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Dystrophin-glycoprotein complex is highly enriched in isolated skeletal muscle sarcolemma
K Ohlendieck1, J M Ervasti, J B Snook
1Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City 52242.
Abstract:
mAbs specific for protein components of the surface membrane of rabbit skeletal muscle have been used as markers in the isolation and characterization of skeletal muscle sarcolemma membranes. Highly purified sarcolemma membranes from rabbit skeletal muscle were isolated from a crude surface membrane preparation by wheat germ agglutination. Immunoblot analysis of subcellular fractions from skeletal muscle revealed that dystrophin and its associated glycoproteins of 156 and 50 kD are greatly enriched in purified sarcolemma vesicles. The purified sarcolemma was also enriched in novel sarcolemma markers (SL45, SL/TS230) and Na+/K(+)-ATPase, whereas t-tubule markers (alpha 1 and alpha 2 subunits of dihydropyridine receptor, TS28) and sarcoplasmic reticulum markers (Ca2(+)-ATPase, ryanodine receptor) were greatly diminished in this preparation. Analysis of isolated sarcolemma by SDS-PAGE and densitometric scanning demonstrated that dystrophin made up 2% of the total protein in the rabbit sarcolemma preparation. Therefore, our results demonstrate that although dystrophin is a minor muscle protein it is a major constituent of the sarcolemma membrane in skeletal muscle. Thus the absence of dystrophin in Duchenne muscular dystrophy may result in a major disruption of the cytoskeletal network underlying the sarcolemma in dystrophic muscle.
Insights
Monoclonal antibodies aided in isolating rabbit skeletal muscle sarcolemma. Dystrophin, though a minor protein, is a major sarcolemma constituent, crucial for cytoskeletal integrity.
Area of Science:
- Muscle physiology
- Cellular membrane biology
- Biochemistry
Background:
- Sarcolemma membrane isolation and characterization are vital for understanding muscle function.
- Dystrophin's role in skeletal muscle structure and disease is under investigation.
Purpose of the Study:
- To isolate and characterize highly purified sarcolemma membranes from rabbit skeletal muscle.
- To determine the enrichment of dystrophin and other markers in the purified sarcolemma.
Main Methods:
- Wheat germ agglutination for sarcolemma purification.
- Immunoblot analysis and SDS-PAGE for protein characterization.
- Densitometric scanning to quantify protein composition.
Main Results:
- Purified sarcolemma vesicles were highly enriched in dystrophin and associated glycoproteins.
- Novel sarcolemma markers (SL45, SL/TS230) and Na+/K(+)-ATPase were enriched.
- T-tubule and sarcoplasmic reticulum markers were diminished, indicating high purity.
- Dystrophin constituted 2% of the total protein in the purified sarcolemma.
Conclusions:
- Dystrophin is a major component of the skeletal muscle sarcolemma, despite being a minor muscle protein.
- The absence of dystrophin in Duchenne muscular dystrophy likely causes significant disruption to the underlying cytoskeletal network.