title: Transcriptional Regulation, Metal Binding Properties and Structure of Pden1597, an Unusual Zinc Transport Protein from Paracoccus denitrificans.
abstract: ATP-binding cassette (ABC) transporters of the cluster 9 family are ubiquitous among bacteria and essential for acquiring Zn(2+) and Mn(2+) from the environment or, in the case of pathogens, from the host. These rely on a substrate-binding protein (SBP) to coordinate the relevant metal with high affinity and specificity and subsequently release it to a membrane permease for translocation into the cytoplasm. Although a number of cluster 9 SBP structures have been determined, the structural attributes conferring Zn(2+) or Mn(2+) specificity remain ambiguous. Here we describe the gene expression profile, in vitro metal binding properties, and crystal structure of a new cluster 9 SBP from Paracoccus denitrificans we have called AztC. Although all of our results strongly indicate Zn(2+) over Mn(2+) specificity, the Zn(2+) ion is coordinated by a conserved Asp residue only observed to date as a metal ligand in Mn(2+)-specific SBPs. The unusual sequence properties of this protein are shared among close homologues, including members from the human pathogens Klebsiella pneumonia and Enterobacter aerogenes, and would seem to suggest a subclass of Zn(2+)-specific transporters among the cluster 9 family. In any case, the unusual coordination environment of AztC expands the already considerable range of those available to Zn(2+)-specific SBPs and highlights the presence of a His-rich loop as the most reliable indicator of Zn(2+) specificity.
authors: From the Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003.
authors: Melody
authors: M
authors: Handali
authors: From the Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003.
authors: Durga P
authors: DP
authors: Neupane
authors: From the Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003.
authors: Hridindu
authors: H
authors: Roychowdhury
authors: From the Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003 etyukl@nmsu.edu.
authors: Erik T
authors: ET
authors: Yukl
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites; D027682:Cation Transport Proteins / Q000378:metabolism*; D002942:Circular Dichroism; D020869:Gene Expression Profiling; D008345:Manganese / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D008969:Molecular Sequence Data; D010231:Paracoccus denitrificans / Q000378:metabolism*; D010802:Phylogeny; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D015032:Zinc / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D008670:Metals; D008345:Manganese; D015032:Zinc
keywords: ABC Transporter; Manganese; Metal Homeostasis; Metalloprotein; Transcription Regulation; Zinc