The Influence of Net Charge and Charge Location on the Adsorption and Dodecyltrimethylammonium Bromide-Mediated Elutability of Bacteriophage T4 Lysozyme at Silica Surfaces

Abstract

The effect of net charge and charge location on the adsorption and dodecyltrimethylammonium bromide (DTAB)-mediated elutability of bacteriophage T4 lysozyme was monitored at hydrophilic and hydrophobic silica surfaces with in situ ellipsometry. Mutant lysozymes were produced by substitution of selected lysine residues with glutamic acid, each substitution thus decreasing the net charge of the protein by 2 units. The wild-type protein (net charge +9) and four mutant proteins, each of net charge +7 or +5, were purified from Escherichia coli strains harboring the desired expression vectors. Differences in interfacial behavior among the proteins were observed with respect to both the adsorption kinetics and the DTAB-mediated elutability exhibited by each. No simple relationship between protein net charge and surface behavior was observed, indicating that the location of the charge replacements had the major effect on surface behavior. At hydrophilic surfaces, mutations allowing the most mobile regions of positive charge to more readily orient toward the interface increased that protein's resistance to elutability; at hydrophobic surfaces, mutations favoring or otherwise not inhibiting hydrophobic association between the protein and the surface increased the resistance to elutability. This was not related to protein net charge, but to the probable influence of the location of each substitution relative to the other mobile, solvent-exposed, charged side chains of the molecule.