Multiconformation continuum electrostatics analysis of the NhaA Na+/H+ antiporter of Escherichia coli with functional implications.
Sodium proton antiporters are essential enzymes that catalyze the exchange of sodium ions for protons across biological membranes. Protonations and deprotonations of individual amino acid residues and of clusters formed by these residues play an important role in activating these enzymes and in the mechanism of transport. We have used multiconformation continuum electrostatics method to investigate the protonation states of residues in the sodium proton exchanger NhaA from Escherichia coli, the structure of which has been determined recently by x-ray crystallography. Our calculations identify four clusters of electrostatically tightly interacting residues as well as long-range interactions between residues required for activation. The importance of many of these residues has been demonstrated by the characterization of site-directed mutants. A number of residues with extreme pKa values, including several of the "pH sensor," can only undergo protonation/deprotonation reactions subsequent to conformational changes. The results of the calculations provide valuable information on the activation of the antiporter and the role of individual amino acid residues, and provide a solid framework for further experiments.
Olkhova
Elena
E
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max-von-Laue Strasse 3, D-60438 Frankfurt am Main, Germany.
Hunte
Carola
C
Screpanti
Emanuela
E
Padan
Etana
E
Michel
Hartmut
H
D000595:Amino Acid Sequence; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000378:metabolism*; D055672:Static Electricity; D014867:Water / Q000737:chemistry
D029968:Escherichia coli Proteins; C102839:NhaA protein, E coli; D017923:Sodium-Hydrogen Exchangers; D014867:Water