Identification of a new mechanism for targeting myosin II heavy chain phosphorylation by <it>Dictyostelium </it>myosin heavy chain kinase B

• Main Authors: Steimle Paul A, Greene Jonathan, Underwood Julie
• Format: Article
• Language: English
• Published: BMC 2010-03-01
• Series: BMC Research Notes
• Online Access: http://www.biomedcentral.com/1756-0500/3/56

<p>Abstract</p> <p>Background</p> <p>Heavy chain phosphorylation plays a central role in regulating myosin II bipolar filament assembly in <it>Dictyostelium</it>, as well as in higher eukaryotic nonmuscle cells. Our previous work has demonstrated that the WD-repeat domain of <it>Dictyostelium </it>myosin II heavy chain kinase B (MHCK-B), unlike its counterpart in MHCK-A, is not absolutely required for targeting of the kinase to phosphorylate MHC. Thus, we tested the hypothesis that an asparagine-rich and structurally disordered region that is unique to MHCK-B can by itself function in substrate targeting.</p> <p>Findings</p> <p>Biochemical assays comparing the activities of full-length MHCK-B, a truncation lacking only the WD-repeat domain (B-Δ-WD), and a truncation lacking both the N-rich region and the WD-repeat domain (B-Δ-N-WD) revealed that the N-rich region targets MHCK-B to phosphorylate MHC in a manner that leads to bipolar filament disassembly. This targeting is physiologically relevant since cellular over-expression of the B-Δ-WD truncation, but not the B-Δ-N-WD truncation, leads to dramatically reduced levels of myosin II filament assembly and associated defects in cytokinesis and multicellular development.</p> <p>Conclusions</p> <p>The results presented here demonstrate that an intrinsically unstructured, and asparagine-rich, region of a MHCK-B can mediate specific targeting of the kinase to phosphorylate myosin II heavy chain. This targeting involves a direct binding interaction with myosin II filaments. In terms of regulating myosin bipolar filament assembly, our results suggest that factors affecting the activity of this unique region of MHCK-B could allow for regulation of MHCK-B in a manner that is distinct from the other MHCKs in <it>Dictyostelium</it>.</p>