{Reference Type}: Journal Article
{Title}: Phosphorylation-dependent subcellular redistribution of small myosin light chain kinase.
{Author}: Khapchaev AY;Watterson DM;Shirinsky VP;
{Journal}: Biochim Biophys Acta Mol Cell Res
{Volume}: 1868
{Issue}: 11
{Year}: 10 2021
{Factor}: 5.011
{DOI}: 10.1016/j.bbamcr.2021.119104
{Abstract}: Myosin light chain kinase (MLCK) is a Ca2+-calmodulin-dependent enzyme dedicated to phosphorylate and activate myosin II to provide force for various motile processes. In smooth muscle cells and many other cells, small MLCK (S-MLCK) is a major isoform. S-MLCK is an actomyosin-binding protein firmly attached to contractile machinery in smooth muscle cells. Still, it can leave this location and contribute to other cellular processes. However, molecular mechanisms for switching the S-MLCK subcellular localization have not been described.<BR>Site-directed mutagenesis and in vitro protein phosphorylation were used to study functional roles of discrete in-vivo phosphorylated residues within the S-MLCK actin-binding domain. In vitro co-sedimentation analysis was applied to study the interaction of recombinant S-MLCK actin-binding fragment with filamentous actin. Subcellular distribution of phosphomimicking S-MLCK mutants was studied by fluorescent microscopy and differential cell extraction.<BR>Phosphorylation of S-MLCK actin-binding domain at Ser25 and/or Thr56 by proline-directed protein kinases or phosphomimicking these posttranslational modifications alters S-MLCK binding to actin filaments both in vitro and in cells, and induces S-MLCK subcellular translocation with no effect on the enzyme catalytic properties.<BR>Phosphorylation of the amino terminal actin-binding domain of S-MLCK renders differential subcellular targeting of the enzyme and may, thereby, contribute to a variety of context-dependent responses of S-MLCK to cellular and tissue stimuli.<BR>S-MLCK physiological function can potentially be modulated via phosphorylation of its actin recognition domain, a regulation distinct from the catalytic and calmodulin regulatory domains.