Higgins D G, Labeit S, Gautel M, Gibson T J
European Molecular Biology Laboratory, Heidelberg, Germany.
J Mol Evol. 1994 Apr;38(4):395-404. doi: 10.1007/BF00163156.
Titin and twitchin are giant proteins expressed in muscle. They are mainly composed of domains belonging to the fibronectin class III and immunoglobulin c2 families, repeated many times. In addition, both proteins have a protein kinase domain near the C-terminus. This paper explores the evolution of these and related muscle proteins in an attempt to determine the order of events that gave rise to the different repeat patterns and the order of appearance of the proteins. Despite their great similarity at the level of sequence organization, titin and twitchin diverged from each other at least as early as the divergence between vertebrates and nematodes. Most of the repeating units in titin and twitchin were estimated to derive from three original domains. Chicken smooth-muscle myosin light-chain kinase (smMLCK) also has a kinase domain, several immunoglobulin domains, and a fibronectin domain. From a comparison of the kinase domains, titin is predicted to have appeared first during the evolution of the family, followed by twitchin and with the vertebrate MLCKs last to appear. The so-called C-protein from chicken is also a member of this family but has no kinase domain. Its origin remains unclear but it most probably pre-dates the titin/twitchin duplication.
肌联蛋白和肌动蛋白结合蛋白是在肌肉中表达的巨大蛋白质。它们主要由属于纤连蛋白III类和免疫球蛋白c2家族的结构域组成，这些结构域重复多次。此外，这两种蛋白质在C末端附近都有一个蛋白激酶结构域。本文探讨了这些及相关肌肉蛋白的进化，试图确定产生不同重复模式的事件顺序以及这些蛋白质出现的顺序。尽管肌联蛋白和肌动蛋白结合蛋白在序列组织水平上非常相似，但它们至少在脊椎动物和线虫分化时就彼此分化了。据估计，肌联蛋白和肌动蛋白结合蛋白中的大多数重复单元源自三个原始结构域。鸡平滑肌肌球蛋白轻链激酶（smMLCK）也有一个激酶结构域、几个免疫球蛋白结构域和一个纤连蛋白结构域。通过对激酶结构域的比较，预计肌联蛋白在该家族进化过程中首先出现，其次是肌动蛋白结合蛋白，最后出现的是脊椎动物的肌球蛋白轻链激酶。鸡的所谓C蛋白也是这个家族的成员，但没有激酶结构域。其起源尚不清楚，但很可能早于肌联蛋白/肌动蛋白结合蛋白的复制。
