The non–muscle actinopathy–associated mutation E334Q in cytoskeletal γ– actin perturbs interaction of actin filaments with myosin and ADF/cofilin family proteins

Various heterozygous cytoskeletal γ–actin mutations have been shown to cause Baraitser–Winter cerebrofrontofacial syndrome, non–syndromic hearing loss, or isolated eye coloboma. Here, we report the biochemical characterization of human cytoskeletal γ–actin carrying mutation E334Q, a mutation that leads to a hitherto unspecified non–muscle actinopathy. Following expression, purification, and removal of linker and thymosin β4 tag sequences, the p.E334Q monomers show normal integration into linear and branched actin filaments. The mutation does not affect thermal stability, actin filament nucleation, elongation and turnover. Model building and normal mode analysis predict significant differences in the interaction of p.E334Q–filaments with myosin motors and members of the ADF/cofilin family of actin–binding proteins. Assays probing the interactions of p.E334Q–filaments with human class 2 and class 5 myosin motor constructs show significant reductions in sliding velocity and actin–affinity. E334Q differentially affects cofilin-mediated actin dynamics by increasing the rate of cofilin-mediatedde novonucleation of actin filaments and decreasing the efficiency of cofilin-mediated filament severing. Thus, it is likely that p.E334Q-mediated changes in myosin motor activity, as well as filament turnover contribute to the observed disease phenotype.