Importance of Conserved Acidic Residues in MntH, the Nramp homolog of Escherichia coli
| Autor: | Heather A. H. Haemig, Robert J. Brooker |
|---|---|
| Rok vydání: | 2004 |
| Předmět: |
Physiology
Amino Acid Motifs Biophysics Biological Transport Active Biology medicine.disease_cause Metal Protein structure Escherichia coli medicine Point Mutation Cation Transport Proteins Protein secondary structure chemistry.chemical_classification Manganese Sequence Homology Amino Acid Escherichia coli Proteins Transporter Cell Biology Protein Structure Tertiary Amino acid Amino Acid Substitution Biochemistry chemistry Cytoplasm visual_art Symporter Mutagenesis Site-Directed visual_art.visual_art_medium Protein Binding |
| Zdroj: | Journal of Membrane Biology. 201:97-107 |
| ISSN: | 1432-1424 0022-2631 |
| DOI: | 10.1007/s00232-004-0711-x |
| Popis: | A bioinformatic approach was used for the identification of residues that are conserved within the Nramp family of metal transporters. Site-directed mutagenesis was then carried out to change six conserved acidic residues (i.e., Asp-34, Glu-102, Asp-109, Glu-112, Glu-154, and Asp-238) in the E. coli Nramp homolog mntH. Of these six, five of them, Asp-34, Glu-102, Asp-109, Glu-112, and Asp-238 appear to be important for function since conservative substitutions at these sites result in a substantial loss of transport function. In addition, all of the residues within the signature sequence of the Nramp family, DPGN, were also mutated in this study. Each residue was changed to several different side chains, and of ten site-directed mutations made in this motif, only P35G showed any measurable level of (54)Mn(2+) uptake with a V(max) value of approximately 10% of wild-type and a slightly elevated K(m) value. Overall, the data are consistent with a model where helix breakers in the conserved DPGN motif in TMS-1 provide a binding pocket in which Asp-34, Asn-37, Asp-109, Glu-112 (and possibly other residues) are involved in the coordination of Mn(2+). Other residues such as Glu-102 and Asp238 may play a role in the release of Mn(2+) to the cytoplasm or may be involved in maintaining secondary structure. |
| Databáze: | OpenAIRE |
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