Effects of photosynthetic reaction center H protein domain mutations on photosynthetic properties and reaction center assembly in Rhodobacter sphaeroides.
Purple bacterial photosynthetic reaction center (RC) H proteins comprise three cellular domains: an 11 amino acid N-terminal sequence on the periplasmic side of the inner membrane; a single transmembrane alpha-helix; and a large C-terminal, globular cytoplasmic domain. We studied the roles of these domains in Rhodobacter sphaeroides RC function and assembly, using a mutagenesis approach that included domain swapping with Blastochloris viridis RC H segments and a periplasmic domain deletion. All mutations that affected photosynthesis reduced the amount of the RC complex. The RC H periplasmic domain is shown to be involved in the accumulation of the RC H protein in the cell membrane, while the transmembrane domain has an additional role in RC complex assembly, perhaps through interactions with RC M. The RC H cytoplasmic domain also functions in RC complex assembly. There is a correlation between the amounts of membrane-associated RC H and RC L, whereas RC M is found in the cell membrane independently of RC H and RC L. Furthermore, substantial amounts of RC M and RC L are found in the soluble fraction of cells only when RC H is present in the membrane. We suggest that RC M provides a nucleus for RC complex assembly, and that a RC H/M/L assemblage results in a cytoplasmic pool of soluble RC M and RC L proteins to provide precursors for maximal production of the RC complex.
Tehrani
Ali
A
Department of Microbiology and Immunology, University of British Columbia, 300-6174 University Boulevard, Vancouver, BC, Canada, V6T 1Z3.
Prince
Roger C
RC
Beatty
J Thomas
JT
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D002462:Cell Membrane / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010782:Photolysis; D010788:Photosynthesis / Q000235:genetics*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D010957:Plasmids; D017434:Protein Structure, Tertiary / Q000235:genetics; D012242:Rhodobacter sphaeroides / Q000737:chemistry / Q000235:genetics* / Q000254:growth & development; D012241:Rhodopseudomonas / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012995:Solubility; D013053:Spectrophotometry; D013347:Subcellular Fractions / Q000737:chemistry
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; C040330:histone-like protein HU, bacteria