Mutations in Human Nonmuscle Myosin IIA Found in Patients with May-Hegglin Anomaly and Fechtner Syndrome Result in Impaired Enzymatic Function

Abstract

A family of autosomal-dominant diseases including May-Hegglin anomaly, Fechtner syndrome, Sebastian syndrome, Alport syndrome, and Epstein syndrome are commonly characterized by giant platelets and thrombocytopenia. In addition, there may be leukocyte inclusions, deafness, cataracts, and nephritis, depending on the syndrome. Mutations in the human nonmuscle myosin IIA heavy chain gene (MYH9) have been linked to these diseases. Two of the recently described mutations, N93K and R702C, are conserved in smooth and nonmuscle myosins from vertebrates and lie in the head domain of myosin. Interestingly, the two mutations lie within close proximity in the three-dimensional structure of myosin. These two mutations were engineered into a heavy meromyosin-like recombinant fragment of nonmuscle myosin IIA, which was expressed in baculovirus along with the appropriate light chains. The R702C mutant displays 25% of the maximal MgATPase activity of wild type heavy meromyosin and moves actin filaments at half the wild type rate. The effects of the N93K mutation are more dramatic. This heavy meromyosin has only 4% of the maximal MgATPase activity of wild type and does not translocate actin filaments in an in vitro motility assay. Biochemical characterization of the mutant is consistent with this mutant being unable to fully adopt the "on" conformation.

An actin–myosin-II interaction is involved in maintaining the contractile ring in fission yeast

“…The R702C and R709C mutants of human non-muscle myosin IIA and myosin IIB show ∼20% of the maximum actinactivated ATPase activity of wt and have a higher affinity for actin in the presence of ATP (its K m value is less than one-third that of wt) owing to the very slow release of ADP (Kim et al, 2005). Moreover, the motilities of the mutant myosins are severely impaired (Hu et al, 2002;Kim et al, 2005). The local concentration of the corresponding Myo3-R694C mutant in the ring was 1.8-fold higher than that of wt (Fig.…”

Nonmuscle Myosin II Is Required for Internalization of the Epidermal Growth Factor Receptor and Modulation of Downstream Signaling

“…These mutant NM IIs are impaired in their enzymatic activity and ability to translocate actin filaments in an in vitro motility assay, although both mutants can bind to actin and are released by ATP (41,42). Furthermore, these mutations have been shown to cause defects in humans (43) and in mice (44).…”

The May-Hegglin anomaly gene MYH9 is a negative regulator of platelet biogenesis modulated by the Rho-ROCK pathway

“…20 As an abundant motor protein within MKs and the only representative of its family, 21 myosin-IIA is a good candidate mediator of proplatelet extension or platelet release. Biochemical studies suggest that certain N-terminal mutations found in patients with MYH9-related disorders reduce intrinsic ATPase activity, 22 whereas other common C-terminal mutations may compromise myosin filament formation. 23 Although both classes of mutations may interfere with myosin-IIA function, it is unclear whether monoallelic MYH9 mutations produce clinical phenotypes as a result of haploinsufficiency or dominant-negative effects.…”