Unconventional myosin-IXa (MYO9A) belongs to class IX myosin that contains an extra Rho-specific GAP (GTPase-activating protein) domain in the tail region []. In mice, MYO9A homologue, Myr7 regulates Rho by stimulating it's GTPase activity in neurons and has a role in the regulation of neuronal morphology and function []. In humans, there are two proteins in class IX, MYO9A and MYO9B. Class IX myosins may carry its own Rho-GAP tail using its motor head domain to sites that require down-regulation of Rho-dependent signalling [].Myosin constitutes a large superfamily of actin-dependent molecular motors. Myosin binds to actins and moves along actin filaments by using the energy from ATP hydrolysis. Myosin is involved in muscular contraction, cytokinesis, membrane trafficking and signal transduction [, ]. Myosins are typically composed of three functional domains:Motor head domain whose core sequence is highly conserved in all the myosin classes. This domain binds to actin and uses ATP hydrolysis to generate force to move along actin filaments. Neck domain composed of a long helix of variable length depending on the number of IQ motifs (has a consensus sequence of IQXXXRGXXXR) []. This domain acts as a linker and as a lever arm. The neck domain also serves as a binding site for moysin light chains, which are calmodulin-like proteins that have regulatory functions. Tail domain is the most diverse domain and vary in length and in sequence. Many myosin tails form coiled-coil structure that allow the molecules to dimerise and produce two-headed molecules. This domain mediates interaction with cargo molecules and/or other myosin subunits.
Unconventional myosin-IXb (MYO9B) belongs to class IX myosin that contains an extra Rho-specific GAP (GTPase-activating protein) domain in the tail region []. MYO9B plays an important part in spatially coordinated cell shape changes and motility []. In humans, there are two proteins in class IX, MYO9A and MYO9B. Class IX myosins may carry its own Rho-GAP tail using its motor head domain to sites that require down-regulation of Rho-dependent signalling [].Myosin constitutes a large superfamily of actin-dependent molecular motors. Myosin binds to actins and moves along actin filaments by using the energy from ATP hydrolysis. Myosin is involved in muscular contraction, cytokinesis, membrane trafficking and signal transduction [, ]. Myosins are typically composed of three functional domains:Motor head domain whose core sequence is highly conserved in all the myosin classes. This domain binds to actin and uses ATP hydrolysis to generate force to move along actin filaments. Neck domain composed of a long helix of variable length depending on the number of IQ motifs (has a consensus sequence of IQXXXRGXXXR) []. This domain acts as a linker and as a lever arm. The neck domain also serves as a binding site for moysin light chains, which are calmodulin-like proteins that have regulatory functions. Tail domain is the most diverse domain and vary in length and in sequence. Many myosin tails form coiled-coil structure that allow the molecules to dimerise and produce two-headed molecules. This domain mediates interaction with cargo molecules and/or other myosin subunits.
