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

Biochemistry. 1999 Mar 23;38(12):3785-92. doi: 10.1021/bi9826815.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actins / metabolism*
  • Adenosine Triphosphatases / metabolism*
  • Adenosine Triphosphate / metabolism*
  • Animals
  • Dictyostelium / metabolism
  • Electrochemistry
  • Myosins / chemistry
  • Myosins / metabolism*
  • Nucleotides / metabolism
  • Protein Conformation


  • Actins
  • Nucleotides
  • Adenosine Triphosphate
  • Adenosine Triphosphatases
  • Myosins