Understanding how natural sequence variation in serum albumin proteins affects conformational stability and protein adsorption

Serum albumins are evolutionary conserved proteins that are found in many animal species, and purified forms are widely used in biotechnology applications, such as components within surface passivation coatings and drug delivery systems. As such, there has long been interest in studying how serum albumins adsorb onto solid supports, although existing studies are limited to one or two species. Herein, we comprehensively investigated three serum albumins of bovine (BSA), human (HSA), and rat (RSA) origin, and discovered striking differences in their conformational stabilities and adsorption properties. Together with bioinformatics analysis, dynamic light scattering (DLS) and circular dichroism (CD) spectroscopy measurements revealed that the proteins form different types of macromolecular assemblies in solution. BSA and HSA existed as individual monomers while RSA formed multimers, and each protein exhibited sequence-dependent variations in conformational stability as well. Quartz crystal microbalance-dissipation (QCM-D) and localized surface plasmon resonance (LSPR) experiments further showed that BSA and HSA proteins adsorb to form well-packed adlayers, and the extent of protein uptake and spreading depended on their unique conformational stabilities. Conversely, RSA adsorption resulted in sparse adlayers and appreciably less spreading of the adsorbed multimers, as confirmed by attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy experiments. Together, our findings demonstrate that significant differences in conformational stability and adsorption behavior exist even between evolutionary conserved serum albumins with high sequence and structural similarity and illustrate how rational engineering of protein structures and stabilities, guided by insights from nature, might be useful to design protein-based coatings for various biointerfacial science applications.