Noguchi J, Yanagisawa M, Imamura M, Kasuya Y, Sakurai T, Tanaka T, Masaki T
Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki, Japan.
J Biol Chem. 1992 Oct 5;267(28):20302-10.
M-Protein (165 kDa) is a structural constituent of myofibrillar M-band in striated muscle. We generated a monoclonal antibody which recognized a 165-kDa protein from chicken pectoralis muscle in immunoblot analysis and stained the M-band under immunofluorescence microscopy. By screening a lambda gt11 cDNA library from chicken embryonic pectoralis muscle with this antibody, we isolated a cDNA clone encoding the M-protein. Northern blot analysis showed that M-protein mRNA is expressed in pectoralis and cardiac muscle but not in gizzard smooth muscle or non-muscle tissues. Moreover, the anterior latissimus dorsi muscle, which consists almost exclusively of slow fiber types, contains no detectable levels of the mRNA. The full-length cDNA sequence predicted a 1,450-amino acid polypeptide with a calculated molecular weight of 163 x 10(3). The encoded protein contains several copies of two different repetitive motifs: five copies of fibronectin type III repeats are in the middle part of the predicted molecule, and two and four copies of the immunoglobulin C2-type repeats are located toward the NH2-terminal and COOH-terminal regions, respectively. This indicates that M-protein, along with other thick filament-associated proteins such as C-protein, twichin, and titin, belongs to the superfamily of cytoskeletal proteins with immunoglobulin/fibronectin repeats.
M蛋白（165 kDa）是横纹肌肌原纤维M带的一种结构成分。我们制备了一种单克隆抗体，该抗体在免疫印迹分析中可识别来自鸡胸大肌的165-kDa蛋白，并在免疫荧光显微镜下对M带进行染色。用该抗体筛选鸡胚胸大肌的λgt11 cDNA文库，我们分离出了一个编码M蛋白的cDNA克隆。Northern印迹分析表明，M蛋白mRNA在胸大肌和心肌中表达，但在肌胃平滑肌或非肌肉组织中不表达。此外，几乎完全由慢肌纤维类型组成的背阔肌前部肌肉中未检测到该mRNA水平。全长cDNA序列预测出一个1450个氨基酸的多肽，计算分子量为163×10³。编码的蛋白质包含两种不同重复基序的多个拷贝：在预测分子的中部有五个纤连蛋白III型重复序列拷贝，在NH2末端和COOH末端区域分别有两个和四个免疫球蛋白C2型重复序列拷贝。这表明M蛋白与其他粗肌丝相关蛋白如C蛋白、肌联蛋白和肌巨蛋白一样，属于具有免疫球蛋白/纤连蛋白重复序列的细胞骨架蛋白超家族。
