Comparison of the thermal stabilization of proteins by oligosaccharides and monosaccharide mixtures: Measurement and analysis in the context of excluded volume theory

Abstract

The thermal stability of apo α–lactalbumin (α–LA) and lysozyme was measured in the presence of mixtures of glucose, fructose, and galactose. Mixtures of these monosaccharides in the appropriate stoichiometric ratio were found to have a greater stabilizing effect on each of the two proteins than equal weight/volume concentrations of di- tri- and tetrasaccharides with identical subunit composition (sucrose, trehalose, raffinose, and stachyose). The excluded volume model for the effect of a single saccharide on the stability of a protein previously proposed by Beg et al. [Biochemistry 54 (2015) 3594] was extended to treat the case of saccharide mixtures. The extended model predicts quantitatively the stabilizing effect of all monosaccharide mixtures on α–LA and lysozyme reported here, as well as previously published results obtained for ribonuclease A [Biophys. Chem. 138 (2008) 120] to within experimental uncertainty.