Binding Determinates of Sodium Hydrogen Exchanger 1 for Calcineurin Homologous Protein Isoforms 1 and 2

Abstract

The Sodium Hydrogen Exchanger, (NHE1) is an ubiquitously expressed protein that exchanges an intracellular proton (H+) for an extracellular sodium (Na+) and regulates cell volume, intracellular pH homeostasis and cell motility. The Calceurin Homologous Protein isoforms 1 (CHP1) and isoform 2 (CHP2) each regulate NHE1. CHP1 and CHP2 share a 66% amino residue homology, yet CHP1 and CHP2 have different binding affinities for NHE1. No work has determined the differential binding site for each CHP isoform. Here we will show the binding determinates of NHE and the CHP Isoforms by mutagenesis of key amino residues in the CHP binding domain from AA 803‐845. Sequence and structural analysis demonstrated that eight amino residues may play an important role in the binding of NHE1 and the CHP isoforms. These key amino residues are Asn519Ala, Asn519Asp, Ile518Gln/Ile522Gln, Il534Lys, Il537Lys, His523Gly, His523Ile, and Asp536Gly. We have expressed and purified the c‐terminus of wild‐type NHE1 and mutations for each putative CHP interaction site. The protein interactions of recombinant CHP1 and CHP2 is determined using thermal denaturation and other biophysical methods. This work will identify potential interaction sites in common and unique for each CHP isoform and NHE1.