Myosin-XVIIIa (MYO18A) is a unique PDZ domain-containing unconventional myosin conserved from Drosophila to vertebrates. Unlike conventional myosins, it has weak ATP-insensitive actin binding ability and does not act as actively translocating motor [, ]. Golgi protein GOLPH3 binds to MYO18A, and this interaction has been suggested to provide the link between Golgi and F-actin []. MYO18A may also function in the adhesion process that maintains the stable attachment of myofibres to ECM (extracellular matrix) and muscle integrity during early development [].
Many members of myosin class XVIII contain an N-terminal PDZ domain which is commonly found in proteins establishing molecular complexes. Mammals express a second isoform, Myo18B, that lacks the PDZ domain []. They also contain a motor domain which does not exhibit ATPase activity, suggesting that these myosins function as an actin tether protein [, ]. They also have two IQ domains that probably bind light chains or related calmodulins and a C-terminal tail with two sections of coiled-coil domains, which are thought to mediate homodimerization []. Myo18A has been implicated in stromal cell differentiation []and Myo18B in tumor suppression [].This entry represents the motor domain.
