title: Diversification and spectral tuning in marine proteorhodopsins.
abstract: Proteorhodopsins, ubiquitous retinylidene photoactive proton pumps, were recently discovered in the cosmopolitan uncultured SAR86 bacterial group in oceanic surface waters. Two related proteorhodopsin families were found that absorb light with different absorption maxima, 525 nm (green) and 490 nm (blue), and their distribution was shown to be stratified with depth. Using structural modeling comparisons and mutagenesis, we report here on a single amino acid residue at position 105 that functions as a spectral tuning switch and accounts for most of the spectral difference between the two pigment families. Furthermore, looking at natural environments, we found novel proteorhodopsin gene clusters spanning the range of 540-505 nm and containing changes in the same identified key switch residue leading to changes in their absorption maxima. The results suggest a simultaneous diversification of green proteorhodopsin and the new key switch variant pigments. Our observations demonstrate that this single-residue switch mechanism is the major determinant of proteorhodopsin wavelength regulation in natural marine environments.
authors.affiliation: Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Dikla
authors.initials: D
authors.lastname: Man
authors.forename: Weiwu
authors.initials: W
authors.lastname: Wang
authors.forename: Gazalah
authors.initials: G
authors.lastname: Sabehi
authors.forename: L
authors.initials: L
authors.lastname: Aravind
authors.forename: Anton F
authors.initials: AF
authors.lastname: Post
authors.forename: Ramon
authors.initials: R
authors.lastname: Massana
authors.forename: Elena N
authors.initials: EN
authors.lastname: Spudich
authors.forename: John L
authors.initials: JL
authors.lastname: Spudich
authors.forename: Oded
authors.initials: O
authors.lastname: Béjà
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D004269:DNA, Bacterial; D006863:Hydrogen-Ion Concentration; D008027:Light; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009792:Oceans and Seas; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012243:Rhodopsin / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D025604:Rhodopsins, Microbial; D016415:Sequence Alignment; D013050:Spectrometry, Fluorescence
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D012243:Rhodopsin