Gregorio C C, Trombitás K, Centner T, Kolmerer B, Stier G, Kunke K, Suzuki K, Obermayr F, Herrmann B, Granzier H, Sorimachi H, Labeit S
Departments of Cell Biology and Anatomy, and Molecular and Cellular Biology, University of Arizona, Tucson, Arizona 85724, USA.
J Cell Biol. 1998 Nov 16;143(4):1013-27. doi: 10.1083/jcb.143.4.1013.
Titin is a giant elastic protein in vertebrate striated muscles with an unprecedented molecular mass of 3-4 megadaltons. Single molecules of titin extend from the Z-line to the M-line. Here, we define the molecular layout of titin within the Z-line; the most NH2-terminal 30 kD of titin is located at the periphery of the Z-line at the border of the adjacent sarcomere, whereas the subsequent 60 kD of titin spans the entire width of the Z-line. In vitro binding studies reveal that mammalian titins have at least four potential binding sites for alpha-actinin within their Z-line spanning region. Titin filaments may specify Z-line width and internal structure by varying the length of their NH2-terminal overlap and number of alpha-actinin binding sites that serve to cross-link the titin and thin filaments. Furthermore, we demonstrate that the NH2-terminal titin Ig repeats Z1 and Z2 in the periphery of the Z-line bind to a novel 19-kD protein, referred to as titin-cap. Using dominant-negative approaches in cardiac myocytes, both the titin Z1-Z2 domains and titin-cap are shown to be required for the structural integrity of sarcomeres, suggesting that their interaction is critical in titin filament-regulated sarcomeric assembly.
肌联蛋白是脊椎动物横纹肌中的一种巨大弹性蛋白，分子量高达300 - 400万道尔顿，前所未见。肌联蛋白单分子从Z线延伸至M线。在此，我们确定了肌联蛋白在Z线内的分子布局；肌联蛋白最靠近氨基端的30kD位于相邻肌节边界处Z线的周边，而随后的60kD则跨越Z线的整个宽度。体外结合研究表明，哺乳动物肌联蛋白在其跨越Z线的区域内至少有四个与α - 辅肌动蛋白的潜在结合位点。肌联蛋白丝可能通过改变其氨基端重叠长度和用于交联肌联蛋白与细肌丝的α - 辅肌动蛋白结合位点数量来确定Z线宽度和内部结构。此外，我们证明Z线周边的肌联蛋白氨基端免疫球蛋白重复序列Z1和Z2与一种新的19kD蛋白结合，该蛋白称为肌联蛋白帽。在心肌细胞中采用显性负性方法，结果表明肌节的结构完整性需要肌联蛋白Z1 - Z2结构域和肌联蛋白帽，这表明它们之间的相互作用在肌联蛋白丝调节的肌节组装中至关重要。
