Myosin I generates movement at the leading edge in cell motility, and class I myosins have been implicated in phagocytosis and vesicle transport. Myosin I, an unconventional myosin, does not form dimers. The catalytic (head) domain has ATPase activity and belongs to the larger group of P-loop NTPases. There are 5 myosin subclasses with subclasses c/h, d/g, and a/b have an IQ domain and a TH1 domain. Myosins are actin-dependent molecular motors that play important roles in muscle contraction, cell motility, and organelle transport. The head domain is a molecular motor, which utilizes ATP hydrolysis to generate directed movement toward the plus end along actin filaments. A cyclical interaction between myosin and actin provides the driving force. Rates of ATP hydrolysis and consequently the speed of movement along actin filaments vary widely, from about 0.04 micrometer per second for myosin I to 4.5 micrometer per second for myosin II in skeletal muscle. Myosin II moves in discrete steps about 5-10 nm long and generates 1-5 piconewtons of force. Upon ATP binding, the myosin head dissociates from an actin filament. ATP hydrolysis causes the head to pivot and associate with a new actin subunit. The release of Pi causes the head to pivot and move the filament (power stroke). Release of ADP completes the cycle. CyMoBase classifications were used to confirm and identify the myosins in this hierarchy.
Feature 1:ATP binding site [chemical binding site]
Evidence:
Structure:1LKX: Dictyostelium discoideum class I myosin, MyoE, bound to MgADP.VO4, contacts at 4A
Comment:composed of the purine-binding loop, the P-loop, Switch-1, and Switch-2
Comment:the residues of the P-loop wrap around the triphosphate region of the nucleotide and the N-terminal region forms the binding pocket for the nucleotide
Jiyao W et al.(2023). "The conserved domain database in 2023.",