Proteins don’t always behave the way they do in their natural environment when studied in the aqueous buffers most methods call for. This is why researchers often wish to characterize protein functionality in complex mixtures that closely resemble the protein’s natural environment. But sadly, it’s very difficult to accomplish. It requires working with methods and instruments that can measure the biophysical characteristics of the protein in bioliquids such as plasma or serum. And when it comes to measuring how proteins interact with binding partners, the list of methods that can do it, well it’s a very short one.
In this article, scientists used MST to characterize the interaction between two single-residue variants of SERPINA1 and their primary target, human neutrophil elastase, in conditions that mimic their natural environment in human plasma. The significant differences observed between the affinity of both variants for their target contrast with previous studies performed with purified proteins in simple protein- and lipid-free buffer systems, in which no differences in binding affinities could be distinguished. To add even more significance to the study, the authors add that this functionally relevant coding sequence variation confers risk for large artery atherosclerotic stroke.
These experiments provide evidence on the influence of test environments on the strength of protein interactions and thus in the results of a binding assay. Moreover, they demonstrate the capability of MST to quantify binding affinities in complex bioliquids, something very few other methods can do.