27] Methylated lysines and 3-methylhistidine in myosin: Tissue and developmental differences

Abstract

Publisher Summary This chapter deals with tissue and developmental differences in methylated lysines and 3-methylhistidine (3-MeHis) in myosin. Four different methylated amino acids have been identified in myosins—namely, 3-MeHis, ɛ - N -monomethyllysine (MeLys), ɛ - N -dimethyllysine (Me 2 Lys), and ɛ - N -trimethyllysine (Me 3 Lys). All these unusual residues are in the heavy chain of subfragment 1, the globular head of myosin that carries the sites for ATP hydrolysis and actin combination. Distribution of methylated amino acids is investigated by isolating and sequencing the peptides which contain the 3-MeHis and the two Me 3 Lys in rabbit fast skeletal muscle myosin. Both 3-MeHis and Me 3 Lys are present as fully methylated and trimethylated amino acids in the myosin heavy chain, and there are no partially methylated Lys and His residues. The 3-MeHis containing tryptic peptide contains 13 amino acid residues, including the methylated histidine. The methylated amino acids, like other amino acids, are analyzed in the HCl hydrolyzates of proteins. Similar to other posttranslational amino acid side-chain modifications, lysines and histidines are enzymatically methylated after they are incorporated into the myosin peptide chain. The methyl donor is S -adenosyl-L-methionine (SAM). Methylation of myosin with SAM donors has been carried out in various experimental designs such as in muscle homogenates and cultures, in perfused hearts, and by in vitro methylation of nascent myosin chains still attached to polyribosomes.