title: Myosin heavy-chain kinase A from Dictyostelium possesses a novel actin-binding domain that cross-links actin filaments.
abstract: Myosin heavy-chain kinase A (MHCK A) catalyses the disassembly of myosin II filaments in Dictyostelium cells via myosin II heavy-chain phosphorylation. MHCK A possesses a 'coiled-coil'-enriched domain that mediates the oligomerization, cellular localization and actin-binding activities of the kinase. F-actin (filamentous actin) binding by the coiled-coil domain leads to a 40-fold increase in MHCK A activity. In the present study we examined the actin-binding characteristics of the coiled-coil domain as a means of identifying mechanisms by which MHCK A-mediated disassembly of myosin II filaments can be regulated in the cell. Co-sedimentation assays revealed that the coiled-coil domain of MHCK A binds co-operatively to F-actin with an apparent K(D) of approx. 0.5 muM and a stoichiometry of approx. 5:1 [actin/C(1-498)]. Further analyses indicate that the coiled-coil domain binds along the length of the actin filament and possesses at least two actin-binding regions. Quite surprisingly, we found that the coiled-coil domain cross-links actin filaments into bundles, indicating that MHCK A can affect the cytoskeleton in two important ways: (1) by driving myosin II-filament disassembly via myosin II heavy-chain phosphorylation, and (2) by cross-linking/bundling actin filaments. This discovery, along with other supporting data, suggests a model in which MHCK A-mediated bundling of actin filaments plays a central role in the recruitment and activation of the kinase at specific sites in the cell. Ultimately this provides a means for achieving the robust and highly localized disruption of myosin II filaments that facilitates polarized changes in cell shape during processes such as chemotaxis, cytokinesis and multicellular development.
authors.affiliation: Department of Biology, University of North Carolina at Greensboro, Greensboro, NC 27402, USA.
authors.forename: Misty
authors.initials: M
authors.lastname: Russ
authors.forename: Daniel
authors.initials: D
authors.lastname: Croft
authors.forename: Omar
authors.initials: O
authors.lastname: Ali
authors.forename: Raquel
authors.initials: R
authors.lastname: Martinez
authors.forename: Paul A
authors.initials: PA
authors.lastname: Steimle
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry* / Q000378:metabolism*; D004023:Dictyostelium / Q000201:enzymology*; D008840:Microfilament Proteins / Q000378:metabolism*; D010449:Peptide Mapping; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D015800:Protozoan Proteins; D014335:Tropomyosin / Q000378:metabolism
chemical_list: D000199:Actins; D008840:Microfilament Proteins; D015800:Protozoan Proteins; D014335:Tropomyosin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C033142:myosin-heavy-chain kinase