Asp and Thr are critical for cation exchange mediated by NhaD, Na/H antiporter of Vibrio cholerae
نویسندگان
چکیده
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, GluAla, GluAla, GluAla, and AspAla, did not abolish antiport activity but shifted the pH optimum to more alkaline pH, and (ii) variants AspAla, AspAsn, and ThrAla caused a complete loss of both Na + /H + and Li + /H + antiport activity whereas the AspGlu 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 Asp and Thr in the functioning of Vc-NhaD. D 2002 Elsevier Science B.V. All rights reserved.
منابع مشابه
Functional analysis of conserved polar residues in Vc-NhaD, Na+/H+ antiporter of Vibrio cholerae.
Vc-NhaD is a Na(+)/H(+) antiporter from Vibrio cholerae with a sharp maximum of activity at pH approximately 8.0. NhaD homologues are present in many bacteria as well as in higher plants. However, very little is known about structure-function relations in NhaD-type antiporters. In this work 14 conserved polar residues associated with putative transmembrane segments of Vc-NhaD have been screened...
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