Hydrogen-bonding within the tropocollagen triple helix

Abstract

The chapter discusses the protein stability with emphasis on compact globular proteins representing a single cooperative system. All the small compact globular proteins represent cooperative systems; they exhibit an extreme cooperativity that integrates the whole of their structure into a single structural unit. The large proteins, to which fibrillar proteins are also related, do not present single cooperative systems, but are subdivided into definite cooperative subsystems—structural blocks or domains. The advances in studying the stability of complicated proteins are connected with two methodical achievements: (1) the appearance of the precise scanning microcalorimetric technique, which affords reliable information on the heat capacity function of proteins in a broad temperature range; and (2) realization of the fact that the complicated heat effect of disruption of a complex macromolecular structure can be analyzed thermodynamically. The thermodynamic specificity of collagen has been considered. The volume of globular proteins does not increase at denaturation but decreases, as seen from their ability to denature under high pressure. The results of calorimetric studies are discussed, presenting the specific melting enthalpy of various protein structures—globular proteins, double-stranded coiled coils, and triplestranded coiled coils. The practical importance of thermodynamic studies of protein stability—that is, its importance not only for understanding the principles of organization of these molecules, but just for obtaining structural information on the domain level is emphasized.