Kranewitter W J, Ylanne J, Gimona M
Department of Cell Biology, Institute of Molecular Biology, Austrian Academy of Sciences, Billrothstrasse 11, A-5020 Salzburg, Austria.
J Biol Chem. 2001 Mar 2;276(9):6306-12. doi: 10.1074/jbc.M009561200. Epub 2000 Nov 28.
The Caenorhabditis elegans unc-87 gene product is essential for the maintenance of the nematode body wall muscle where it is found colocalized with actin in the I band. The molecular domain structure of the protein reveals similarity to the C-terminal repeat region of the smooth muscle actin-binding protein calponin. In this study we investigated the in vitro function of UNC-87 using both the full-length recombinant molecule and several truncated mutants. According to analytical ultracentrifugation UNC-87 occurs as a monomer in solution. UNC-87 cosedimented with both smooth and skeletal muscle F-actin, but not with monomeric G-actin, and exhibited potent actin filament bundling activity. Actin binding was independent of the presence of tropomyosin and the actin cross-linking proteins filamin and alpha-actinin. Consistent with its actin bundling activity in vitro, UNC-87 tagged with green fluorescent protein associated with and promoted the formation of actin stress fiber bundles in living cells. These data identify UNC-87 as an actin-bundling protein and highlight the calponin-like repeats as a novel actin-binding module.
秀丽隐杆线虫unc-87基因产物对于维持线虫体壁肌肉至关重要，在体壁肌肉中它与肌动蛋白共定位于I带。该蛋白质的分子结构域与平滑肌肌动蛋白结合蛋白钙调蛋白的C末端重复区域相似。在本研究中，我们使用全长重组分子和几个截短突变体研究了UNC-87的体外功能。根据分析超速离心结果，UNC-87在溶液中以单体形式存在。UNC-87与平滑肌和骨骼肌的F-肌动蛋白共沉降，但不与单体G-肌动蛋白共沉降，并表现出强大的肌动蛋白丝成束活性。肌动蛋白结合不依赖于原肌球蛋白以及肌动蛋白交联蛋白细丝蛋白和α-辅肌动蛋白的存在。与其体外肌动蛋白成束活性一致，用绿色荧光蛋白标记的UNC-87在活细胞中与肌动蛋白应力纤维束相关并促进其形成。这些数据将UNC-87鉴定为一种肌动蛋白成束蛋白，并突出了钙调蛋白样重复序列作为一种新的肌动蛋白结合模块。
