Extensive genetic diversity in the Plasmodium falciparum Na+/H+ exchanger 1 transporter protein implicated in quinine resistance

Abstract

The Plasmodium falciparum Na(+)/H(+) exchanger (Pfnhe-1) locus at chromosome 13 and another locus at chromosome 9 have recently been proposed to influence quinine resistance. Here, we sequenced the ms4760 locus of the Pfnhe-1 gene from 244 P. falciparum isolates collected from five different regions of India. A total of 16 different ms4760 alleles (with one to five DNNND repeats) were observed among these isolates. Interestingly, areas with a high prevalence of chloroquine and sulfadoxine-pyrimethamine resistance showed more Pfnhe-1 DNNND repeats compared to low drug resistance areas. The extent of genetic diversity at the ms4760 locus also varied from one region to another, with expected heterozygosity values ranging from 0.47 to 0.88.

FIG. 1.

Map of India showing the sample collection sites.

FIG. 2.

Multiple amino acid sequence alignments of 19 ms4760 genotypes. The genotypes ms4760-2, ms4760-4, and ms4760-8 are from Ferdig et al. (8), while the rest of them are from this study. Block I represents a DNN repeat, block II represents DNNND repeats, block III is characterized by insertion and deletion of NHND residues, block IV shows insertion and deletion of the amino acids DKNNKND, block V represents DDNHNDNHNND repeats, and block VI represents DDNNNDNHNDD repeats. All other variations are highlighted. Gaps were created in order to maximize the alignment. The designations on left are microsatellite genotypes, and the numbers on right are positions of amino acids. The electropherograms were analyzed with the BioEdit Sequence Alignment Editor (10), and sequences were aligned with the GeneDoc Multiple Sequence Alignment Editor and Shading Utility (version 2.6.002).

FIG. 3.

Distribution of DNNND repeats among all of the Indian P. falciparum isolates used in this study (A) and regionwise (B). n, number of isolates.