Role of calcineurin B homologous protein in pH regulation by the Na(super +)/H(super +) exchanger 1: tightly bound Ca(super 2+) ions as important structural elements

The role of the interaction of calcineurin homologous protein 1 (CHP1) with the Na(super +)/H(super +) exchanger 1 (NHE1) in EF-hand Ca(super 2+) binding motifs, in the intracellular pH dependent regulation of NHE1 is investigated. Results revealed that complex formation between CHP1 and the CHP1 binding domain of NHE1 cause marked increase in the Ca(super 2+) binding affinity by promoting a conformational change of the EF-hands towards the tightly Ca(super 2+)-binding affinity form, indicating presence of two Ca(super 2+) ions in CHP1 when associated with NHE1 cells.