title: The PufX protein of Rhodobacter capsulatus affects the properties of bacteriochlorophyll a and carotenoid pigments of light-harvesting complex 1.
abstract: A pufX gene deletion in the purple bacterium Rhodobacter capsulatus causes a severe photosynthetic defect and increases core light-harvesting complex (LH1) protein and bacteriochlorophyll a (BChl) levels. It was suggested that PufX interrupts the LH1 alpha/beta ring around the reaction centre, allowing quinone/quinol exchange. However, naturally PufX(-) purple bacteria grow photosynthetically with an uninterrupted LH1. We discovered that substitutions of the Rhodobacter-specific LH1 alpha seryl-2 decrease carotenoid levels in PufX(-)R. capsulatus. An LH1 alphaS2F mutation improved the photosynthetic growth of a PufX(-) strain lacking the peripheral LH2 antenna, although LH1 BChl absorption remained above wild-type, suggesting that Rhodobacter-specific carotenoid binding is involved in the PufX(-) photosynthetic defect and LH1 expansion is not. Furthermore, PufX overexpression increased LH1-like BChl absorption without inhibiting photosynthetic growth. PufX(+) LH1 alphaS2-substituted mutant strains had wild-type carotenoid levels, indicating that PufX modulates LH1 carotenoid binding, inducing a conformational change that favours quinone/quinol exchange.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, 300-6174 University Blvd. Vancouver, BC, Canada V6T 1Z3. muktak@microbio.umass.edu
authors.forename: Muktak
authors.initials: M
authors.lastname: Aklujkar
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Beatty
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D025541:Bacteriochlorophyll A / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010860:Pigments, Biological / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D025541:Bacteriochlorophyll A; D045342:Light-Harvesting Protein Complexes; D010860:Pigments, Biological; C088749:PufX protein, Rhodobacter; D011994:Recombinant Proteins; C094744:light-harvesting complex 1, Rhodospirillum; D002338:Carotenoids