STRUCTURAL STABILITY EFFECTS ON THE ADSORPTION AND DODECYLTRIMETHYLAMMONIUM BROMIDE-MEDIATED ELUTABILITY OF BACTERIOPHAGE-T4 LYSOZYME AT SILICA SURFACES

The effect of structural stability on the adsorption and dodecyltrimet hylammonium bromide (DTAB)-mediated elutability of bacteriophage T4 ly sozyme was monitored at hydrophilic and hydrophobic silica surfaces wi th in situ ellipsometry. Mutant lysozymes were produced by substitutio n of the isoleucine at amino acid position three, yielding a set of pr oteins with values of Delta G(unfolding) ranging from 1.2 kcal/mol gre ater 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 coil strains harboring the desired expression vectors. Di fferences in interfacial behavior among the proteins were observed to be substantial with respect to both the adsorption kinetic behavior an d the DTAB-mediated elutability exhibited by each. A positive correlat ion was observed to exist between elutability and protein stability. A simple mechanism that allows absorbing protein to adopt one of two st ates, each associated with a different resistance to elution and a dif ferent interfacial area occupied per molecule, was used to assist inte rpretation of the adsorption data recorded prior to surfactant additio n. Conditions implicit in the model allowed estimation of the mass of molecules present on the surface just prior to surfactant addition, th at were in the more resistant state in each test. The calculated fract ion of adsorbed protein in the more tightly bound state correlated pos itively with resistance to elution. (C) 1995 Academic Press, Inc.