title: Dos, a heme-binding PAS protein from Escherichia coli, is a direct oxygen sensor.
abstract: A direct sensor of O(2), the Dos protein, has been found in Escherichia coli. Previously, the only biological sensors known to respond to O(2) by direct and reversible binding were the FixL proteins of Rhizobia. A heme-binding region in Dos is 60% homologous to the O(2)-sensing PAS domain of the FixL protein, but the remainder of Dos does not resemble FixL. Specifically, the C-terminal domain of Dos, presumed to be a regulatory partner that couples to its heme-binding domain, is not a histidine kinase but more closely resembles a phosphodiesterase. The absorption spectra of Dos indicate that both axial positions of the heme iron are coordinated to side chains of the protein. Nevertheless, O(2) and CO bind to Dos with K(d) values of 13 and 10 microM, respectively, indicating a strong discrimination against CO binding. Association rate constants for binding of O(2) (3 mM(-)(1) s(-)(1)), CO (1 mM(-)(1) s(-)(1)) and even NO (2 mM(-)(1) s(-)(1)) are extraordinarily low and very similar. Displacement of an endogenous ligand, probably Met 95, from the heme iron in Dos triggers a conformational change that alters the activity of the enzymatic domain. This sensing mechanism differs from that of FixL but resembles that of the CO sensor CooA of Rhodospirillum rubrum. Overall the results provide evidence for a heme-binding subgroup of PAS-domain proteins whose working range, signaling mechanisms, and regulatory partners can vary considerably.
authors.affiliation: Departments of Biochemistry, Plant Biology, and Plant Biotechnology Center, The Ohio State University, Columbus, Ohio 43210-1002, USA.
authors.forename: V M
authors.initials: VM
authors.lastname: Delgado-Nixon
authors.forename: G
authors.initials: G
authors.lastname: Gonzalez
authors.forename: M A
authors.initials: MA
authors.lastname: Gilles-Gonzalez
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002248:Carbon Monoxide / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D006418:Heme / Q000378:metabolism; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000071677:Histidine Kinase; D008969:Molecular Sequence Data; D005810:Multigene Family; D009569:Nitric Oxide / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D011108:Polymers / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D013053:Spectrophotometry; D000069296:Type III Secretion Systems
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; C114344:PAS protein, E coli; D011108:Polymers; D000069296:Type III Secretion Systems; C406529:dosH protein, E coli; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; C067929:FixL protein, Bacteria; D000071677:Histidine Kinase; D010100:Oxygen