A materials science framework for connecting protein stability with surface adsorption and coating applications

• Main Author: Ma, Gamaliel Junren
• Other Authors: Cho Nam-Joon
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials::Biomaterials; Engineering::Nanotechnology
• Online Access: https://hdl.handle.net/10356/154985
• Institution: Nanyang Technological University

The formation of protein coatings at the solid-liquid interface via protein adsorption is broadly relevant for various materials science and biomedical applications such as implantable biomedical devices, biosensors and nanomedicine. The noncovalent adsorption behavior of protein molecules is governed by various interfacial forces between the protein molecule in solution and the solid surface, as well as by intramolecular forces which determine a protein’s folded structure and solution-phase conformational stability. Although a protein’s conformational stability has been closely linked to its extent of unfolding in the adsorbed state, it remains to be understood how this relationship may be exploited in order to control a protein’s adsorption behavior and adlayer properties to suit specific application needs. The objective of this thesis is to systematically interrogate the relationship between protein conformational stability and protein adsorption behavior such as adsorption uptake, adsorption rate, and the degree of adsorption-related denaturation and spreading. The overall hypothesis is that rationally tuning the conformational stability of protein molecules based on materials science concepts can influence protein adsorption and that the insights gained from this framework can be used to engineer improved protein coating applications. To test this hypothesis, serum albumins as model proteins with modulated conformational stabilities based on their structure and processing, in line with the materials science paradigm, were comparatively evaluated using an experimental approach that characterized the proteins’ solution-phase conformational stabilities by measuring their temperature-dependent aggregation profiles and degree of secondary structural unfolding, and also that which characterized the proteins’ adsorption behavior by measuring their adsorption uptake, adsorption rate and extent of surface-induced denaturation. It was revealed that primary structure variations between serum albumin proteins from different species affected protein conformational stability and adsorption behavior, and that bovine serum albumin (BSA) possessed the lowest conformational stability and greatest adsorption-related denaturation compared to that of human and rat origin. This provided mechanistic reasons for why BSA is so widely used in surface passivation (“blocking”) protocols for many biotechnological applications. A further investigation on several commercially available and differently processed BSA proteins revealed that they possessed significantly different conformational stabilities and adsorption behavior, depending on whether or not a purification step which removed fatty acids was performed. It was further determined that the doping of BSA proteins with fatty acids and other related amphipathic molecules generally increased protein conformational stability and could either increase or decrease adsorption uptake in a concentration-dependent manner, depending on the chemical structure of the amphipathic molecules and their binding strength with BSA protein. Finally, the experimentally observed differences in conformational properties and adsorption behavior of certain types of BSA proteins were correlated with their surface passivation performance. In summary, the findings in this thesis presented how materials science concepts can be used to rationalize the relationship between protein conformational stability and adsorption behavior and offer a broadly applicable approach to engineer protein coatings for various useful applications.