Loss of the Calmodulin-Dependent Inhibition of the RyR1 Calcium Release Channel upon Oxidation of Methionines in Calmodulin

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• 作者：Curt B. Boschek ; Terry E. Jones ; Heather S. Smallwood ; Thomas C. Squier ; Diana J. Bigelow
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：January 8, 2008
• 年：2008
• 卷：47
• 期：1
• 页码：131 - 142
• 全文大小：207K
• 年卷期：v.47,no.1(January 8, 2008)
• ISSN：1520-4995

文摘

The oxidation of methionines in calmodulin (CaM) can affect the activity of calcium pumpsand channels to modulate the amplitude and duration of calcium signals. We have therefore investigatedthe possible oxidation of CaM in skeletal muscle and its effect on the CaM-dependent regulation of theRyR1 calcium release channel. Taking advantage of characteristic reductions in electrophoretic mobilitydetermined by SDS-PAGE, we find that approximately two methionines are oxidized in CaM from skeletalmuscle. The functional effect of CaM oxidation on the open probability of the RyR1 calcium releasechannel was assessed through measurements of [³H]ryanodine binding using a heavy sarcoplasmic reticulumpreparation enriched in RyR1. There is a biphasic regulation of RyR1 by unoxidized CaM, in whichcalcium-activated CaM acts to enhance the calcium sensitivity of channel closure, while apo-CaM functionsto enhance channel activity at resting calcium levels. We find that physiological levels of CaM oxidationpreferentially weaken the CaM-dependent inhibition of the RyR1 calcium release channel observed atactivating micromolar levels of calcium. In contrast, the oxidation of CaM resulted in minimal functionalchanges in the CaM-dependent activation of RyR1 at resting nanomolar calcium levels. Oxidation doesnot significantly affect the high-affinity binding of calcium-activated CaM to the CaM-binding sequenceof RyR1; rather, methionine oxidation disrupts interdomain interactions between the opposing domainsof CaM in complex with the CaM-binding sequence of RyR1 that normally function as part of aconformational switch associated with RyR1 inhibition. These results suggest that the oxidation of CaMcan contribute to observed elevations in intracellular calcium levels in response to conditions of oxidativestress observed during biological aging. We suggest that the sensitivity of RyR1 channel activity to CaMoxidation may function as part of an adaptive cellular response that enhances the duration of calciumtransients to promote enhanced contractility.