Characterization of the interaction between NA⁺/H⁺ exchanger isoform 7 (NHE7) and calmodulin (CaM)

• Main Author: Popova, Maria
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/24209

Na⁺/H⁺ exchangers (NHEs) are a family of transmembrane antiporters that catalyze the electroneutral exchange of Na⁺ and H⁺. They are primarily involved in regulation of pH and ion homeostasis and are themselves regulated by several signaling pathways, including Ca²⁺ signaling. NHE isoform 7 (NHE7) is activated by increases in intracellular Ca²⁺ , mediated by binding of calmodulin (CaM) to the second intracellular loop (1L2) of NHE7. This interaction between NHE7 1L2 and CaM is unconventional, as NHE7 1L2 is an extremely short CaM-binding site (∼10 amino acids) unlike previously characterized CaM-binding sites. We showed that the NHE7 1L2-CaM interaction is likely pH-independent by means of pulidown assays with GST fusion peptides of NHE7 1L2 and immobilized CaM beads performed under pH 7.3 and pH 5.8. We also showed that the NHE7 1L2-CaM interaction is mediated by positively charged and hydrophobic amino acids by means of pulidown assays with GST fusion peptides of mutant NHE7 1L2 (NHE7 1L2 KKPL, NHE7 1L2 KKRAAA and NHE7 1L2 FFAA) and immobilized CaM beads. The interaction between NHE7 1L2 and CaM has potential for relevance to the nervous system, which is highlighted by the numerous NHE isoforms that have been implicated in neuronal function: NHE1, NHE6 and NHE9. However, much future research needs to be done to elucidate the exact nature of the contribution to physiology and the nervous system of the NHE7-CaM interaction.