Cleavage after residue Ala352 in the C-terminal extension is an early step in the maturation of the D1 subunit of Photosystem II in Synechocystis PCC 6803.
We have investigated the pathway by which the 16 amino-acid C-terminal extension of the D1 subunit of photosystem two is removed in the cyanobacterium Synechocystis sp. PCC 6803 to leave Ala344 as the C-terminal residue. Previous work has suggested a two-step process involving formation of a processing intermediate of D1, termed iD1, of uncertain origin. Here we show by mass spectrometry that a synthetic peptide mimicking the C- terminus of the D1 precursor is cleaved by cellular extracts or purified CtpA processing protease after residue Ala352, making this a likely site for formation of iD1. Characteristics of D1 site-directed mutants with either the Leu353 residue replaced by Pro or with a truncation after Ala352 are in agreement with this assignment. Interestingly, analysis of various CtpA and CtpB null mutants further indicate that the CtpA protease plays a crucial role in forming iD1 but that, surprisingly, low levels of C-terminal processing occur in vivo in the absence of CtpA and CtpB, possibly catalysed by other related proteases. A possible role for two-step maturation of D1 in the assembly of PSII is discussed.
Komenda
Josef
J
Institute of Microbiology, Academy of Sciences, Opatovický mlýn, 37981 Trebon, Czech Republic. komenda@alga.cz
Kuviková
Stanislava
S
Granvogl
Bernhard
B
Eichacker
Lutz A
LA
Diner
Bruce A
BA
Nixon
Peter J
PJ
D000409:Alanine / Q000737:chemistry*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011392:Proline / Q000378:metabolism*; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*
D045332:Photosystem II Protein Complex; D021122:Protein Subunits; D011392:Proline; D000409:Alanine