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class VI myosin, motor domain Myosin VI is a monomeric myosin, which moves towards the minus-end of actin filaments, in contrast to most other myosins which moves towards the plus-end of actin filaments. It is thought that myosin VI, unlike plus-end directed myosins, does not use a pure lever arm mechanism, but instead steps with a mechanism analogous to the kinesin neck-linker uncoupling model. It has been implicated in a myriad of functions including: the transport of cytoplasmic organelles, maintenance of normal Golgi morphology, endocytosis, secretion, cell migration, border cell migration during development, and in cancer metastasis playing roles in deafness and retinal development among others. While how this is accomplished is largely unknown there are several interacting proteins that have been identified such as disabled homolog 2 (DAB2), GIPC1, synapse-associated protein 97 (SAP97; also known as DLG1) and optineurin, which have been found to target myosin VI to different cellular compartments. The catalytic (head) domain has ATPase activity and belongs to the larger group of P-loop NTPases. 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 minus 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. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",