Structural Stability Effects on the Adsorption and Dodecyltrimethylammonium Bromide-Mediated Elutability of Bacteriophage T4 Lysozyme at Silica Surfaces

Abstract

The effect of structural stability 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 the isoleucine at amino acid position three, yielding a set of proteins with values of Δ G unfolding ranging from 1.2 kcal/mol greater to 2.8 kcal/mol less than that of the wild type. Three structural stability mutants along with the wild type protein were purified from Escherichia coli strains harboring the desired expression vectors. Differences in interfacial behavior among the proteins were observed to be substantial with respect to both the adsorption kinetic behavior and the DTAB-mediated elutability exhibited by each. A positive correlation was observed to exist between elutability and protein stability. A simple mechanism that allows absorbing protein to adopt one of two states, each associated with a different resistance to elution and a different interfacial area occupied per molecule, was used to assist interpretation of the adsorption data recorded prior to surfactant addition. Conditions implicit in the model allowed estimation of the mass of molecules present on the surface just prior to surfactant addition, that were in the more resistant state in each test. The calculated fraction of adsorbed protein in the more tightly bound state correlated positively with resistance to elution.