Oxidation of the skeletal muscle Ca2+ release channel alters calmodulin binding

This study presents evidence for a close relationship between the oxidation state of the skeletal muscle Ca2+ release channel (RyR1) and its ability t o bind calmodulin (CaM). CaM enhances the activity of RyR1 in low Ca2+ and inhibits its activity in high Ca2+. Oxidation, which activates the channel, blocks the binding of I-125-labeled CaM at both micromolar and nanomolar C a2+ concentrations. Conversely, bound CaM slows oxidation-induced cross-lin king between subunits of the RyR1 tetramer. Alkylation of hyperreactive sul fhydryls (<3% of the total sulfhydryls) on RyR1 with N-ethylmaleimide compl etely blocks oxidant-induced intersubunit cross-linking and inhibits Ca2+-f ree I-125-CaM but not Ca2+/I-125-CaM binding. These studies suggest that I) the sites on RyR1 for binding apocal-modulin have features distinct from t hose of the Ca2+/CaM site, 2) oxidation may alter the activity of RyR1 in p art by altering its interaction with CaM, and 3) CaM may protect RyR1 from oxidative modifications during periods of oxidative stress.