Energetics and Thermodynamics of Collagen Self-Assembly
The structure of collagen is characterized by the hierarchical order of self-assembly of its constituent units. Physicochemical methods, including thermodynamic measurements and considerations of energetics have been used to study the structure and conformation of the polypeptide chains, the formation and stability of the triple helix, and, to a lesser extent, the association of triple helices. This chapter deals with these levels of self-assembly mainly from the relationships between structure and the energetics of noncovalent interactions. The conformational properties of the polypeptide chains in collagen and the interactions that determine conformation and assembly are the same as those that govern the folding of globular proteins. Upon heating, collagen and collagen-like poly(tripeptide)s undergo a transition over a narrow temperature range. The enthalpy of melting of monodisperse solutions has been determined by calorimetry for many collagen species and for synthetic model analogs. The effect of salts and denaturants on collagen melting is similar to their effect on the denaturation of globular proteins.