Glucagon adsorption on polymer surfaces with alpha-helical and extended beta-strand conformations: a computational...

The adsorption of glucagon with alpha-helical and extended beta-strand conformations on polymer surfaces was investigated using a computer simulation approach. An X-ray crystallographic structure of glucagon was employed in the study of the alpha-helical glucagon adsorption. The X-ray structure was then modified to simulate an extended beta-strand structure in the study of the beta-strand glucagon adsorption. Totally, 1632 different adsorption orientations of glucagon with each conformation were examined on polystyrene, polypropylene, polyethylene, poly(hydroxyethyl methacrylate) and poly(vinyl alcohol) surfaces. The calculation of the average adsorption energies among different orientations did not reveal any marked difference between the two conformations. However, when the lowest-energy orientations were compared, the adsorption energy of the extended beta-strand glucagon was always much lower than that of the alpha-helical glucagon, indicating that the adsorption of extended beta-strand glucagon was more energy favorable. The lower adsorption energy for the extended beta-strand glucagon than for the alpha-helical glucagon appeared to be contributed by the lower interaction potential energy of the former conformation. A greater number of the surface atoms in the extended beta-strand glucagon than in the alpha-helical glucagon was also observed. Fourier transform infrared spectroscopic (FTIR) studies in the literature showed conformational changes in adsorption of various larger proteins. Our study appears to provide a theoretical insight for the results from the FTIR studies.