Tertiary Structure Changes in Albumin Upon Surface Adsorption Observed Via Infrared Spectroscopy
Jack R. Smith, Marcus T. Cicerone, Curtis W. Meuse
A non-destructive infrared (IR) spectroscopy assay is used to measure changes the tertiary structure of Bovine Serum Albumin (BSA) adsorbed to three surfaces: gold, polystyrene (PS) and poly(D,L-Lactic acid) (PDLLA). Polymers are spin-coated onto a gold surface, exposed to protein, then immersed in a deuterated 0.01 M NaPO4 buffer solution. Subsequently, the buffer is removed and an IR beam is reflected from the polymer and protein-coated gold substrate. BSA structure is quantified via changes in the normalized amide II (N-H in plane bend) band intensity. This intensity gives the extent of amide hydrogen-deuterium exchange (HDX) which is directly related to amide solvent exposure. At any exposure time t, the amide II/amide I ratio will increase with unfolding of the protein. The experiment is performed in reflection in order to maximize the signal from the monolayer of adsorbed protein and to provide an experimental configuration that is amenable to exploring a wide range of proteins, polymers and surface structures. Analysis of the results in terms of a single exponential decay. showed that enough amides undergo a measurable amount of exchange in 60 min to quantify relative changes in the tertiary structure of BSA. However, it also showed that substantial fractions undergo HDX at a rate too quick or too slow to measure to be quantified in this experiment. Nevertheless, the proportion of amide groups that belong to these components gave information about relative changes in the tertiary structure of BSA. Adsorption was found to increase the extent of HDX over that observed for BSA in solution, consistent with surface-induced unfolding. The amount of observable exchange was greatest for BSA adsorbed to the surface of PDLLA and least in the case of BSA adsorbed to gold, which indicates the greatest and least degree of unfolding, respectively.
, Cicerone, M.
and Meuse, C.
Tertiary Structure Changes in Albumin Upon Surface Adsorption Observed Via Infrared Spectroscopy, Biomaterials, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852687
(Accessed December 5, 2023)