title: Conformational transitions of adsorbed proteins on surfaces of varying polarity.
abstract: Combining a wide range of protein adsorption experiments (three globular proteins on eight well-defined homogeneous surfaces) with Monte Carlo simulations of lattice proteins at different concentrations and on surfaces of varying "polarity", we explore the extent and rheological behavior of adsorbed proteins as a function of substrate polarity, "on" rate constants (k(a)) and steric parameters (|A(1)|) from the random sequential adsorption model, and demonstrate a folding to unfolding transition upon adsorption. We show that model globular proteins (hen egg lysozyme, ribonuclease A, and insulin dimer) behave similarly with respect to adsorption. Experimentally, above a substrate wettability cos theta > 0.4 (where theta is the sessile contact angle of water on a substrate in air), the adsorbed mass, rigidity, and k(a) of the proteins are diminished, while the steric factor |A(1)| is increased, suggesting a lower packing density. To analyze these results, we have invoked computer simulations. We show that changing surface polarity has two profound effects. First, the amount adsorbed increases as the surfaces become more apolar. Further, the proteins become less stable as their adsorbed amount increased because they gain a large number of interprotein and protein-surface interactions. Finally, apolar surfaces served to reduce the unfolding free energy barriers, further facilitating the reorganizing of proteins on these surfaces. Thus, increasing the nonpolar nature of the surfaces resulted in a more rigid adsorbed layer, in good agreement with the experiments.
authors.affiliation: Howard P. Isermann Department of Chemical and Biological Engineering and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180-3590, USA.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Anand
authors.forename: Sumit
authors.initials: S
authors.lastname: Sharma
authors.forename: Amit K
authors.initials: AK
authors.lastname: Dutta
authors.forename: Sanat K
authors.initials: SK
authors.lastname: Kumar
authors.forename: Georges
authors.initials: G
authors.lastname: Belfort
mesh_terms: D000327:Adsorption; D007328:Insulin / Q000737:chemistry; D007700:Kinetics; D009010:Monte Carlo Method; D009113:Muramidase / Q000737:chemistry; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D012259:Ribonuclease, Pancreatic / Q000737:chemistry; D013499:Surface Properties; D017155:Wettability
chemical_list: D007328:Insulin; D011506:Proteins; C034329:insulin dimers; D012259:Ribonuclease, Pancreatic; C421864:hen egg lysozyme; D009113:Muramidase