Myosin heavy chain kinase B participates in the regulation of myosin assembly into the cytoskeleton

Myosin II plays critical roles in events such as cytokinesis, chemotactic migration, and morphological changes during multicellular development. The amoeba Dictyostelium discoideum provides a simple system for the study of this contractile protein. In this system, myosin II filament assembly is regulated by myosin heavy chain (MHC) phosphorylation in the tail region of the molecule. Earlier studies identified an alpha-kinase, MHC kinase A (MHCK A), which phosphorylates three mapped threonine residues in the myosin tail, driving myosin disassembly. Using molecular and genomic approaches, we have identified a series of related kinases in Dictyostelium. The enzyme MHCK B shares with MHCK A a domain organization that includes a highly novel catalytic domain coupled to a carboxyl-terminal WD repeat domain. We have engineered, expressed, and purified a FLAG-tagged version of the novel kinase. In the present study, we report detailed biochemical and cellular studies documenting that MHCK B plays a physiological role in the control of Dictyostelium myosin II assembly and disassembly during the vegetative life of Dictyostelium amoebae. The presented data supports a model of multiple related MHCKs in this system, with different regulatory mechanisms and pathways controlling each enzyme.