Methionine Sulfoxide Reductase B1 (MsrB1) Recovers TRPM6 Channel Activity during Oxidative Stress

Mg2+ is an essential ion for many cellular processes, including protein synthesis, nucleic acid stability, and numerous enzymatic reactions. Mg2+ homeostasis in mammals depends on the equilibrium between intestinal absorption, renal excretion, and exchange with bone. The transient receptor potential melastatin type 6 (TRPM6) is an epithelial Mg2+ channel, which is abundantly expressed in the luminal membrane of the renal and intestinal cells. It functions as the gatekeeper of transepithelial Mg2+ transport. Remarkably, TRPM6 combines a Mg2+-permeable channel with an alpha-kinase domain. Here, by the Ras recruitment system, we identified methionine sulfoxide reductase B1 (MsrB1) as an interacting protein of the TRPM6 alpha-kinase domain. Importantly, MsrB1 and TRPM6 are both present in the renal Mg2+-transporting distal convoluted tubules. MsrB1 has no effect on TRPM6 channel activity in the normoxic conditions. However, hydrogen peroxide (H2O2) decreased TRPM6 channel activity. Co-expression of MsrB1 with TRPM6 attenuated the inhibitory effect of H2O2 (TRPM6, 67 +/- 5% of control; TRPM6 + MsrB1, 81 +/- 5% of control). Cell surface biotinylation assays showed that H2O2 treatment does not affect the expression of TRPM6 at the plasma membrane. Next, mutation of Met(1755) to Ala in TRPM6 reduced the inhibitory effect of H2O2 on TRPM6 channel activity (TRPM6 M1755A: 84 +/- 10% of control), thereby mimicking the action of MsrB1. Thus, these data suggest that MsrB1 recovers TRPM6 channel activity by reducing the oxidation of Met(1755) and could, thereby, function as a modulator of TRPM6 during oxidative stress.