Does the triple helical domain of type I collagen encode molecular recognition and fiber assembly while telopeptides serve as catalytic domains? Effect of proteolytic cleavage on fibrillogenesis and on collagen-collagen interaction in fibers

Over the last several decades, it has been established that proteolytic rem oval of short, non-helical terminal peptides (telopeptides) from type I col lagen significantly alters the kinetics of in vitro fibrillogenesis. Howeve r, it has also been observed that the protein is still capable of forming f ibers even after complete removal of telopeptides. This study focuses on th e characterization of this fibrillogenesis competency of collagen, We have combined traditional kinetic and thermodynamic assays of fibrillogenesis ef ficacy with direct measurements of interaction between collagen molecules i n fibers by osmotic stress and x-ray diffraction. We found that telopeptide cleavage by pepsin or by up to 20 h of Pronase treatment altered fiber ass embly kinetics, but the same fraction of the protein still assembled into f ibers. Small-angle x-ray diffraction showed that these fibers have normal, native-like D-stagger. Force measurements indicated that collagen-collagen interactions in fibers were not affected by either pepsin or Pronase treatm ent, In contrast, prolonged (>20 h) Pronase treatment resulted in cleavage of the triple helical domain as indicated by SDS-polyacrylamide gel electro phoresis. The triple-helix cleavage correlated with the observed decrease i n the fraction of protein capable of forming fibers and with the measured l oss of attraction between helices in fibers, These data suggest that telope ptides play a catalytic role, whereas the information necessary for proper molecular recognition and fiber assembly is encoded in the triple helical d omain of collagen.