Davis Dawn Belt, Doherty Katherine R, Delmonte Anthony J, McNally Elizabeth M
Department of Pathology, The University of Chicago, Chicago, Illinois 60637, USA.
J Biol Chem. 2002 Jun 21;277(25):22883-8. doi: 10.1074/jbc.M201858200. Epub 2002 Apr 16.
Mutations in dysferlin, a novel membrane protein of unknown function, lead to muscular dystrophy. Myoferlin is highly homologous to dysferlin and like dysferlin is a plasma membrane protein with six C2 domains highly expressed in muscle. C2 domains are found in a variety of membrane-associated proteins where they have been implicated in calcium, phospholipid, and protein-binding. We investigated the pattern of dysferlin and myoferlin expression in a cell culture model of muscle development and found that dysferlin is expressed in mature myotubes. In contrast, myoferlin is highly expressed in elongated "prefusion" myoblasts and is decreased in mature myotubes where dysferlin expression is greatest. We tested ferlin C2 domains for their ability to bind phospholipid in a calcium-sensitive manner. We found that C2A, the first C2 domain of dysferlin and myoferlin, bound 50% phosphatidylserine and that phospholipid binding was regulated by calcium concentration. A dysferlin point mutation responsible for muscular dystrophy was engineered into the dysferlin C2A domain and demonstrated reduced calcium-sensitive phospholipid binding. Based on these data, we propose a mechanism for muscular dystrophy in which calcium-regulated phospholipid binding is abnormal, leading to defective maintenance and repair of muscle membranes.
dysferlin（一种功能未知的新型膜蛋白）的突变会导致肌肉萎缩症。肌铁蛋白与dysferlin高度同源，并且和dysferlin一样是一种质膜蛋白，在肌肉中高表达，含有六个C2结构域。C2结构域存在于多种膜相关蛋白中，与钙、磷脂和蛋白质结合有关。我们在肌肉发育的细胞培养模型中研究了dysferlin和肌铁蛋白的表达模式，发现dysferlin在成熟肌管中表达。相比之下，肌铁蛋白在伸长的“融合前”成肌细胞中高表达，而在dysferlin表达量最高的成熟肌管中表达量降低。我们测试了ferlin C2结构域以钙敏感方式结合磷脂的能力。我们发现，dysferlin和肌铁蛋白的第一个C2结构域C2A能结合50%的磷脂酰丝氨酸，并且磷脂结合受钙浓度调节。将一个导致肌肉萎缩症的dysferlin点突变引入dysferlin C2A结构域，结果显示其钙敏感的磷脂结合能力降低。基于这些数据，我们提出了一种肌肉萎缩症的发病机制，即钙调节的磷脂结合异常，导致肌膜维持和修复缺陷。
