Thermodynamics of Concanavalin A Self-Association in the Presence of Osmolytes

Abstract

Protein-protein interactions are critical for biological function and depend significantly on environmental factors. A wide variety of small organic molecules that comprise the cellular environment are capable of interacting with proteins to affect folding, binding, and association. The plant lectin concanavalin A (ConA) undergoes a reversible, pH dependent dimer-to-tetramer equilibrium and has been used in our laboratory as a model system to study the effect of osmolytes on protein self-association. Previous research determined that trimethylamine N-oxide (TMAO) stabilizes the tetrameric conformation, while urea favors the dimer. Studying the equilibrium over a range of temperatures allowed quantification of the enthalpy change (∆H) and entropy change (∆S) of tetramer formation. Urea increased both the ∆H and ∆S of tetramer formation, while TMAO decreased both. These effects are consistent with preferential hydration of the dimer-dimer interface in TMAO solution and preferential binding of urea to the interface. KEYWORDS: Concanavalin A; Osmolytes; Trimethylamine N-oxide; Urea; Protein-Protein Interaction; Equilibrium; Enthalpy; Preferential Hydration