Antigenic structure of the aminoterminal region in type I procollagen: Characterization of sequential and conformational determinants

Abstract

Antibodies to calf or sheep skin procollagen, to its consitituent pα1(I) and pα2 chain or to peptide fragments from the aminoterminal region in pα1(I) were studied by radioimmune assays using various 1250-labeled antigens. The highest antibody response was obtained against the globular region in pα1(I). The adjacent precursor-specific collagenous and non-helical domains may modulate the antigenicity of the globular determinants but are themselves only weak antigens. No antigenic determinants were detected in the pα2 chain. Antibodies to pα1(I) chain did not cross-react with pα2 or pα1(III) chains. Antisera against the globular procollagen peptide showed no difference between the peptide and procollagen indicating that the release of the globular region from pα1(I) by collagenase is not accompanied by large conformational alterations. Complete cross-reaction was observed between precursor-specific peptides obtained from calf or sheep procollagen. Reduction and S-carboxymethylation of the five disulfide bridges in the globular region largely destroyed antigenicity. However, a minor fraction of the antibodies against the native peptide could still react with the unfolded peptide. Determinants recognized in this reaction are apparently shared by the native and unfolded peptide and were stable towards trypsin. On the other hand, antibodies prepared against the reduced and alkylated procollagen peptide did not react with the native peptide. The data indicate that that globular regions in pα1(I) chain possesses both conformational and sequential determinants which differ considerably in their immunogenic capacity.