The sequence of the myosin 50-20K loop affects Myosin's affinity for actin throughout the actin-myosin ATPase cycle and its maximum ATPase activity.

TitleThe sequence of the myosin 50-20K loop affects Myosin's affinity for actin throughout the actin-myosin ATPase cycle and its maximum ATPase activity.
Publication TypeJournal Article
Year of Publication1999
AuthorsMurphy CT, Spudich JA
JournalBiochemistry
Volume38
Issue12
Pagination3785-92
Date Published1999 Mar 23
ISSN0006-2960
KeywordsActins, Adenosine Triphosphatases, Adenosine Triphosphate, Animals, Dictyostelium, Electrochemistry, Myosins, Nucleotides, Protein Conformation
Abstract

We are interested in the role that solvent-exposed, proteolytically sensitive surface loops play in myosin function. The 25-50K loop, or loop 1, is near the ATP binding site, while the 50-20K loop (loop 2) is in the actin binding site. Through chimeric studies, we have found that loop 1 affects ADP release [Murphy, C. T., and Spudich, J. A. (1998) Biochemistry 37, 6738-44], while loop 2 affects the actin-activated ATPase activity [Uyeda, T. Q.-P., et al. (1994) Nature 368, 567-9]. In the study described here, we have found that the kcat of the actin-activated ATPase activity is changed by the loop 2 substitutions in a manner that reflects the relative actin-activated ATPase activities of the donor myosins. Additionally, changes in loop 2 affect the affinity of myosin for actin both in the presence and in the absence of nucleotides. Pre-steady-state studies together with the ATPase and affinity data suggest that while loop 2 does not affect interactions between myosin and nucleotide, it plays a role in determining the affinity of myosin for actin in various nucleotide states and in the rate-limiting transition allowing phosphate release.

DOI10.1021/bi9826815
Alternate JournalBiochemistry
PubMed ID10090768
Grant ListAR42895 / AR / NIAMS NIH HHS / United States