Pharmacophore Based Screening & Modification of Amiloride Analogs for Targeting the NhaP-type Cation-Proton Antiporter in Vibrio cholerae

Abstract

The genome of Vibrio cholerae contains three structural genes for the NhaP-type cation-proton antiporter paralogues, Vc-NhaP1, 2 and 3 mediating exchange of K+ and or Na+ for protons across the membrane. Based on phenotype analysis of chromosomal Vc-NhaP1, 2 and 3 triple deletion mutants we suggested that Vc-NhaP paralogues might play a role in the Acid Tolerance Response (ATR) of V. cholerae as it passes through the gastric acid barrier of the stomach. Comparison of the biochemical properties of Vc-NhaP isoforms revealed that Vc-NhaP2 is the most active among all three paralogues. Therefore, Vc-NhaP2 antiporter is a plausible therapeutic target for developing novel inhibitors targeting these ion exchangers. Our structural and mutational analysis of Vc-NhaP2 identified a putative cation binding pocket formed by antiparallel extended regions of two transmembrane segments (TMSs V/XII) along with TMS VI. Molecular Dynamics (MD) simulations suggested that the flexibility of TMS-V/XII is crucial for the intra-molecular conformational events in Vc-NhaP2. In this study, we developed some putative Vc-NhaP2 inhibitors from Amiloride analogs (AAs). Amiloride is a potent inhibitor of human Na+/H+ exchanger-1 (NHE1). Based on the pharmacokinetic properties and potential binding affinity scores we chose six AAs showing high binding affinity scores to Vc-NhaP2. In silico, the six AAs interacted with the functionally important amino acid residues located in TMSs III, IV, V, VI, VIIII and IX either from the cytoplasmic side (three AAs) or the periplasmic side (three AAs) of Vc-NhaP2. Four AAs were modified to reduce their toxicity profile compared to the original AAs. Molecular docking of the modified AAs revealed promising binding. The four selected drugs interacted with functionally important amino acid residues located on the cytoplasmic side of TMS VI, the extended chain region of TMS V and TMS XII and the loop region between TMSs VIIII and IX. Molecular dynamics simulations revealed that binding of the selected drugs destabilized the Vc-NhaP2 and altered the flexibility of functionally important TMS VI.