Alpha-kinase domain of myosin heavy chain kinase and similar domains
This group is composed of alpha-kinase domains of Dictyostelium discoideum myosin heavy chain kinases A-D (MHCKA, MHCKB, MHCKC, MHCKD), alpha-protein kinase 1 (AK1), and similar proteins. The myosin heavy chain kinases are involved in regulating myosin II filament assembly in Dictyostelium discoideum. They phosphorylate target threonine residues located in the carboxyl-terminal portion of the myosin II heavy chain (MHC) tail, resulting in filament disassembly. The different MHCK isoforms display different spatial regulation, indicating specific roles for each isoform in fine tuning the Dictyostelium actomyosin cytoskeleton. They all contain an alpha-kinase domain as well as WD40 repeats at the C-terminus. AK1 contains an N-terminal Arf-GAP domain and a central alpha-kinase domain. Alpha-kinase is an atypical protein kinase catalytic domain with no detectable similarity to conventional protein serine/threonine kinases. The alpha-kinase family was named after the unique mode of substrate recognition by its initial members, the Dictyostelium heavy chain kinases, which targeted protein sequences that adopt an alpha-helical conformation. More recently, alpha-kinases were found to also target residues in non-helical regions.
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