Conformation dependence of antigenic determinants on the collagen molecule.

Three different types of antigenic determinants were demonstrated in soluble collagen with the aid of rat, rabbit and chicken antisera to native collagen. Helical antigenic determinants which require an intact triple-helical structure of the molecule are mainly recognized by rat antisera. Renaturation of the serologically inactive unfolded polypeptide chains (denatured collagen) is accompanied by a significant recovery of serological activity. Central antigenic determinants which are probably located in the same regions of amino acid sequence are less accessible in the native antigen and become exposed upon denaturation. Equal titres for both types of determinants are found in chicken antisera. Immunization with denatured collagen, however, revealed a response restricted to the central type. Isolated antibodies specific for terminal non-helical antigenic determinants, as yet only known to occur in rabbit antisera, reacted equally well with native collagen, the unfolded polypeptide chains and with small cyanogen bromide peptides. Independence of conformation is therefore suggested for these antigenic structures.