Evidence for periodicity in the amino-acid sequence of myosin

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Myosin heavy chain is a critical component of muscle fibers.
• Understanding its structure is key to muscle function.
• Previous studies have explored myosin fragmentation but not this specific periodicity.

Purpose of the Study:

• To investigate the fragmentation pattern of myosin heavy chain and related proteins.
• To identify any periodicities in the resulting fragments.
• To explore the implications of these periodicities for protein structure and sequence.

Main Methods:

• Chemical cleavage of rabbit and mouse myosin heavy chain using cyanogen bromide (CNBr).
• Analysis of fragments using combined isoelectric focusing and dodecylsulfate gel electrophoresis.
• Controlled digestion conditions to limit cleavage at methionine residues.

Main Results:

• A remarkable periodicity was observed in the molecular weights of fragments across multiple myosin digests.
• Fragments consistently appeared in a sequence with an approximate interval of 3800 Da.
• Periodicity was also noted in the isoelectric focusing dimension, suggesting ordered distribution of charged residues.

Conclusions:

• The observed periodicity strongly suggests a regular arrangement of methionine residues in myosin heavy chain, particularly in the light meromyosin region.
• The data indicates a potential underlying periodicity in the distribution of charged amino acids.
• These findings offer new insights into the structural organization of myosin heavy chain.