EFFECT OF STRUCTURAL STABILITY ON THE CHARACTERISTICS OF ADSORBED LAYERS OF T4 LYSOZYME

The interferometric surface force technique has been employed to deter mine how the structural stability of globular proteins affects their a dsorption and the interactions between adsorbed protein layers. The sy stem consisted of positively charged bacteriophage T4 lysozyme and neg atively charged mica surfaces. The wild type and one synthetic mutant of the protein, Ile3 --> Trp, differing in structural stability while the total charge and tertiary structure are the same, were studied. Th e adsorption leads to a nearly complete neutralization of the negative surface charge of mica, reducing the long-range electrostatic double- layer interaction acting between mica surfaces. The thickness of the a dsorbed layer is for the wild type consistent with the dimensions of t he protein, while the Ile3 --> Trp mutant gives a layer with a thickne ss smaller than any of its native dimensions. Another consequence of t he difference in structural stability is that the short range attracti on between one protein layer and one bare mica surface is an order of magnitude larger for the Ile3 --> Trp mutant than for the wild type. T he results demonstrate that the less stable mutant loses its tertiary structure upon adsorption, whereas the wild type retains its globular shape. These differences provide an understanding for the differences in adsorbed amount and complements the information about changes in se condary structure upon adsorption observed with other methods.