Zuellig Richard A, Bornhauser Beat C, Amstutz Ralf, Constantin Bruno, Schaub Marcus C
Department of Endocrinology and Diabetes, University Hospital Zurich, 8091 Zurich, Switzerland.
J Biomed Biotechnol. 2011;2011:904547. doi: 10.1155/2011/904547. Epub 2011 Nov 14.
Utrophin and dystrophin present two large proteins that link the intracellular actin cytoskeleton to the extracellular matrix via the C-terminal-associated protein complex. Here we describe a novel short N-terminal isoform of utrophin and its protein product in various rat tissues (N-utro, 62 kDa, amino acids 1-539, comprising the actin-binding domain plus the first two spectrin repeats). Using different N-terminal recombinant utrophin fragments, we show that actin binding exhibits pronounced negative cooperativity (affinity constants K(1) = -5 × 10(6) and K(2) =-1 × 10(5 )M(-1)) and is Ca(2+)-insensitive. Expression of the different fragments in COS7 cells and in myotubes indicates that the actin-binding domain alone binds exclusively to actin filaments. The recombinant N-utro analogue binds in vitro to actin and in the cells associates to the membranes. The results indicate that N-utro may be responsible for the anchoring of the cortical actin cytoskeleton to the membranes in muscle and other tissues.
肌养蛋白和肌营养不良蛋白是两种大型蛋白质，它们通过C端相关蛋白复合物将细胞内肌动蛋白细胞骨架与细胞外基质相连。在此，我们描述了一种新型的肌养蛋白短N端异构体及其在多种大鼠组织中的蛋白质产物（N-肌养蛋白，62 kDa，氨基酸1-539，包含肌动蛋白结合结构域以及前两个血影蛋白重复序列）。使用不同的N端重组肌养蛋白片段，我们发现肌动蛋白结合表现出明显的负协同性（亲和常数K(1) = -5 × 10(6) 和K(2) = -1 × 10(5 )M(-1)）且对Ca(2+)不敏感。不同片段在COS7细胞和肌管中的表达表明，仅肌动蛋白结合结构域就专门与肌动蛋白丝结合。重组N-肌养蛋白类似物在体外与肌动蛋白结合，在细胞中与膜结合。结果表明，N-肌养蛋白可能负责肌肉和其他组织中皮质肌动蛋白细胞骨架与膜的锚定。
