MyoX, a MyTH-FERM myosin, is a molecular motor that has crucial functions in the transport and/or tethering of integrins in the actin-based extensions known as filopodia, microtubule binding, and in netrin-mediated axon guidance. It functions as a dimer. MyoX walks on bundles of actin, rather than single filaments, unlike the other unconventional myosins. MyoX is present in organisms ranging from humans to choanoflagellates, but not in Drosophila and Caenorhabditis elegans.MyoX consists of a N-terminal motor/head region, a neck made of 3 IQ motifs, and a tail consisting of a coiled-coil domain, a PEST region, 3 PH domains, a myosin tail homology 4 (MyTH4), and a FERM domain at its very C-terminus. The first PH domain in the MyoX tail is a split-PH domain, interupted by the second PH domain such that PH 1a and PH 1b flanks PH 2. The third PH domain (PH 3) follows the PH 1b domain. This cd contains the third MyoX PH repeat. PLEKHH3/Pleckstrin homology (PH) domain containing, family H (with MyTH4 domain) member 3 is also part of this CD and like MyoX contains a FERM domain, a MyTH4 domain, and a single PH domain. Not much is known about the function of PLEKHH3. PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.
Jiyao W et al.(2023). "The conserved domain database in 2023.",