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

Coleen T. Murphy, James A. Spudich

Research output: Contribution to journalArticlepeer-review

73 Scopus citations

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 k(cat) 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.

Original languageEnglish (US)
Pages (from-to)3785-3792
Number of pages8
JournalBiochemistry
Volume38
Issue number12
DOIs
StatePublished - Mar 23 1999
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biochemistry

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