Effects of S-glutathionylation and S-nitrosylation on calmodulin binding to triads and FKBP12 binding to type 1 calcium release channels.

This study shows that the combination of glutathione (GSH) plus hydrogen peroxide (H2O2) promotes the S-glutathionylation of ryanodine receptor type 1 (RyR1) Ca2+ release channels, and confirms their joint S-glutathionylation and S-nitrosylation by S-nitrosoglutathione (GSNO). In addition, we show that 35S-labeled 12-kDa FK506-binding protein ([35S]FKBP12) bound with a Kd of 13.1 nM to RyR1 present in triads or heavy sarcoplasmic reticulum vesicles; RyR1 S-nitrosylation by NOR-3 or GSNO, but not S-glutathionylation, specifically increased by four- to fivefold this Kd value. RyR1 redox modifications also increased the Kd of [35S]calmodulin binding to triads without affecting Bmax. RyR1 S-glutathionylation (induced by GSH plus H2O2) or RyR1 S-nitrosylation (produced by NOR-3) increased by approximately six- or twofold, respectively, the Kd of apocalmodulin (apoCaM) or Ca2+-calmodulin (CaCaM) binding to triads. Likewise, the combined S-glutathionylation and S-nitrosylation of RyR1 induced by GSNO increased by fourfold the Kd of CaCaM binding to triads and abolished apoCaM binding. As both FKBP12 and CaCaM inhibit RyR1, decreased FKBP12 binding to RyR1 and/or decreased CaCaM binding to either RyR1 or dihydropyridine receptor in triad preparations may cause the reported enhanced activation of Ca2+-induced Ca2+ release kinetics mediated by S-glutathionylation/S-nitrosylation. We discuss possible consequences of these redox modifications on RyR1-mediated Ca2+ release in physiological or pathological conditions.