Investigation of calmodulin‐like and rod domain mutations suggests common molecular mechanism for α‐actinin‐1‐linked congenital macrothrombocytopenia

Actinin‐1 mutations cause dominantly inherited congenital macrothrombocytopenia (CMTP), with mutations in the actin‐binding domain increasing actinin's affinity for F‐actin. In this study, we examined nine CMTP‐causing mutations in the calmodulin‐like and rod domains of actinin‐1. These mutations increase, to varying degrees, actinin's ability to bundle actin filaments in vitro. Mutations within the calmodulin‐like domain decrease its thermal stability slightly but do not dramatically affect calcium binding, with mutant proteins retaining calcium‐dependent regulation of filament bundling in vitro. The G764S and E769K mutations increase cytoskeletal association of actinin in cells, and all mutant proteins colocalize with F‐actin in cultured HeLa cells. Thus, CMTP‐causing actinin‐1 mutations outside the actin‐binding domain also increase actin association, suggesting a common molecular mechanism underlying actinin‐1 related CMTP. Biochemical analysis of congenital macrothrombocytopenia causing actinin‐1 mutations. Calcium binding not consistently affected by CaM‐like domain mutations. Mutations within the rod and CaM‐like domains increase actinin‐1 association with F‐actin. Similar effect to previously described mutations in the actinin‐1 actin binding domain. Suggests a common molecular mechanism for most disease‐associated actinin‐1 mutations.