2kt2

Publication Abstract from PubMed

To avoid nonspecific and/or undesirable binding and reactivity of metal ions with cellular components, organisms have evolved metal-specific systems of trafficking proteins. Although systems differ, those handling soft metal ions such as Hg2+, Cu1+, Zn2+, etc., all utilize heavy metal associated (HMA) proteins and domains of ca. 70 amino acids with a conserved GMXCXXC motif in a betaalphabetabetaalphabeta structural fold. While the conserved cysteines define a common metal binding site in these proteins, other structural features must be utilized to create metal ion, protein partner and contextual specificities. This paper presents initial structure/function studies of the N-terminal HMA domain (NmerA) of Tn501 mercuric ion reductase (MerA) aimed at identifying structural features critical to its role in facilitating efficient transfer of Hg2+ to the MerA catalytic core for reductive detoxification. First, NMR solution structures of reduced and Hg2+-bound forms of NmerA are presented that allow definition and comparison of the structure of the metal binding loop in the two states. Structural differences between the two forms are compared with differences observed in three HMA domains with different metal ion and functional contexts. Second, analyses of the UV absorbance properties of wild type, Cys11Ala and Cys14Ala forms of NmerA are presented that provide assignment of the pKa values for the two cysteine thiols of the metal binding motif. Third, results from 13C-NMR studies of wild type and Y62F NmerA labeled with beta-13C-cysteine are presented that define a role for Tyr62 in modulating the pKa values of the cysteine thiols.

NmerA of Tn501 Mercuric Ion Reductase: Structural Modulation of the pKa Values of the Metal Binding Cysteine Thiols.,Ledwidge R, Hong B, Doetsch V, Miller SM Biochemistry. 2010 Sep 9. PMID:20828160^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.