Myosin light chain kinase binding to actin filaments

Smooth muscle myosin light chain kinase (MLCK) plays important roles in con tractile-motile processes of a variety of cells. Three DFRxxL motifs at the kinase N-terminus (residues 2-63) are critical for high-affinity binding t o actin-containing filaments [Smith et al. (1999) J. Biol. Chem. 274, 29433 -29438]. A GST fusion protein containing residues 1-75 of MLCK (GST75-MLCK) bound maximally to both smooth muscle myofilaments and F-actin at 0.28 and 0.31 mol GST75-MLCK/mol actin,vith respective K-D values of 0.1 mu M and 0 .8 mu M. High-affinity binding of MLCK to actin-containing filaments may be due to each DFRxxL motif binding to one actin monomer in filaments. (C) 20 00 Federation of European Biochemical Societies. Published by Elsevier Scie nce B.V. All rights reserved.