title: Evolutionary migration of a post-translationally modified active-site residue in the proton-pumping heme-copper oxygen reductases.
abstract: In the respiratory chains of aerobic organisms, oxygen reductase members of the heme-copper superfamily couple the reduction of O2 to proton pumping, generating an electrochemical gradient. There are three distinct families of heme-copper oxygen reductases: A, B, and C types. The A- and B-type oxygen reductases have an active-site tyrosine that forms a unique cross-linked histidine-tyrosine cofactor. In the C-type oxygen reductases (also called cbb3 oxidases), an analogous active-site tyrosine has recently been predicted by molecular modeling to be located within a different transmembrane helix in comparison to the A- and B-type oxygen reductases. In this work, Fourier-transform mass spectrometry is used to show that the predicted tyrosine forms a histidine-tyrosine cross-linked cofactor in the active site of the C-type oxygen reductases. This is the first known example of the evolutionary migration of a post-translationally modified active-site residue. It also verifies the presence of a unique cofactor in all three families of proton-pumping respiratory oxidases, demonstrating that these enzymes likely share a common reaction mechanism and that the histidine-tyrosine cofactor may be a required component for proton pumping.
authors.affiliation: Department of Chemistry, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: James
authors.initials: J
authors.lastname: Hemp
authors.forename: Dana E
authors.initials: DE
authors.lastname: Robinson
authors.forename: Krithika B
authors.initials: KB
authors.lastname: Ganesan
authors.forename: Todd J
authors.initials: TJ
authors.lastname: Martinez
authors.forename: Neil L
authors.initials: NL
authors.lastname: Kelleher
authors.forename: Robert B
authors.initials: RB
authors.lastname: Gennis
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D003300:Copper / Q000737:chemistry*; D003579:Cytochrome Reductases / Q000737:chemistry / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D006418:Heme / Q000737:chemistry*; D008969:Molecular Sequence Data; D011499:Protein Processing, Post-Translational / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D017494:Proton Pumps / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000201:enzymology; D014734:Vibrio cholerae / Q000201:enzymology / Q000235:genetics
chemical_list: D017494:Proton Pumps; D006418:Heme; D003300:Copper; D003579:Cytochrome Reductases; C414443:cbb3 oxidase; D003576:Electron Transport Complex IV