Subtilisin cleavage of actin decreased its polymerization rate, increased critical concentration, and reduced its affinity for myosin subfragment 1 by about 10-fold compared to intact actin.
Subtilisin cleavage of actin between Met-47 and Gly-48 alters its polymerization kinetics and macromolecular interactions, providing insights into actin structure-function relationships.
Homogeneous preparations of actin cleaved into two fragments, the N-terminal 9- and C-terminal 36-kDa peptides, were achieved by proteolysis of G-actin with subtilisin at 23 degrees C at a 1:1000 (w/w) ratio of enzyme to actin. The subtilisin cleavage site was identified by sequence analysis to be between Met-47 and Gly-48. Although under nondenaturing conditions the two fragments remained associated to one another, the cleavage affected macromolecular interactions of actin. The rates of cleaved actin polymerization by MgCl2, KCl, and myosin subfragment 1 (S-1) were slower and the critical concentrations for this process were higher than in intact protein. Intact and cleaved actin formed morphologically indistinguishable filaments and copolymerized in the presence of MgCl2. The affinity of actin for S-1 was decreased by about 10-fold due to subtilisin cleavage, but the S-1 ATPase activity was activated to the same Vmax value by both intact and cleaved actins. DNase I inhibition measurements revealed lower affinity of cleaved actin for DNase I than that of intact protein. These results are discussed in terms of actin's structure.
Schwyter et al. (1989) studied this question. Subtilisin cleavage of actin vs. Intact actin was evaluated on Polymerization rates, critical concentrations, and affinity for myosin subfragment 1 (S-1). Subtilisin cleavage of actin decreased its polymerization rate, increased critical concentration, and reduced its affinity for myosin subfragment 1 by about 10-fold compared to intact actin.