Loss of the Calmodulin-Dependent Inhibition of RyR1 Calcium Release Channel Upon Oxidation of Methionines in Calmodulin
Journal Article
·
· Biochemistry, 47(1):131-142
The oxidation of methionines in calmodulin (CaM) can affect the activity of calcium pumps and channels to modulate the amplitude and duration of calcium signals. We have therefore investigated the possible oxidation of CaM in skeletal muscle and its affect on the CaM-dependent regulation of the RyR1 calcium release channel. Taking advantage of characteristic reductions in electrophoretic mobility by SDS-PAGE, we find that approximately two methionines are oxidized in CaM from skeletal muscle. The functional effect of CaM oxidation on the open probability of the RyR1 calcium release channel was assessed through measurements of 3[H]-ryanodine binding using a heavy sarcoplasmic reticulum preparation enriched in RyR1. There is a biphasic regulation of RyR1 by unoxidized CaM, where calcium-activated CaM acts to enhance the calcium-sensitivity of channel closure, while apo-CaM functions to enhance channel activity at resting calcium levels. We find that physiological levels of CaM oxidation preferentially diminish the CaM-dependent inhibition of the RyR1 calcium release channel observed at activating micromolar levels of calcium. In contrast, the oxidation of CaM resulted in a minimal functional changes in the CaM-dependent activation of RyR1 at resting nanomolar calcium levels. Oxidation does not affect the high-affinity binding of calcium-activated CaM to the CaM-binding sequence of RyR1; rather, methionine oxidation disrupts interdomain interactions between the opposing domains of CaM in complex with the CaM-binding sequence of RyR1 that normally function as a conformational switch associated with RyR1 inhibition. These results suggest that the oxidation of CaM can contribute to observed elevations in intracellular calcium levels in response to conditions of oxidative stress. We suggest that the sensitivity of RyR1 channel activity to CaM oxidation may function as part of an adaptive cellular response to enhance the duration of calcium transients to promote enhanced contractility.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 922159
- Report Number(s):
- PNNL-SA-56189
- Journal Information:
- Biochemistry, 47(1):131-142, Journal Name: Biochemistry, 47(1):131-142 Journal Issue: 1 Vol. 47
- Country of Publication:
- United States
- Language:
- English
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