1y4e
NMR structure of transmembrane segment IV of the NHE1 isoform of the Na+/H+ exchanger
Structural highlights
FunctionSL9A1_HUMAN Involved in pH regulation to eliminate acids generated by active metabolism or to counter adverse environmental conditions. Major proton extruding system driven by the inward sodium ion chemical gradient. Plays an important role in signal transduction.[1] [2] [3] Publication Abstract from PubMedThe Na(+)/H(+) exchanger isoform 1 is a ubiquitously expressed integral membrane protein that regulates intracellular pH in mammals. We characterized the structural and functional aspects of the critical transmembrane (TM) segment IV. Each residue was mutated to cysteine in cysteine-less NHE1. TM IV was exquisitely sensitive to mutation with 10 of 23 mutations causing greatly reduced expression and/or activity. The Phe(161) --> Cys mutant was inhibited by treatment with the water-soluble sulfhydryl-reactive compounds [2-(trimethylammonium)ethyl]methanethiosulfonate and [2-sulfonatoethyl]methanethiosulfonate, suggesting it is a pore-lining residue. The structure of purified TM IV peptide was determined using high resolution NMR in a CD(3)OH:CDCl(3):H(2)O mixture and in Me(2)SO. In CD(3)OH: CDCl(3):H(2)O, TM IV was structured but not as a canonical alpha-helix. Residues Asp(159)-Leu(162) were a series of beta-turns; residues Leu(165)-Pro(168) showed an extended structure, and residues Ile(169)-Phe(176) were helical in character. These three structured regions rotated quite freely with respect to the others. In Me(2)SO, the structure was much less defined. Our results demonstrate that TM IV is an unusually structured transmembrane segment that is exquisitely sensitive to mutagenesis and that Phe(161) is a pore-lining residue. Structural and functional characterization of transmembrane segment IV of the NHE1 isoform of the Na+/H+ exchanger.,Slepkov ER, Rainey JK, Li X, Liu Y, Cheng FJ, Lindhout DA, Sykes BD, Fliegel L J Biol Chem. 2005 May 6;280(18):17863-72. Epub 2005 Jan 26. PMID:15677483[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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