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Structure of myosin heavy chain in avian muscular dystrophy
Abstract:
We have studied the structure of myosin heavy chain (MHC) in the pectoralis muscle of genetically dystrophic (Connecticut Strain) and White Leghorn chicks. MHC was alkylated with N-ethylmaleimide, purified by Sepharose-4B chromatography, and cleaved with cyanogen bromide. The MHC CNBr peptides were analyzed by one-dimensional and two-dimensional isoelectric focusing/sodium dodecyl sulfate gradient gels and by amino acid sequencing. Specific changes were detected in the gel patterns which could be correlated with the loss of muscle function as measured by the exhaustion score (the ability of chicks to rise from a reclining position) in three experimental groups (exhaustion scores: less than 3, 10-20, greater than 30). We have also examined the amino acid sequence of a 3-methyl-histidine-containing peptide which originates from the 20-kDa fragment of pectoralis muscle MHC in dystrophic chicks: Val-Leu-Asn-Ala-Ser-Ala-Ile-Pro-Glu-Gly-*Gln-Phe-*Ile-Asp-Ser-Lys-Lys- Ala-Ser-Leu-Gln-Lys-Leu-Gly-Ser-Ile-Asp-Val-(Asp, 3-methylhistidine, Gln). Comparison of the homologous MHC sequences shows two positions at which MHC from dystrophic chicks differs from that of the White Leghorn chicks *(Glu----Gln and Met----Ile). Thus, both the peptide map and sequence analyses demonstrate that in avian muscular dystrophy an abnormal pectoralis MHC is synthesized. It is not yet clear whether the "dystrophic" MHC is a variant MHC or if it arises from the abnormal expression of an earlier developmental form (embryonic or neonatal) of pectoralis muscle MHC.
Insights
Researchers found abnormal pectoralis myosin heavy chain (MHC) in genetically dystrophic chicks. This structural change in muscle protein is linked to reduced muscle function and disease progression in avian muscular dystrophy.
Area of Science:
- Biochemistry
- Molecular Biology
- Animal Science
Background:
- Avian muscular dystrophy is a genetic condition affecting muscle function.
- Myosin heavy chain (MHC) is a critical protein in muscle contraction.
- Understanding MHC structure is key to elucidating disease mechanisms.
Purpose of the Study:
- To investigate structural differences in pectoralis muscle myosin heavy chain (MHC) between genetically dystrophic and healthy chicks.
- To correlate these structural changes with observed muscle function deficits.
Main Methods:
- Alkylation of MHC with N-ethylmaleimide.
- Purification of MHC using Sepharose-4B chromatography.
- Cleavage of MHC with cyanogen bromide.
- Analysis of MHC peptides using gel electrophoresis and amino acid sequencing.
Main Results:
- Specific alterations in MHC peptide patterns were observed in dystrophic chicks.
- These changes correlated with reduced muscle function (exhaustion scores).
- Amino acid sequencing revealed two specific differences in MHC sequence between dystrophic and healthy chicks.
Conclusions:
- Genetically dystrophic chicks synthesize an abnormal pectoralis MHC.
- The observed structural abnormalities in MHC are associated with avian muscular dystrophy.
- Further research is needed to determine if the abnormal MHC is a variant or due to altered gene expression.