title: High-affinity metal binding by the Escherichia coli [NiFe]-hydrogenase accessory protein HypB is selectively modulated by SlyD.
abstract: [NiFe]-hydrogenase, which catalyzes the reversible conversion between hydrogen gas and protons, is a vital component of the metabolism of many pathogens. Maturation of [NiFe]-hydrogenase requires selective nickel insertion that is completed, in part, by the metallochaperones SlyD and HypB. Escherichia coli HypB binds nickel with sub-picomolar affinity, and the formation of the HypB-SlyD complex activates nickel release from the high-affinity site (HAS) of HypB. In this study, the metal selectivity of this process was investigated. Biochemical experiments revealed that the HAS of full length HypB can bind stoichiometric zinc. Moreover, in contrast to the acceleration of metal release observed with nickel-loaded HypB, SlyD blocks the release of zinc from the HypB HAS. X-ray absorption spectroscopy (XAS) demonstrated that SlyD does not impact the primary coordination sphere of nickel or zinc bound to the HAS of HypB. Instead, computational modeling and XAS of HypB loaded with nickel or zinc indicated that zinc binds to HypB with a different coordination sphere than nickel. The data suggested that Glu9, which is not a nickel ligand, directly coordinates zinc. These results were confirmed through the characterization of E9A-HypB, which afforded weakened zinc affinity compared to wild-type HypB but similar nickel affinity. This mutant HypB fully supports the production of [NiFe]-hydrogenase in E. coli. Altogether, these results are consistent with the model that the HAS of HypB functions as a nickel site during [NiFe]-hydrogenase enzyme maturation and that the metal selectivity is controlled by activation of metal release by SlyD.
authors.affiliation: Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada. dzamble@chem.utoronto.ca.
authors.forename: Mozhgan
authors.initials: M
authors.lastname: Khorasani-Motlagh
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Lacasse
authors.forename: Deborah B
authors.initials: DB
authors.lastname: Zamble
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006864:Hydrogenase / Q000378:metabolism*; D008958:Models, Molecular; D009532:Nickel / Q000378:metabolism; D019696:Peptidylprolyl Isomerase / Q000378:metabolism*; D011485:Protein Binding; D015032:Zinc / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; C490324:HypB protein, E coli; C085606:SlyD protein, E coli; D009532:Nickel; C043296:nickel-iron hydrogenase; D006864:Hydrogenase; D019204:GTP-Binding Proteins; D019696:Peptidylprolyl Isomerase; D015032:Zinc