Cold denaturation of encapsulated ubiquitin.

Theoretical considerations suggest that protein cold denaturation can potentially provide a means to explore the cooperative substructure of proteins. Protein cold denaturation is generally predicted to occur well-below the freezing point of water. Here NMR spectroscopy of ubiquitin encapsulated in reverse micelles dissolved in low viscosity alkanes is used to follow cold-induced unfolding to temperatures below −25 °C. Comparison of cold-induced structural transitions in a variety of reverse micelle-buffer systems indicate that protein-surfactant interactions are negligible and allow the direct observation of the multi-state cold-induced unfolding of the protein.