Adaptation of cells to high salinity conditions and basic mechanisms of ion transport in biological membranes

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Intracellular ionic conditions are maintained within a certain range for every ions including H^+ and Na^+. Even for the higher salinity conditions of outside of the cells, cells e remove alkaline cations like Na^+ and Li+ from the inside of cells for keeping homeostasis. This exclusion of toxic alkaline cations from inside of cells is performed by Na^+/H^+ antiporters which exists in most of the cells from bacterial to human. To understand the adaptation mechanisms of cells to the high salinity conditions, molecular mechanism of Na^+/H^+ antiporters should be clarified. In this study, we analyzed molecular structure of Na^+/H^+ antipotrer NhaA from E.coli and H pylori mainly by mutagenic and biochemical studies. As the results, we have shown that essential transmembrane segments for ion transport involves TM4,5,10 and 11 and further shown that essential or important residues in these Tms (J.Biol Chem.(2003)). We also established a method by using FRET(fluorescence resonance energy tra … More nsfer) to detect protein conformational change during ion transport (Manuscript submitted). We isolated a series of mutants with substitution to Cys for each residues in the TM 4,5,10 and 11. Analyses of the mutants in terms of antiporter activities and accessibility of N-ethyl maleimide revealed presense of a putative channel like structure within the NhaA surrounded by the Tms (J.Biol Chem.(2004)). We have cloned new isoforms of human Na^+/H^+ antiporters named NHE8 and 9 and revealed their function and intracellular distribution within different intracellular vesicles (J.Biol.Chem.(2005)). These endomembrane type antiporter function as K^+/H^+ antiporter and regulate endosomal pH. We also revealed a new function of CHP we had found a binding partner of NHE1 previously. We have constructed a knockout cells of gene for CHP and found that NHE does not translocate to the cytoplasmic membrane for the knockout cells, suggesting that CHP is required for intracellular destination of NHE to the cytoplasmic membrane which differs from the previous observation by Pang et al. Less