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dystrophin
Dystrophin is a rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane. This complex is variously known as the costamere or the dystrophin-associated protein complex. Many muscle proteins, such as α-dystrobrevin, syncoilin, synemin, sarcoglycan, dystroglycan, and sarcospan, colocalize with dystrophin at the costamere.
The dystrophin gene is one of the longest human genes known, covering 2.5 megabases (0.08% of the human genome) at locus Xp21. The primary transcript measures about 2,400 kilobases and takes 16 hours to transcribe; the mature mRNA measures 14.0 kilobases.〔(NCBI Sequence Viewer v2.0 )〕 The 79 exons〔Strachan T and Read AP, 1999. Human molecular genetics, BIOS Scientific, New York, USA〕 code for a protein of over 3500 amino acid residues.〔(NCBI Sequence Viewer v2.0 )〕
== Function ==
Dystrophin is a protein located between the sarcolemma and the outermost layer of myofilaments in the muscle fiber (myofiber). It is a cohesive protein, linking actin filaments to another support protein that resides on the inside surface of each muscle fiber’s plasma membrane (sarcolemma). This support protein on the inside surface of the sarcolemma in turn links to two other consecutive proteins for a total of three linking proteins. The final linking protein is attached to the fibrous endomysium of the entire muscle fiber. Dystrophin supports muscle fiber strength, and the absence of dystrophin reduces muscle stiffness, increases sarcolemmal deformability, and compromises the mechanical stability of costameres and their connections to nearby myofibrils; as shown in recent studies where biomechanical properties of the sarcolemma and its links through costameres to the contractile apparatus were measured, and helps to prevent muscle fiber injury. Movement of thin filaments (actin) creates a pulling force on the extracellular connective tissue that eventually becomes the tendon of the muscle.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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