Interaction between actin and the effector peptide of MARCKS-related protein - Identification of functional amino acid segments

It is widely assumed that the members of the MARCKS protein family, MARCKS (an acronym for myristoylated alanine-rich C kinase substrate) and MARCKS-r elated protein (MRP), interact with actin via their effector domain, a high ly basic segment composed of 24-25 amino acid residues. To clarify the mech anisms by which this interaction takes place, we have examined the effect o f a peptide corresponding to the effector domain of MRP, the so-called effe ctor peptide, on both the dynamic and the structural properties of actin, W e show that in the absence of cations the effector peptide polymerizes mono meric actin and causes the alignment of the formed filaments into bundle-li ke structures. Moreover, we document that binding of calmodulin or phosphor ylation by protein kinase C both inhibit the actin polymerizing activity of the MRP effector peptide. Finally, several effector peptides were synthesi zed in which positively charged or hydrophobic segments were deleted or rep laced by alanines, Our data suggest that a group of six positively charged amino acid residues at the N-terminus of the peptide is crucial for its int eraction with actin. While its actin polymerizing activity critically depen ds on the presence of all three positively charged segments of the peptide, hydrophobic amino acid residues rather modulate the polymerization velocit y.