Molecular basis of calmodulin tethering and Ca2+-dependent inactivation of L-type Ca2+ channels

被引:237
作者
Pitt, GS
Zühlke, RD
Hudmon, A
Schulman, H
Reuter, H
Tsien, RW
机构
[1] Stanford Univ, Sch Med, Dept Cellular & Mol Physiol, Stanford, CA 94305 USA
[2] Stanford Univ, Sch Med, Dept Neurobiol, Stanford, CA 94305 USA
[3] Univ Bern, Dept Pharmacol, CH-3010 Bern, Switzerland
关键词
D O I
10.1074/jbc.M104959200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Ca2+-dependent inactivation (CDI) of L-type Ca2+ channels plays a critical role in controlling Ca2+ entry and downstream signal transduction in excitable cells. Ca2+-insensitive forms of calmodulin (CaM) act as dominant negatives to prevent CDI, suggesting that CaM acts as a resident Ca2+ sensor. However, it is not known how the Ca2+ sensor is constitutively tethered. We have found that the tethering of Ca2+-insensitive CaM was localized to the C-terminal tail of arc, close to the CDI effector motif, and that it depended on nanomolar Ca2+ concentrations, likely attained in quiescent cells. Two stretches of amino acids were found to support the tethering and to contain putative CaM-binding sequences close to or overlapping residues previously shown to affect CDI and Ca2+-independent inactivation. Synthetic peptides containing these sequences displayed differences in CaM-binding properties, both in affinity and Ca2+ dependence, leading us to propose a novel mechanism for CDI. In contrast to a traditional disinhibitory scenario, we suggest that apoCaM is tethered at two sites and signals actively to slow inactivation. When the C-terminal lobe of CaM binds to the nearby CaM effector sequence (IQ motif), the braking effect is relieved, and CDI is accelerated.
引用
收藏
页码:30794 / 30802
页数:9
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