Myosin motor domain of muscle myosin heavy chain 18. Class II myosins, also called conventional myosins, are the myosin type responsible for producing actomyosin contraction in metazoan muscle and non-muscle cells. Myosin II contains two heavy chains made up of the head (N-terminal) and tail (C-terminal) domains with a coiled-coil morphology that holds the two heavy chains together. The intermediate neck domain is the region creating the angle between the head and tail. It also contains 4 light chains which bind the heavy chains in the "neck" region between the head and tail. The head domain is a molecular motor, which utilizes ATP hydrolysis to generate directed movement toward the plus end along actin filaments. Class-II myosins are regulated by phosphorylation of the myosin light chain or by binding of Ca2+. A cyclical interaction between myosin and actin provides the driving 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.