Asp and Thr are critical for cation exchange mediated by NhaD, Na/H antiporter of Vibrio cholerae |
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Authors: | Elena OstroumovJudith Dzioba Peter C LoewenPavel Dibrov |
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Institution: | Faculty of Science, Department of Microbiology, University of Manitoba, R3T 2N2 Winnipeg, Manitoba, Canada |
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Abstract: | The Vc-NhaD is an Na+/H+ antiporter from Vibrio cholerae belonging to a new family of bacterial Na+/H+ antiporters, the NhaD family. In the present work we mutagenized five conserved Asp and Glu residues and one conserved Thr residue to Ala in order to identify amino acids that are critical for the antiport activity. All mutations fall into two distinct groups: (i) four variants, Glu100Ala, Glu251Ala, Glu342Ala, and Asp393Ala, did not abolish antiport activity but shifted the pH optimum to more alkaline pH, and (ii) variants Asp344Ala, Asp344Asn, and Thr345Ala caused a complete loss of both Na+/H+ and Li+/H+ antiport activity whereas the Asp344Glu variant exhibited reduced Na+/H+ and Li+/H+ antiport activity. This is the first mutational analysis of the antiporter of NhaD type and the first demonstration of Thr residue being indispensable for Na+/H+ antiport. We discuss the possible role of Asp344 and Thr345 in the functioning of Vc-NhaD. |
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Keywords: | Na+/H+ antiport Vibrio cholerae Site-directed mutagenesis Cation-binding site |
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