PSD‐95 interacts with NBCn1 and enhances channel‐like activity without affecting cotransport function

Abstract

NBCn1 plays an essential role in intracellular pH regulation and transepithelial bicarbonate movement in the body. NBCn1 also has sodium channel‐like activity uncoupled to Na/HCO3 cotransport. We previously reported that NBCn1 interacts with the postsynaptic density protein PSD‐95 in the brain. Here, we elucidated the structural determinant and functional consequence of NBCn1/PSD‐95 interaction. In rat hippocampal CA3 neurons, NBCn1 was localized to the postsynaptic membranes of both dendritic shafts and spines and occasionally to the presynaptic membranes. A GST/NBCn1 fusion protein containing the C‐terminal 131 amino acids of NBCn1 pulled down PSD‐95 from rat brain lysates, whereas GST/NBCn1‐ΔETSL (deletion of the last four amino acids) and GST/NBCn2 lacking the same ETSL did not. NBCn1 and PSD‐95 were coimmunoprecipitated in HEK 293 cells. PSD‐95 has negligible effects on intracellular pH changes mediated by NBCn1 in HEK 293 cells and Xenopus oocytes. However, PSD‐95 increased an ionic conductance produced by NBCn1 channel‐like activity. This increase was abolished by NBCn1‐ΔETSL or by the peptide containing the last 15 amino acids of NBCn1. Our data suggest that PSD‐95 interacts with NBCn1 and increases its channel‐like activity while negligibly affecting Na/HCO3 cotransport. We propose that the channel‐like activity may occur via an intermolecular cavity of multimeric NBCn1 proteins.