Tzolovsky George, Millo Hadas, Pathirana Stephen, Wood Timothy, Bownes Mary
Institute of Cell and Molecular Biology, University of Edinburgh.
Mol Biol Evol. 2002 Jul;19(7):1041-52. doi: 10.1093/oxfordjournals.molbev.a004163.
Myosins constitute a superfamily of motor proteins that convert energy from ATP hydrolysis into mechanical movement along the actin filaments. Phylogenetic analysis currently places myosins into 17 classes based on class-specific features of their conserved motor domain. Traditionally, the myosins have been divided into two classes depending on whether they form monomers or dimers. The conventional myosin of muscle and nonmuscle cells forms class II myosins. They are complex molecules of four light chains bound to two heavy chains that form bipolar filaments via interactions between their coiled-coil tails (type II). Class I myosins are smaller monomeric myosins referred to as unconventional myosins. Now, at least 15 other classes of unconventional myosins are known. How many myosins are needed to ensure the proper development and function of eukaryotic organisms? Thus far, three types of myosins were found in budding yeast, six in the nematode Caenorhabditis elegans, and at least 12 in human. Here, we report on the identification and classification of Drosophila melanogaster myosins. Analysis of the Drosophila genome sequence identified 13 myosin genes. Phylogenetic analysis based on the sequence comparison of the myosin motor domains, as well as the presence of the class-specific domains, suggests that Drosophila myosins can be divided into nine major classes. Myosins belonging to previously described classes I, II, III, V, VI, and VII are present. Molecular and phylogenetic analysis indicates that the fruitfly genome contains at least five new myosins. Three of them fall into previously described myosin classes I, VII, and XV. Another myosin is a homolog of the mouse and human PDZ-containing myosins, forming the recently defined class XVIII myosins. PDZ domains are named after the postsynaptic density, disc-large, ZO-1 proteins in which they were first described. The fifth myosin shows a unique domain composition and a low homology to any of the existing classes. We propose that this is classified when similar myosins are identified in other species.
肌球蛋白构成了一个马达蛋白超家族，该家族可将ATP水解产生的能量转化为沿肌动蛋白丝的机械运动。系统发育分析目前根据其保守马达结构域的类别特异性特征将肌球蛋白分为17类。传统上，肌球蛋白根据其形成单体还是二聚体分为两类。肌肉和非肌肉细胞中的传统肌球蛋白形成II类肌球蛋白。它们是由四条轻链与两条重链结合而成的复杂分子，通过其卷曲螺旋尾巴之间的相互作用形成双极丝（II型）。I类肌球蛋白是较小的单体肌球蛋白，被称为非传统肌球蛋白。现在，已知至少还有15类其他非传统肌球蛋白。真核生物的正常发育和功能需要多少种肌球蛋白？到目前为止，在芽殖酵母中发现了三种肌球蛋白，在秀丽隐杆线虫中发现了六种，在人类中至少发现了12种。在此，我们报告了黑腹果蝇肌球蛋白的鉴定和分类。对果蝇基因组序列的分析鉴定出13个肌球蛋白基因。基于肌球蛋白马达结构域的序列比较以及类别特异性结构域的存在进行的系统发育分析表明，果蝇肌球蛋白可分为九个主要类别。属于先前描述的I、II、III、V、VI和VII类的肌球蛋白都存在。分子和系统发育分析表明，果蝇基因组至少包含五种新的肌球蛋白。其中三种属于先前描述的I、VII和XV类肌球蛋白。另一种肌球蛋白是小鼠和人类含PDZ肌球蛋白的同源物，形成了最近定义的XVIII类肌球蛋白。PDZ结构域以其首次被描述的突触后致密物、盘状大蛋白、ZO-1蛋白命名。第五种肌球蛋白显示出独特的结构域组成，与任何现有类别都具有低同源性。我们建议在其他物种中鉴定出类似肌球蛋白时对其进行分类。
