Myosin light chain kinase binding to a unique site on F-actin revealed by three-dimensional image reconstruction

• DOI: 10.1083/jcb.200105079
• Publication Date: 2002-07-26T16:46:23Z
• Authors: Victoria Hatch; Gang Zhi; Lula Smith; James T. Stull; Roger Craig; William Lehman
• Keywords: Tropomyosin; Actin-binding protein; Actin remodeling; C-terminus

Ca2+–calmodulin-dependent phosphorylation of myosin regulatory light chains by the catalytic COOH-terminal half chain kinase (MLCK) activates II in smooth and nonmuscle cells. In addition, MLCK binds to thin filaments situ F-actin vitro via a specific repeat motif its NH2 terminus at stoichiometry one per three actin monomers. We have investigated structural basis MLCK–actin interactions negative staining helical reconstruction. was decorated with peptide containing NH2-terminal 147 residues (MLCK-147) that high affinity. MLCK-147 caused formation rafts, single within rafts were used for analysis. Three-dimensional reconstructions showed density on extreme periphery subdomain-1 each monomer forming bridge subdomain-4 azimuthally adjacent actin. Fitting reconstruction atomic model revealed interaction close COOH first near 228–232 second. This unique location enables bind without interfering binding any other key actin-binding proteins, including myosin, tropomyosin, caldesmon, calponin.