Unphosphorylated twitchin forms a complex with actin and myosin that may contribute to tension maintenance in catch
Unphosphorylated twitchin forms a complex with actin and myosin that may contribute to tension maintenance in catch
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DOI：
10.1242/jeb.008722
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发表时间：
2007-12-15
影响因子：
2.8
通讯作者：
Watabe, Shugo
中科院分区：
文献类型：
--
作者：
Funabara, Daisuke;Hamamoto, Chieko;Watabe, Shugo
软体动物的平滑肌肉可以在较长的时间内保持张力，而能量消耗很少，这一过程被称为捕捉。Catch被认为是通过粗丝蛋白twitin的磷酸化来调节的，并涉及两个磷酸化位点，D1和D2，分别靠近N和C末端。本研究旨在探讨D2位点及其磷酸化在CATCH机制中的作用。构建了一个含有D2位点和侧翼免疫球蛋白(Ig)基序的多肽。结果表明，去磷酸化的多肽与肌动蛋白和肌球蛋白结合，而不是磷酸化形式。肌动蛋白的结合部位在序列L10至P29内。该区域还与肌球蛋白头部的环2结合。去磷酸化的多肽连接了肌球蛋白和F-肌动蛋白，形成了一个三聚体复合体。电子显微镜观察发现，肌动蛋白分布在粗丝表面，轴向周期为36.25 nm，提示D2位点与肌球蛋白头部对齐。推测Twitin、F-肌动蛋白和肌球蛋白去磷酸化的D2位点形成的复合体是CATCH中机械连接的一个组成部分。
Molluscan smooth muscle can maintain tension over extended periods with little energy expenditure, a process termed catch. Catch is thought to be regulated by phosphorylation of a thick filament protein, twitchin, and involves two phosphorylation sites, D1 and D2, close to the N and C termini, respectively. This study was initiated to investigate the role of the D2 site and its phosphorylation in the catch mechanism. A peptide was constructed containing the D2 site and flanking immunoglobulin (Ig) motifs. It was shown that the dephosphorylated peptide, but not the phosphorylated form, bound to both actin and myosin. The binding site on actin was within the sequence L10 to P29. This region also binds to loop 2 of the myosin head. The dephosphorylated peptide linked myosin and F-actin and formed a trimeric complex. Electron microscopy revealed that twitchin is distributed on the surface of the thick filament with an axial periodicity of 36.25 nm and it is suggested that the D2 site aligns with the myosin heads. It is proposed that the complex formed with the dephosphorylated D2 site of twitchin, F-actin and myosin represents a component of the mechanical linkage in catch.