Myosin X, also known as MYO10, is a protein that in humans is encoded by the MYO10 gene. Myo10 is an actin-based motor protein that can localize to the tips of the finger-like cellular protrusions known as filopodia. Myo10 is broadly expressed in mammalian tissues, although at relatively low levels. Studies with knockout mice demonstrate that Myo10 has important functions in embryonic processes such as neural tube closure and eye development. Myo10 also has important functions in cancer invasion and growth. Myo10 should not be confused with Myh10, which encodes the heavy chain of the class II myosin known as non-muscle myosin 2b. Structure and function The human MYO10 gene spans ~274 kb and is located on chromosome 5 band 5p15.1 (GRCh Ensembl release 89). It produces a full-length RNA transcript with 41 exons encoding a MYO10 heavy chain whose deduced sequence has 2058 amino acids and a predicted molecular weight of ~237 kDa. Like many motor proteins, the full-length Myo10 protein can be considered to consist of a head, neck, and tail. The N-terminal head or myosin motor domain can bind to an actin filament, hydrolyze ATP, and produce force. The neck or light chain binding domain consists of 3 IQ motifs, with each IQ motif providing a binding site for one molecule of calmodulin, a ~16.5 kDa calcium-binding protein. Unlike most calmodulin binding sites, which only bind to calmodulin in the presence of calcium, the IQ motifs in Myo10 can bind to calmodulin in the absence of calcium. The Myo10 IQ motifs have also been reported to bind CALML3, a calmodulin-like protein expressed in epithelial cells, so CALML3 may serve as a Myo10 light chain in place of calmodulin in some situations. The Myo10 tail begins with an alpha-helical region whose proximal portion forms a single, stable alpha helix (SAH domain) that lengthens the lever arm formed by the neck domain. The distal portion of the alpha helical region can self-associate with a Kd of ~0.6 uM to form an antiparallel coiled coil, allowing two Myo10 heavy chains to form an antiparallel dimer, a unique structure among known myosins. The Myo10 tail includes several regions in addition to the SAH and coiled coil. These include a region with 3 PEST sequences—sequences enriched in the amino acids Proline (P), Glutamine (E), Serine (S), and T (Threonine) that are often associated with cleavage by proteases such as calpain. The Myo10