Key Concepts of Section 17.5

• Myosins are actin-based motors powered by ATP hydrolysis.

• Myosins have a motor head domain, a lever-arm neck domain, and a cargo-binding tail domain (see Figure 17-22).

• There are many classes of myosins, three of which are present in many eukaryotes: myosin I, which has a single head domain; myosin II, which has two heads and assembles into bipolar filaments; and myosin V, which has two heads but does not assemble into filaments (see Figure 17-25).

• Myosins convert ATP hydrolysis to mechanical work by amplifying a small conformational change in the head through the neck domain when the head is bound to F-actin (see Figure 17-26).

• Myosin heads take discrete steps along an actin filament, which can be small (8 nm) and nonprocessive in the case of myosin II, or large (36 nm for the motor overall, 72 nm for each head) and processive for myosin V.