title: A hemerythrin-like domain in a bacterial chemotaxis protein.
abstract: Hemerythrin (Hr) is an O(2)-carrying protein found in some marine invertebrates. A conserved sequence motif in all Hrs provides five histidine and two carboxylate ligands to an oxo-/hydroxo-bridged diiron active site, as well as a hydrophobic O(2) binding pocket. Database searches located a previously unrecognized Hr-like sequence motif at the 3' end of the gene, dcrH, from the anaerobic sulfate-reducing bacterium, Desulfovibrio (D.) vulgaris (Hildenborough). This gene encodes a putative methyl-accepting chemotaxis protein, DcrH. We have established by immunoblotting that a full-length DcrH, including the Hr-like domain, is expressed in D. vulgaris (Hildenborough). The C-terminal domain of DcrH, when expressed separately in recombinant form in Escherichia coli, was found to fold into a stable protein, DcrH-Hr. The UV-vis absorption and resonance Raman spectra of DcrH-Hr, and of its azide adduct, provide clear evidence for an oxo-bridged diiron(III) site very similar to that found in Hr. Based on UV-vis absorption spectra, exposure of the reduced (colorless, presumably diferrous) DcrH-Hr to air resulted in formation of an O(2) adduct also very similar to that of Hr. Unlike that of Hr, the O(2) adduct of DcrH-Hr autoxidized within a few minutes at room temperature. The O(2) binding pocket of DcrH-Hr appears to be larger than that of Hr. Given the air-sensitive nature of D. vulgaris and the putative chemotactic function of DcrH, one possible role for the Hr-like domain of DcrH is O(2)-sensing. DcrH-Hr is the first characterized example of a Hr-like protein from any microorganism.
authors.affiliation: Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia, Athens, Georgia 30602-2556, USA.
authors.forename: J
authors.initials: J
authors.lastname: Xiong
authors.forename: D M
authors.initials: DM
authors.lastname: Kurtz
authors.forename: J
authors.initials: J
authors.lastname: Ai
authors.forename: J
authors.initials: J
authors.lastname: Sanders-Loehr
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002633:Chemotaxis; D003001:Cloning, Molecular; D016969:Desulfovibrio vulgaris / Q000737:chemistry* / Q000235:genetics; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics; D006422:Hemerythrin / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D006422:Hemerythrin