Supramolecular Thermodynamics

JAMES R. LEPOCK (University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada)

Abstract for 1998 American Association for the Advancement of Science (AAAS) Annual Meeting and Science Innovation Exposition Philadelphia, Pennsylvania Monday, February 16, 1998, 3:00pm-6:00pm Track: Emerging Science: Transforming the Next Generation Session number: 101.0

Thermodynamics has played a major role in understanding the stability and folding of isolated, pure proteins; however, until recently it has not been used directly on proteins under physiological conditions in intact cells. A quantitative measure of the conformational stability of proteins, the Gibbs free energy of folding , can be determined from reversible thermodynamics. Proteins undergo order-disorder transitions, which are detectable in differential scanning calorimetry (DSC) profiles of specific heat vs. temperature. The major contribution to vs. T profiles of whole cells is protein unfolding, and for cellular proteins can be calculated from the transition temperature and enthalpy , both of which can be determined by DSC. For supramolecular structures to form in cells, specific interactions between proteins must occur. The strength of these interactions is given by the free energy of interaction , which can be determined by DSC. Interprotein interactions must increase the conformational stability of the individual protein components. Specificity of interaction is related to , and information theory can be used to predict the minimum needed for one cellular protein to precisely recognize another. Consequences are that supramolecular structures must be more stable than the protein components and that more precise recognition (i.e. greater specificity) requires a more stable supramolecular structure.