@article{oai:nagoya.repo.nii.ac.jp:00005481,
 author = {Kamiya, Takehiro and Maeshima, Masayoshi},
 issue = {1},
 journal = {Journal of Biological Chemistry},
 month = {Jan},
 note = {In plants, the cation/H^+ exchanger translocates Ca^{2+}and other metal ions into vacuoles using the H^+ gradient formed by H^+-ATPase and H^+-pyrophosphatase. Such exchangers carrying 11 transmembrane domains have been isolated from plants, yeast and bacteria. In this study, multiple sequence alignment of several cation/H^+ exchangers revealed the presence of 36 residue highly conserved regions between the 3rd and 4th, and the 8th and 9th transmembrane domains. These two repetitive motifs are designated repeats c-1 and c-2. Using site-directed mutagenesis, we generated 31 mutations in the repeats of the Oryza sativa cation/H^+ exchanger, which translocates Ca^{2+} and Mn^{2+}. Mutant exchangers were expressed in a Saccharomyces cerevisiae strain that was sensitive to Ca^{2+} and Mn^{2+} due to the absence of vacuolar Ca^{2+}-ATPase and the Ca^{2+}/H+ exchanger. Mutant exchangers were classified into 6 classes according to their tolerance to Ca^{2+ }and Mn^{2+}. For example, the class III mutants had no tolerance to either ion and the class IV mutants had tolerance only to Ca^{2+}. The biochemical function of each residue was estimated. We investigated the membrane topology of the repeats using a method combining cysteine mutagenesis with sulfhydryl reagents. Our results suggest that the repeat c-1 re-enters the membrane from the vacuolar lumen side and forms a solution-accessible region. Furthermore, several residues in repeats c-1 and c-2 were found to be conserved in animal Na+/Ca^{2+} exchangers. Finally, we suggest that these re-entrant repeats may form a vestibule or filter for cation selection.},
 pages = {812--819},
 title = {Residues in Internal Repeats of the Rice Cation/H+ Exchanger are Involved in the Transport and Selection of Cations},
 volume = {279},
 year = {2004}
}