MARCKS-related protein binds to actin without significantly affecting actin polymerization or network structure

Actin is a 42-kDa protein which, due to its ability to polymerize into fila ments (F-actin), is one of the major constituents of the cytoskeleton. It h as been proposed that MARCKS (an acronym for myristoylated alanine-rich C k inase substrate) proteins play an important role in regulating the structur e and mechanical properties of the actin cytoskeleton by cross-linking acti n filaments. We have recently reported that peptides corresponding to the e ffector domain of MARCKS proteins promote actin polymerization and cause ma ssive bundling of actin filaments. We now investigate the effect of MARCKS- related protein, a 20-kDa member of the MARCKS family, on both filament str ucture and the kinetics of actin polymerization in vitro. Our experiments d ocument that MRP binds to F-actin with micromolar affinity and that the myr istoyl chain at the N-terminus of MRP is not required for this interaction. In marked contrast to the effector peptide, binding of MRP is not accompan ied by an acceleration of actin polymerization kinetics, and we also could not reliably observe an. actin cross-linking activity of MRP. (C) 2000 Acad emic Press.