Localization in the II-III loop of the dihydropyridine receptor of a sequence critical for excitation-contraction coupling
Localization in the II-III loop of the dihydropyridine receptor of a sequence critical for excitation-contraction coupling
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DOI：
10.1074/jbc.273.39.24983
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发表时间：
1998-09-25
影响因子：
4.8
通讯作者：
Beam, KG
中科院分区：
文献类型：
--
作者：
Nakai, J;Tanabe, T;Beam, KG
骨骼肌和心肌表达不同亚型的二氢吡啶受体(DHPR)，DHPR是一种电压门控钙离子通道，对兴奋-收缩(EC)偶联至关重要。然而，骨骼肌型EC偶联并不需要钙离子通过该通道进入。以前的工作(Tanabe，T.，Beam，K.G.，Adams，B.A.，Niidome，T.和Numa，S.(1990)Nature 346,567-569)揭示了重复序列II和III之间的环(II-III环)是骨架型EC偶联的重要决定因素。在本研究中，我们通过在发育不良的肌管中表达cDNAs结构，进一步剖析了对于骨架型EC偶联至关重要的II-III环区域。由于骨骼II-III环的Ser(687)已被报道在体外被快速磷酸化，我们用相应的心脏残基丙氨酸取代了这一丝氨酸。这种丙氨酸取代的骨架DHPR保留了介导骨架型EC偶联的能力。弱的骨架型EC偶联是由嵌合的DHPR产生的，除了II-III环中的少量骨架序列(残基725-742)外，它完全是心脏的。当残基725-742和相邻残基都是骨架时(例如，包含骨架残基711-765的嵌合体)，骨架类型耦合更强。然而，残基725-742似乎是关键的，因为骨架型偶联既不是由含有骨架残基711-732的嵌合体产生的，也不是由含有骨架残基734-765的嵌合体产生的。
Skeletal and cardiac muscles express distinct isoforms of the dihydropyridine receptor (DHPR), a type of voltage-gated Ca2+ channel that is important for excitation-contraction (EC) coupling. However, entry of Ca2+ through the channel is not required for skeletal muscle-type EC coupling. Previous work (Tanabe, T., Beam, K. G., Adams, B. A., Niidome, T., and Numa, S. (1990) Nature 346, 567-569) revealed that the loop between repeats II and III (II-III loop) is an important determinant of skeletal-type EC coupling. In the present study we have further dissected the regions of the II-III loop critical for skeletal-type EC coupling by expression of cDNA constructs in dysgenic myotubes. Because Ser(687) of the skeletal II-III loop has been reported to be rapidly phosphorylated in vitro, we substituted this serine with alanine, the corresponding cardiac residue. This alanine-substituted skeletal DHPR retained the ability to mediate skeletal-type EC coupling. Weak skeletal-type EC coupling was produced by a chimeric DHPR, which was entirely cardiac except for a small amount of skeletal sequence (residues 725-742) in the II-III loop. Skeletal-type coupling was stronger when both residues 725-742 and adjacent residues were skeletal (e.g. a chimera containing skeletal residues 711-765). However, residues 725-742 appeared to be critical because skeletal-type coupling was not produced either by a chimera with skeletal residues 711-732 or by one with skeletal residues 734-765.