from mutant LF-1 was observed to take place. We show here that polypeptide D1 of LF-1 displays an identical proteolytic fingerprint pattern to the precursor D1 polypeptide of the wild-type strain. These both have molecular masses about 1.5-2 kDa higher than that of the mature WT polypeptide. A polyclonal antibody elicited by a synthetic oligopeptide (14-mer), predicted from the psbA gene nucleotide sequence to be homologous to the COOH terminus of the precursor D1 of spinach, cross-reacts only with D1 of mutant LF-1 and not with mature D1 of spinach, Chlamydomonas, or of Scenedesmus WT. This observation demonstrates that the greater molecular mass of polypeptide D1 from mutant LF-1 and of Scenedesmus WT precursor D1 is derived from a COOH-terminal extension. We conclude that the LF-1 mutant lacks the appropriate nuclear-encoded protease which processes polypeptide D1 at its COOH terminus from the precursor to the mature form. Such processing would appear to be a necessary step toward the stable incorporation of manganese into the oxygen-evolving site.
authors.affiliation: Central Research Department, E. I. Du Pont de Nemours Co. Incorporated, Wilmington, Delaware 19898.
authors.forename: B A
authors.initials: BA
authors.lastname: Diner
authors.forename: D F
authors.initials: DF
authors.lastname: Ries
authors.forename: B N
authors.initials: BN
authors.lastname: Cohen
authors.forename: J G
authors.initials: JG
authors.lastname: Metz
mesh_terms: D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism; D002734:Chlorophyll / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D000460:Chlorophyta / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010100:Oxygen / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational
chemical_list: D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D010100:Oxygen