The dystrophin–glycan complex

A complex system of interconnected noncovalently
bound proteins in the sarcolemma
(plasma membrane) of muscle cells lends the
cell stability under the extreme exertion of contraction
and relaxation. They connect the extracellular
matrix and the intracellular myofibrils,
elongated protein molecules aligned in parallel
chains (myofilaments). The largest of the interconnected
proteins, !-dystroglycan (156 kDa),
is located outside the cell. It is connected to the
extracellular matrix by a heterotrimeric protein,
laminin-2. "-Dystroglycan (43 kDa) is embedded
in the sarcolemma and connected to a
series of other cytoskeletal proteins, which are
divided into the sarcoglycan and syntrophin
subcomplexes. Several members of the sarcoglycan
complex are related to specific types of
muscular dystrophies due to mutations in the
corresponding genes.
Dystrophin, a large, elongated protein, provides
a bridge between the intracellular cytoskeleton
involved in the contractile myofilaments and
the extracellular matrix. Two dystrophin
molecules connect neighboring dystrophin–
glycan complexes. The N-terminal end of dystrophin
is connected to the thinmyofilament Factin
(filamentous actin). The C-terminal end of
dystrophin is connected to "-dystroglycan and
the syntrophins.