Document Detail

Conserved low-affinity nickel-binding amino acids are essential for the function of the nickel permease NixA of Helicobacter pylori.
MedLine Citation:
PMID:  11844775     Owner:  NLM     Status:  MEDLINE    
Nickel acquisition is necessary for urease activity, a major virulence factor of the human gastric pathogen Helicobacter pylori. The nickel permease NixA of H. pylori is a member of the single-component nickel-cobalt transporter family. To identify functionally relevant amino acids of NixA, single-site exchanges were introduced into NixA via PCR-based mutagenesis. This study investigated one of the recognition motifs for this family in transmembrane segment III and other conserved amino acids, mostly with possible nickel-binding capacities. The mutant alleles were expressed in Escherichia coli, and activity of the altered permeases was analyzed by measuring nickel accumulation and urease activity. Expression was checked by immunoblotting after sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a NixA-specific antibody. Replacement of Phe-75 and His-79-both part of the characteristic sequence motif-and of Asn-127, Thr-195, and Ser-197 with alanine abolished nickel uptake in the E. coli system. The results were unchanged if these amino acids were replaced with residues more similar to the original amino acid. The phenotype of the null mutants was independent of the culture medium. Mutation of Val-82, Tyr-242, Thr-260, His-181, and His-15 strongly affected uptake activity under nickel limitation on complex Luria-Bertani medium but had little effect in minimal medium. Eight other conserved amino acids (Ser-80, Ser-81, Phe-119, Trp-180, Tyr-183, Trp-244, Pro-249, and Asn-256) were found to be dispensable for the function of NixA. These results show that atypical nickel-binding amino acids play an important function in nickel uptake and that most of the essential amino acids are clustered in conserved motifs.
Lutz Wolfram; Peter Bauerfeind
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of bacteriology     Volume:  184     ISSN:  0021-9193     ISO Abbreviation:  J. Bacteriol.     Publication Date:  2002 Mar 
Date Detail:
Created Date:  2002-02-14     Completed Date:  2002-03-28     Revised Date:  2013-04-18    
Medline Journal Info:
Nlm Unique ID:  2985120R     Medline TA:  J Bacteriol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1438-43     Citation Subset:  IM    
Department of Internal Medicine, Division of Gastroenterology, University Hospital Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland.
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MeSH Terms
Amino Acid Motifs
Bacterial Proteins / chemistry*,  genetics,  metabolism*
Cation Transport Proteins / chemistry*,  genetics,  metabolism*
Cell Membrane / metabolism
Conserved Sequence
Helicobacter pylori / enzymology*
Molecular Sequence Data
Mutagenesis, Site-Directed
Nickel / metabolism*
Urease / metabolism
Reg. No./Substance:
0/Bacterial Proteins; 0/Cation Transport Proteins; 0/NixA protein, Helicobacter pylori; 7440-02-0/Nickel; EC

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