THE INFLUENCE OF NET CHARGE AND CHARGE LOCATION ON THE ADSORPTION ANDDODECYLTRIMETHYLAMMONIUM BROMIDE-MEDIATED ELUTABILITY OF BACTERIOPHAGE-T4 LYSOZYME AT SILICA SURFACES

The effect of net charge and charge location on the adsorption and dod ecyltrimethylammonium bromide (DTAB)-mediated elutability of bacteriop hage T4 lysozyme was monitored at hydrophilic and hydrophobic silica s urfaces with in situ ellipsometry. Mutant lysozymes were produced by s ubstitution of selected lysine residues with glutamic acid, each subst itution thus decreasing the net charge of the protein by 2 units. The wildtype protein (net charge +9) and four mutant proteins, each of net charge +7 or +5, were purified from Escherichia coli strains harborin g the desired expression vectors. Differences in interfacial behavior among the proteins were observed with respect to both the adsorption k inetics and the DTAB-mediated elutability exhibited by each. No simple relationship between protein net charge and surface behavior was obse rved, indicating that the location of the charge replacements had the major effect on surface behavior. At hydrophilic surfaces, mutations a llowing the most mobile regions of positive charge to more readily ori ent toward the interface increased that protein's resistance to elutab ility; at hydrophobic surfaces, mutations favoring or otherwise not in hibiting hydrophobic association between the protein and the surface i ncreased the resistance to elutability. This was not related to protei n net charge, but to the probable influence of the location of each su bstitution relative to the other mobile, solvent-exposed, charged side chains of the molecule. (C) 1995 Academic Press, Inc.