Structural Stability Effects on Adsorption of Bacteriophage T 4 Lysozyme to Colloidal Silica

approved by: Circular dichroism (CD) spectra were obtained for bacteriophage T4 lysozyme and three of its mutants in the presence and absence of colloidal silica nanoparticles. Mutant lysozymes were produced by substitution of the isoleucine at position 3 with tryptophan, cysteine and leucine. Each substitution resulted in an altered structural stability, quantified by a difference in free energy of unfolding from the wild type. CD spectra recorded in the absence of colloidal silica agreed with x-ray diffraction data in that the mutants and wild type showed similar secondary structures. CD spectra of protein-nanoparticle complexes recorded after contact for 90 minutes showed significant differences from those recorded in the absence of nanoparticles, and these differences varied among the proteins. The percentage of a-helix lost in these proteins upon adsorption to silica nanoparticles was also recorded as a function of time by CD. For a 1:2 protein to particle mixture, different kinetic behaviors were observed among the proteins. The more unstable the protein, thegreater the rate and extent of secondary structure loss upon adsorption. For a 1:1 protein to particle mixture, only results recorded with the tryptophan mutant were significantly different from the other variants. The kinetic data recorded for the 1:2 protein to particle ratiowas evaluated using two different protein adsorption models. Both models allow proteins at an interface to exist in two different states: state 1 molecules retain their native conformation, while state 2 molecules lose a certain amount of their native secondary structure and occupy more surface area than state 1 molecules. The main difference between these two models is that one allows state 2 molecules to be adsorbed directly from solution, while the other Redacted for Privacy requires that state 2 molecules be generated by surface-induced conversion of state 1 molecules. The former model showed a better fit to the data than the latter from a least squares comparison. Both models indicated that proteins of lower thermal stability have a greater tendency to adopt state 2 on silica. Structural Stability Effects on Adsorption of Bacteriophage T4 Lysozyme to Colloidal Silica