THERMODYNAMIC STUDIES OF THE COLLAGEN-LIKE REGION OF HUMAN SUBCOMPONENT-C1Q - A WATER-CONTAINING STRUCTURAL MODEL

Thermal transitions of C1q were investigated by methods of differential scanning calorimetry, circular dichroism and fluorescence. The melting curves of C1q display two pronounced heat absorption peaks which enables determination of the thermodynamic parameters characterizing each transition. The low temperature peak was assigned to melting of the C1q collagenous part. Analysis of the data has revealed unusual, as compared with the monomeric collagen molecules, thermodynamic features of the C1q collagenous part: (1) higher thermal stability strongly dependent on pH; (2) less linear co-operative regions; and (3) a noticeable change in the partial specific heat capacity (ΔCp) in contrast to both the monomeric collagen and the collagen fibrils. This unusually large ΔCp value suggested a conclusion that the fibril-like endpiece of C1q may have a cavity filled with ice-like ordered water molecules. © 1993 Academic Press Limited.