The primary structure of the myosin head

Area of Science:

• Biochemistry
• Molecular Biology
• Muscle Physiology

Background:

• Myosin is a crucial motor protein in muscle contraction.
• Understanding myosin head structure is key to muscle function.
• The NH2-terminal region of myosin plays a significant role in its activity.

Purpose of the Study:

• To determine the amino acid sequence of the NH2-terminal 808 residues of chicken pectoralis muscle myosin head.
• To identify and characterize specific fragments and post-translational modifications within this region.

Main Methods:

• Isolation of 20-, 23-, and 50-kDa fragments from myosin subfragment 1 (S1) using gel filtration and anion-exchange chromatography.
• Complete sequencing of isolated fragments using conventional methods.
• Cyanogen bromide cleavage of S1 to obtain overlapping peptides for precise fragment ordering.
• Identification of methylated amino acid residues.

Main Results:

• The complete sequence of the NH2-terminal 808 amino acid residues was determined.
• The precise arrangement of 20-, 23-, and 50-kDa fragments within S1 was established, with 5 amino acids between the 50- and 20-kDa fragments.
• Four methylated amino acid residues were identified: epsilon-N-monomethyllysine (position 35), epsilon-N-trimethyllysine (positions 130 and 550), and 3-N-methylhistidine (position 754).

Conclusions:

• The study provides a detailed sequence map of the chicken myosin head's NH2-terminal region.
• The identified methylated amino acids represent important post-translational modifications potentially affecting myosin function.
• This detailed structural information contributes to a deeper understanding of muscle protein mechanics and regulation.