title: Metal binding spectrum and model structure of the Bacillus anthracis virulence determinant MntA.
abstract: The potentially lethal human pathogen Bacillus anthracis expresses a putative metal import system, MntBCA, which belongs to the large family of ABC transporters. MntBCA is essential for virulence of Bacillus anthracis: deletion of MntA, the system's substrate binding protein, yields a completely non-virulent strain. Here we determined the metal binding spectrum of MntA. In contrast to what can be inferred from growth complementation studies we find no evidence that MntA binds Fe(2+) or Fe(3+). Rather, MntA binds a variety of other metal ions, including Mn(2+), Zn(2+), Cd(2+), Co(2+), and Ni(2+) with affinities ranging from 10(-6) to 10(-8) M. Binding of Zn(2+) and Co(2+) have a pronounced thermo-stabilizing effect on MntA, with Mn(2+) having a milder effect. The thermodynamic stability of MntA, competition experiments, and metal binding and release experiments all suggest that Mn(2+) is the metal that is likely transported by MntBCA and is therefore the limiting factor for virulence of Bacillus anthracis. A homology-model of MntA shows a single, highly conserved metal binding site, with four residues that participate in metal coordination: two histidines, a glutamate, and an aspartate. The metals bind to this site in a mutually exclusive manner, yet surprisingly, mutational analysis shows that for proper coordination each metal requires a different subset of these four residues. ConSurf evolutionary analysis and structural comparison of MntA and its homologues suggest that substrate binding proteins (SBPs) of metal ions use a pair of highly conserved prolines to interact with their cognate ABC transporters. This proline pair is found exclusively in ABC import systems of metal ions.
authors.affiliation: Department of Biochemistry, The Bruce and Ruth Rappaport Faculty of Medicine Technion-Israel Institute of Technology, Haifa, Israel. lewinson@tx.technion.ac.il.
authors.forename: Elena
authors.initials: E
authors.lastname: Vigonsky
authors.forename: Inbar
authors.initials: I
authors.lastname: Fish
authors.forename: Nurit
authors.initials: N
authors.lastname: Livnat-Levanon
authors.forename: Elena
authors.initials: E
authors.lastname: Ovcharenko
authors.forename: Nir
authors.initials: N
authors.lastname: Ben-Tal
authors.forename: Oded
authors.initials: O
authors.lastname: Lewinson
mesh_terms: D001408:Bacillus anthracis / Q000378:metabolism* / Q000472:pathogenicity*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002104:Cadmium / Q000378:metabolism; D003035:Cobalt / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D008670:Metals / Q000378:metabolism*; D009532:Nickel / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D014774:Virulence; D015032:Zinc / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008670:Metals; D002104:Cadmium; D003035:Cobalt; D008345:Manganese; D009532:Nickel; D015032:Zinc