Biomaterial Database

Molecular physiology of the Na+/H+ antiporter in Escherichia coli. 1994

E Padan, and S Schuldiner

Department of Molecular and Microbial Ecology, Hebrew University of Jerusalem, Israel.

All living cells maintain an inwardly directed Na+ gradient and a constant intracellular pH. Na+/H+ antiporters have been assigned an essential role in these homeostatic mechanisms in all cells. In Escherichia coli, two Na+/H+ antiporter genes, nhaA and nhaB, have been cloned. Deletion of either one or both showed that NhaA is essential for adaptation to high salinity, for growth at alkaline pH in the presence of Na+ and for challenging Li+ toxicity. NhaB confers tolerance to low levels of Na+ and becomes essential when the activity of NhaA limits growth. The adaptive response to Na+ is mediated by the positive regulator nhaR, which transduces the signal (intracellular Na+) to expression of the nhaA gene. We have identified Glu-134 of NhaR as part of the 'Na+ sensor' of NhaA. In agreement with the role of NhaA in pH homeostasis, its Na(+)-dependent expression is enhanced at alkaline pH. Reconstitution of pure NhaA and NhaB in proteoliposomes demonstrates that, whereas both are electrogenic (the H+/Na+ stoichiometry of NhaA is 2), only NhaA is pH-dependent, increasing its activity 1000-fold between pH 7 and 8.5. Mutating all the histidines of NhaA shows that His-226 is part of the 'pH sensor' of NhaA.

UI	MeSH Term	Description	Entries
D008954	Models, Biological	Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.	Biological Model,Biological Models,Model, Biological,Models, Biologic,Biologic Model,Biologic Models,Model, Biologic
D008969	Molecular Sequence Data	Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.	Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D004926	Escherichia coli	A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.	Alkalescens-Dispar Group,Bacillus coli,Bacterium coli,Bacterium coli commune,Diffusely Adherent Escherichia coli,E coli,EAggEC,Enteroaggregative Escherichia coli,Enterococcus coli,Diffusely Adherent E. coli,Enteroaggregative E. coli,Enteroinvasive E. coli,Enteroinvasive Escherichia coli
D005798	Genes, Bacterial	The functional hereditary units of BACTERIA.	Bacterial Gene,Bacterial Genes,Gene, Bacterial
D006706	Homeostasis	The processes whereby the internal environment of an organism tends to remain balanced and stable.	Autoregulation
D000595	Amino Acid Sequence	The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.	Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein
D014158	Transcription, Genetic	The biosynthesis of RNA carried out on a template of DNA. The biosynthesis of DNA from an RNA template is called REVERSE TRANSCRIPTION.	Genetic Transcription
D015964	Gene Expression Regulation, Bacterial	Any of the processes by which cytoplasmic or intercellular factors influence the differential control of gene action in bacteria.	Bacterial Gene Expression Regulation,Regulation of Gene Expression, Bacterial,Regulation, Gene Expression, Bacterial
D017433	Protein Structure, Secondary	The level of protein structure in which regular hydrogen-bond interactions within contiguous stretches of polypeptide chain give rise to ALPHA-HELICES; BETA-STRANDS (which align to form BETA-SHEETS), or other types of coils. This is the first folding level of protein conformation.	Secondary Protein Structure,Protein Structures, Secondary,Secondary Protein Structures,Structure, Secondary Protein,Structures, Secondary Protein
D017923	Sodium-Hydrogen Exchangers	A family of plasma membrane exchange glycoprotein antiporters that transport sodium ions and protons across lipid bilayers. They have critical functions in intracellular pH regulation, cell volume regulation, and cellular response to many different hormones and mitogens.	Na(+)-H(+)-Antiporter,Na(+)-H(+)-Exchanger,Sodium-Hydrogen Antiporter,Na(+)-H(+)-Antiporters,Na(+)-H(+)-Exchangers,SLC9 Na(+)-H(+) Exchangers,SLC9 Protein Family,SLC9 Proteins,SLC9-NHE Protein Family,Sodium-Hydrogen Antiporters,Sodium-Hydrogen Exchanger,Sodium-Proton Antiporter,Sodium-Proton Antiporters,Solute Carrier 9 Protein Family,Solute Carrier 9 Proteins,Antiporter, Sodium-Hydrogen,Antiporter, Sodium-Proton,Antiporters, Sodium-Hydrogen,Antiporters, Sodium-Proton,Exchanger, Sodium-Hydrogen,Exchangers, Sodium-Hydrogen,Protein Family, SLC9,Protein Family, SLC9-NHE,SLC9 NHE Protein Family,Sodium Hydrogen Antiporter,Sodium Hydrogen Antiporters,Sodium Hydrogen Exchanger,Sodium Hydrogen Exchangers,Sodium Proton Antiporter,Sodium Proton Antiporters