Nonelectrostatic contributions to the binding of MARCKS-related protein tolipid bilayers

The association of various protein constructs of MARCKS-related protein (MR P) lacking the myristoyl moiety or the basic effector domain (ED) or both t o neutral and acidic supported planar phospholipid bilayer membranes has be en monitored using two-mode optical waveguide spectroscopy. The importance of the myristoyl moiety for interaction with both neutral and acidic membra nes is demonstrated but unmyristoylated MRP still binds appreciably to neut ral membranes, albeit less than to acidic membranes. Only when both the myr istoyl moiety and the ED are excised does the interaction fall to zero in t he case of the acidic membranes, with very small residual binding still det ectable in the presence of neutral membranes. These results point to the im portance of hydrophobic interactions apart from those associated with the m yristoyl moiety in the association of MRP with membranes. The ED is well en dowed with hydrophobic as well as with basic residues, and the former are c hiefly responsible for binding unmyristoylated MRP to neutral membranes: Th e very small residual attraction between MRP lacking both the myristoyl moi ety and the ED is completely outweighed by electrostatic repulsion between the net acidic MRP and the acidic lipid head groups. (C) 1999 Academic Pres s.