Unique sequence of a high molecular weight myosin light chain kinase is involved in interaction with actin cytoskeleton

Myosin light chain kinase (MLCK) is the key regulator of cell motility and smooth muscle contraction in higher vertebrates, We searched for the featur es of the high molecular weight MLCK (MLCK-210) associated with its unique N-terminal sequence not found in a more ubiquitous lower molecular weight M LCK (MLCK-108). MLCK-210 demonstrates stronger association with the Triton- insoluble cytoskeletons than MLCK-108, suggesting the role for this sequenc e in subcellular targeting. Indeed, the expressed unique domain of MLCK-210 binds and bundles F-actin in vitro and colocalises with the microfilaments in transfected cells reproducing endogenous MLCK-210 distribution. Thus, M LCK-210 features an extensive actin binding interface and, perhaps, acts as an actin cytoskeleton stabiliser. (C) 1999 Federation of European Biochemi cal Societies.