Functional Analysis of Conserved Transmembrane Charged Residues and a Yeast Specific Extracellular Loop of the Plasma Membrane Na+/H+ Antiporter of Schizosaccharomyces pombe

Cation Transporters of Candida albicans-New Targets to Fight Candidiasis?

Candidiasis is the wide-spread fungal infection caused by numerous strains of yeast, with the prevalence of Candida albicans. The current treatment of candidiasis is becoming rather ineffective and costly owing to the emergence of resistant strains; hence, the exploration of new possible drug targets is necessary. The most promising route is the development of novel antibiotics targeting this pathogen. In this review, we summarize such candidates found in C. albicans and those involved in the transport of (metal) cations, as the latter are essential for numerous processes within the cell; hence, disruption of their fluxes can be fatal for C. albicans.

Acidic residues of extracellular loop 3 of the Na+/H+ exchanger type 1 are important in cation transport

Mammalian Na⁺/H⁺ exchanger type I isoform (NHE1) is a ubiquitously expressed membrane protein that regulates intracellular pH (pHi) by removing one intracellular proton in exchange for one extracellular sodium ion. Abnormal activity of the protein occurs in cardiovascular disease and breast cancer. The purpose of this study is to examine the role of negatively charged amino acids of extracellular loop 3 (EL3) in the activity of the NHE protein. We mutated glutamic acid 217 and aspartic acid 226 to alanine, and to glutamine and asparagine, respectively. We examined effects on expression levels, cell surface targeting and activity of NHE1, and also characterized affinity for extracellular sodium and lithium ions. Individual mutation of these amino acids had little effect on protein function. However, mutation of both these amino acids together impaired transport, decreasing the Vmax for both Na⁺ and Li⁺ ions. We suggested that amino acids E217 and D226 form part of a negatively charged coordination sphere, which facilitates cation transport in the NHE1 protein.

Physiological, Structural, and Functional Analysis of the Paralogous Cation-Proton Antiporters of NhaP Type from Vibrio cholerae

The transmembrane K⁺/H⁺ antiporters of NhaP type of Vibrio cholerae (Vc-NhaP1, 2, and 3) are critical for maintenance of K⁺ homeostasis in the cytoplasm. The entire functional NhaP group is indispensable for the survival of V. cholerae at low pHs suggesting their possible role in the acid tolerance response (ATR) of V. cholerae. Our findings suggest that the Vc-NhaP123 group, and especially its major component, Vc-NhaP2, might be a promising target for the development of novel antimicrobials by narrowly targeting V. cholerae and other NhaP-expressing pathogens. On the basis of Vc-NhaP2 in silico structure modeling, Molecular Dynamics Simulations, and extensive mutagenesis studies, we suggest that the ion-motive module of Vc-NhaP2 is comprised of two functional regions: (i) a putative cation-binding pocket that is formed by antiparallel unfolded regions of two transmembrane segments (TMSs V/XII) crossing each other in the middle of the membrane, known as the NhaA fold; and (ii) a cluster of amino acids determining the ion selectivity.