title: Protease-sensitive regions in myosin subfragment 1.
abstract: Proteolytic digestions of myosin subfragment 1 (S-1) with elastase, subtilisin, papain, thermolysin, and Staphylococcus aureus protease reveal that the two trypsin-sensitive regions in S-1 have broad protease susceptibility. The cleavage of S-1 by these enzymes yields products that correspond within 1-2 kilodaltons (kDa) to the 25-, 50-, and 20-kDa fragments produced by trypsin. Papain and thermolysin cut preferentially at the 26-kDa/70-kDa junction, whereas elastase, subtilisin, and S. aureus protease cleave both the 26-kDa/70-kDa and 75-kDa/22-kDa junctions in S-1. Binding of actin to S-1 decreases the rate of all proteolytic reactions in the 95-kDa heavy chain. The protection of the 26-kDa/70-kDa junction by actin is greatest against papain and thermolysin attack. The reaction times of elastase, subtilisin, and S. aureus protease with S-1 increase 2-fold in the presence of actin. However, in contrast to similar reactions with trypsin, they proceed at both junctions and lead to formation of the 50- and 22-kDa fragments. The cleavage of the 22-kDa/50-kDa junction by elastase increases the Km value for the actin-activated ATPase. The presence of the two protease-sensitive regions in S-1 is consistent with a three-domain structure of the myosin head and may have important implications to the mode of intersite communication in this protein.
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D010450:Endopeptidases / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D009132:Muscles / Q000378:metabolism; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism; D010446:Peptide Fragments / Q000032:analysis / Q000378:metabolism; D011817:Rabbits; D013379:Substrate Specificity
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D010450:Endopeptidases; D009218:Myosins