Regulation of the binding of myristoylated alanine-rich C kinase substrate(MARCKS) related protein to lipid bilayer membranes by calmodulin

The effector domain (ED) of MARCKS proteins can associate with calmodulin ( CaM) as well as with phospholipids, It is not clear, however, whether a com plex between MARCKS proteins and CaM can form at the surface of phospholipi d membranes or whether CaM and membranes compete for ED binding. Using two- mode waveguide spectroscopy, we have investigated how CaM regulates the ass ociation of MARCKS-related protein (MRP) with planar supported phospho lipi d bilayer membranes. Bringing a solution containing CaM into contact with m embranes on which MRP had previously been deposited results in low-affinity binding of CaM to MRP. A preformed, high-affinity CaM . MRP complex in the aqueous phase binds much more slowly than pure MRP to membranes. Similar o bservations were made when a peptide corresponding to the ED of MRP was use d instead of MRP. Hence CaM cannot form a stable complex with MRP once the latter is bound at the membrane surface, CaM can, however, strongly retard the association of MRP with lipid membranes. The most likely interpretation of these results is that CaM and the phospholipid membrane share the same binding region at the ED and that the ED is forced by membrane binding to a dopt a conformation unfavorable for CaM binding. (C) 2000 Academic Press.