Kinetic Characterization of Nonmuscle Myosin IIB at the Single Molecule Level

Abstract

Background: Nonmuscle myosin IIB (NMIIB) is a key player in cell motility. Results: Although the individual NMIIB molecules are not processive, NMIIB thick filaments show robust processive motion. Conclusion: NMIIB forms processive thick filament in vitro, which is likely the functional unit in cells. Significance: We demonstrate how processive systems can be formed from nonprocessive individual molecules.

Magnesium Modulates Actin Binding and ADP Release in Myosin Motors

“…In MV, NMIIA, CMIIB, and SMII, the calculated detachment rates are within 2-3-fold of the measured ADP release rate constants (Table 4). Differences between the calculated and measured detachment rates have been noted previously (51) and could result from a number of factors, including strain dependence of detachment or uncertainty in the working stroke values.…”

“…Overall, Mg 2ϩ dependence of in vitro sliding velocity can mostly be explained by a detachment-limited mechanism of motility. The detachment rate (1/t on ) at low and high Mg 2ϩ can be calculated using the in vitro sliding velocities (V) and the literature values of the working stroke (d uni ) (MV (48); SKII (49), SMII (50), NMII (51), and CMIIB (52)). In MV, NMIIA, CMIIB, and SMII, the calculated detachment rates are within 2-3-fold of the measured ADP release rate constants (Table 4).…”

Myosin-10 produces its power-stroke in two phases and moves processively along a single actin filament under low load

“…(C) ATP dependence of detachment rate, determined from event lifetime histograms measured at different ATP concentrations, exhibited Michaelis-Menten type kinetics with V max = 14.0 ± 0. event, the bead displacement from its mean rest position was measured to determine the average power stroke amplitude (see below), and event duration was measured to estimate the average attached lifetimes and hence detachment rate as a function of ATP concentration (100 nM to 400 μM ATP). Attached lifetime histograms were fitted to a single exponential process (39,40) (Fig. 3B and SI Text), and the rate constants were plotted against the ATP concentration ( Fig.…”

Mammalian Myosin-18A, a Highly Divergent Myosin

“…This is consistent with the optical trapping results showing transient interactions with actin in a nucleotide-independent manner that do not result in a net displacement of the actin filament. Interestingly, unphosphorylated nonmuscle myosin 2B HMM also gave a 0-nm displacement when interacting with actin in the optical trap (41). The weak F-actin affinity of myosin-18A could still be physiologically significant because this myosin is localized in the lamellipodia of some cells (11,42) where the actin concentration is in the range of 500 M (43).…”