Kollmar Martin
Abteilung NMR basierte Strukturbiologie, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, D-37077 Goettingen, Germany.
BMC Genomics. 2006 Jul 20;7:183. doi: 10.1186/1471-2164-7-183.
Dictyostelium discoideum is one of the most famous model organisms for studying motile processes like cell movement, organelle transport, cytokinesis, and endocytosis. Members of the myosin superfamily, that move on actin filaments and power many of these tasks, are tripartite proteins consisting of a conserved catalytic domain followed by the neck region consisting of a different number of so-called IQ motifs for binding of light chains. The tails contain functional motifs that are responsible for the accomplishment of the different tasks in the cell. Unicellular organisms like yeasts contain three to five myosins while vertebrates express over 40 different myosin genes. Recently, the question has been raised how many myosins a simple multicellular organism like Dictyostelium would need to accomplish all the different motility-related tasks.
The analysis of the Dictyostelium genome revealed thirteen myosins of which three have not been described before. The phylogenetic analysis of the motor domains of the new myosins placed Myo1F to the class-I myosins and Myo5A to the class-V myosins. The third new myosin, an orphan myosin, has been named MyoG. It contains an N-terminal extension of over 400 residues, and a tail consisting of four IQ motifs and two MyTH4/FERM (myosin tail homology 4/band 4.1, ezrin, radixin, and moesin) tandem domains that are separated by a long region containing an SH3 (src homology 3) domain. In contrast to previous analyses, an extensive comparison with 126 class-VII, class-X, class-XV, and class-XXII myosins now showed that MyoI does not group into any of these classes and should not be used as a model for class-VII myosins.The search for calmodulin related proteins revealed two further potential myosin light chains. One is a close homolog of the two EF-hand motifs containing MlcB, and the other, CBP14, phylogenetically groups to the ELC/RLC/calmodulin (essential light chain/regulatory light chain) branch of the tree.
Dictyostelium contains thirteen myosins together with 6-8 MLCs (myosin light chain) to assist in a variety of actin-based processes in the cell. Although they are homologous to myosins of higher eukaryotes, the myosins of Dictyostelium should be considered with care as models for specific functions of vertebrate myosins.
盘基网柄菌是研究细胞运动、细胞器运输、胞质分裂和胞吞作用等运动过程最著名的模式生物之一。肌球蛋白超家族成员在肌动蛋白丝上移动并为许多这些任务提供动力，它们是由一个保守的催化结构域、随后是由不同数量的所谓IQ模体组成的颈部区域（用于结合轻链）构成的三联体蛋白。尾部包含负责在细胞中完成不同任务的功能模体。像酵母这样的单细胞生物含有三到五种肌球蛋白，而脊椎动物表达超过40种不同的肌球蛋白基因。最近，有人提出像盘基网柄菌这样的简单多细胞生物需要多少种肌球蛋白才能完成所有与运动相关的不同任务。
对盘基网柄菌基因组的分析揭示了13种肌球蛋白，其中三种以前未曾描述过。对新肌球蛋白的运动结构域进行系统发育分析，将肌球蛋白1F归入I类肌球蛋白，将肌球蛋白5A归入V类肌球蛋白。第三种新的肌球蛋白是一种孤儿肌球蛋白，被命名为肌球蛋白G。它包含一个超过400个残基的N端延伸，以及一个由四个IQ模体和两个MyTH4/FERM（肌球蛋白尾部同源性4/带4.1、埃兹蛋白、根蛋白和膜突蛋白）串联结构域组成的尾部，这些结构域被一个包含SH3（src同源性3）结构域的长区域隔开。与之前的分析不同，现在与126种VII类、X类、XV类和XXII类肌球蛋白进行的广泛比较表明，肌球蛋白I不属于这些类别中的任何一类，不应被用作VII类肌球蛋白的模型。对钙调蛋白相关蛋白的搜索又发现了另外两种潜在的肌球蛋白轻链。一种是含有MlcB的两个EF手模体的紧密同源物，另一种是CBP14，在系统发育上归入树的ELC/RLC/钙调蛋白（必需轻链/调节轻链）分支。
盘基网柄菌含有13种肌球蛋白以及6 - 8种肌球蛋白轻链（MLC），以协助细胞中各种基于肌动蛋白的过程。尽管它们与高等真核生物的肌球蛋白同源，但盘基网柄菌的肌球蛋白作为脊椎动物肌球蛋白特定功能的模型时应谨慎考虑。
