Yuan Chen-Ching, Ma Weikang, Schemmel Peter, Cheng Yu-Shu, Liu Jiangmin, Tsaprailis George, Feldman Samuel, Ayme Southgate Agnes, Irving Thomas C
Dept. of Biological and Chemical Sciences, Illinois Institute of Technology, 3101 S. Dearborn St., Chicago, IL 60616, USA.
Center for Toxicology, University of Arizona, Tucson, AZ, USA.
Arch Biochem Biophys. 2015 Feb 15;568:16-27. doi: 10.1016/j.abb.2014.12.033. Epub 2015 Jan 17.
The flight muscles (DLM1) of the Hawkmoth, Manduca sexta are synchronous, requiring a neural spike for each contraction. Stress/strain curves of skinned DLM1 showed hysteresis indicating the presence of titin-like elastic proteins. Projectin and kettin are titin-like proteins previously identified in Lethocerus and Drosophila flight muscles. Analysis of Manduca muscles with 1% SDS-agarose gels and western blots showed two bands near 1 MDa that cross-reacted with antibodies to Drosophila projectin. Antibodies to Drosophila kettin cross-reacted to bands at ∼500 and ∼700 kDa, but also to bands at ∼1.6 and ∼2.1 MDa, that had not been previously observed in insect flight muscles. Mass spectrometry identified the 2.1 MDa protein as a product of the Sallimus (sls) gene. Analysis of the gene sequence showed that all 4 putative Sallimus and kettin isoforms could be explained as products of alternative splicing of the single sls gene. Both projectin and sallimus isoforms were expressed to higher levels in ventrally located DLM1 subunits, primarily responsible for active work production, as compared to dorsally located subunits, which may act as damped springs. The different expression levels of the 2 projectin isoforms and 4 sallimus/kettin isoforms may be adaptations to the specific requirements of individual muscle subunits.
烟草天蛾（Manduca sexta）的飞行肌肉（DLM1）是同步性的，每次收缩都需要一个神经冲动。去除肌膜的DLM1的应力/应变曲线显示出滞后现象，表明存在类肌联蛋白弹性蛋白。肌联蛋白和伴肌动蛋白是先前在大田鳖和果蝇飞行肌肉中鉴定出的类肌联蛋白。用1% SDS-琼脂糖凝胶和蛋白质免疫印迹法分析烟草天蛾肌肉，结果显示在1 MDa附近有两条带与果蝇肌联蛋白抗体发生交叉反应。果蝇伴肌动蛋白抗体与约500 kDa和约700 kDa的条带发生交叉反应，但也与约1.6 MDa和约2.1 MDa的条带发生交叉反应，而这些条带在昆虫飞行肌肉中以前未曾观察到。质谱分析确定2.1 MDa的蛋白质是Sallimus（sls）基因的产物。对该基因序列的分析表明，所有4种假定的Sallimus和伴肌动蛋白异构体都可以解释为单个sls基因可变剪接的产物。与可能充当减震弹簧的背侧亚基相比，肌联蛋白和Sallimus异构体在主要负责产生主动功的腹侧DLM1亚基中表达水平更高。2种肌联蛋白异构体和4种Sallimus/伴肌动蛋白异构体的不同表达水平可能是对单个肌肉亚基特定需求的适应性表现。
