Finding the Ph-induced Changes in the Shape of Matrix Viral Protein M1 by Spr Technique

The structure of proteins plays a crucial role in their functioning. We have shown how SPR technique allows to determine the shape of proteins and its changes under influence of external conditions. Adsorption of matrix M1 protein of influenza virus on self-assembled monolayer of mercaptohexadecanoic acid was studied by SPR. Acid groups on substrate surface provide its negative charge similar to the charge of lipid membrane of the influenza virus. The protein adsorbs irreversibly and forms saturated monolayer on the substrate surface. It was shown that the process is governed by electrostatic attraction forces. However, the density of the monolayer depends essentially on the conditions of its formation. It was found that in a neutral medium this protein forms monolayers of identical density at any initial protein concentrations in solution. In an acidic medium (pH below 5) the situation differs. The protein forms more dense layers in concentrated solutions and more rarefied layers in dilute solutions. These results suggest that the protein has rather symmetrical globular shape in a neutral medium, and it becomes an oblong molecule in an acidic medium. In concentrated solutions the elongated protein molecules apparently adsorbs mostly orthogonally to the surface forming a thick coat. In dilute solutions, on the contrary, most of the molecules adsorb laterally, forming thinner layers. This approach can be used to analyze shape of other irreversibly adsorbed proteins and nanoparticles.