Obscurin & Myofibrils in Cardiac & Skeletal Muscle

描述（由申请人提供）：近年来，我们已经了解了大量关于横膈膜中粗细细丝的组装，以及调节收缩周期所必需的Ca2+释放和再摄取的蛋白质。然而，对于将粗细细丝整合成肌原纤维的机制，以及在肌节周围如此有规律地组织肌浆网（SR）和横小管（t-）的蛋白质，我们知之甚少。最近发现的obscurin为解决这些问题提供了新的途径。

DESCRIPTION (provided by applicant): In recent years, we have learned a great deal about the assembly of thick and thin filaments in striated muscle, and about the proteins that regulate the release and re-uptake of Ca2+ essential for the contractile cycle. We know much less, however, about the mechanisms that integrate thick and thin filaments into myofibrils, and about the proteins that organize the sarcoplasmic reticulum (SR) and transverse (t-) tubules so regularly around sarcomere. The recent discovery of obscurin offers new ways to address these questions. Obscurin is an approximately 800 kDa protein with structural homology to titin. It is the only protein of the titin superfamily that is concentrated, at least in part, at the periphery of sarcomeres, primarily around M-lines and Z-disks. Obscurin is composed largely of tandem Ig domains but also has signaling domains and, at its extreme COOH-terminus, a binding site for a small, integral membrane form of ankyrin 1 that is concentrated in the network SR. Given its apparent ability to concentrate at the periphery of the myofibril around M-lines and Z-disks and its high affinity for an integral protein of the SR membrane, obscurin is ideally suited to play key roles in assembling and organizing both the sarcomere and the SR. We propose to test this general hypothesis through 4 specific aims: (1) to learn how obscurin is organized with respect to key structures within sarcomeres; (2) to learn how obscurin binds to elements in the contractile apparatus; (3) to assess the effect on morphogenesis of the myofibrils and associated membranes of altering the activity of obscurin with siRNA and thru adenoviral overexpression of particular binding domains; and (4) to investigate the role of obscurin's binding to small ankyrin 1 in the assembly, organization and function of the SR. Mutations in proteins of the contractile apparatus, including some that affect the assembly or stability of contractile elements, have been implicated in hypertrophic cardiomyopathies and muscular dystrophies. The results of our experiments should reveal some of the key mechanisms involved in assembling contractile proteins into sarcomeres and in determining their association with the SR.