A single amino acid substitution in MDEG2 specifically alters desensitization of the proton-activated cation current

To clarify functional roles of MDEG2 (mammalian degenerin-2), a modulatory subunit of proton-activated cation channels, in MDEG1/MDEG2 heteromer, we replaced the Gly481 residue in MDEG2 with cysteine or phenylalanine and characterized them electrophysiologically. Expression of MDEG1 in Xenopus oocytes elicited proton-activated cation currents that were rapidly desensitized. Co-expression of MDEG1 and MDEG2 (or MDEG2-G481C) displayed similar current traces as MDEG1 alone. In contrast, co-expression of MDEG1 and MDEG2-G481F dramatically attenuated desensitization of the proton-activated currents. Interestingly, the G481F mutation in MDEG2 did not alter other channel properties including maximal whole-cell currents, ionic selectivity, pH-sensitivity and affinity for amiloride. Thus, Gly481 in MDEG2 specifically controls inactivation process of the MDEG1/MDEG2 channel.