TY - JOUR
T1 - 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
AU - Murphy, Coleen T.
AU - Spudich, James A.
PY - 1999/3/23
Y1 - 1999/3/23
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=0033596962&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0033596962&partnerID=8YFLogxK
U2 - 10.1021/bi9826815
DO - 10.1021/bi9826815
M3 - Article
C2 - 10090768
AN - SCOPUS:0033596962
SN - 0006-2960
VL - 38
SP - 3785
EP - 3792
JO - Biochemistry
JF - Biochemistry
IS - 12
ER -