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The C‐terminal extrahelical peptide of type I collagen and its role in fibrillogenesis in vitro
Author(s) -
Capaldi Michael J.,
Chapman John A.
Publication year - 1982
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360211115
Subject(s) - chemistry , fibril , fibrillogenesis , pepsin , peptide , edman degradation , carboxypeptidase , biochemistry , digestion (alchemy) , biophysics , destabilisation , type i collagen , peptide sequence , enzyme , chromatography , medicine , psychology , social psychology , pathology , biology , gene
Abstract The formation in vitro of fibrils from type I acid‐soluble calf skin collagen has been studied before and after removal of the extrahelical peptides with carboxypeptidase and with pepsin. Turbidimetric studies show that the mechanism of fibril growth in undigested collagen is similar to that in pepsin‐digested collagen; following carboxypeptidase digestion, however, a different growth mechanism was apparent. The two mechanisms have been further characterized by electron microscopy. In the course of formation of fibrils from undigested collagen, “early fibrils” (short D ‐periodic fibrils that have both ends visible) occurred in the lag phase under the precipitating conditions employed here. After pepsin or carboxypeptidase digestion of the collagen no “early fibrils” were seen. In carboxypeptidase‐digested collagen, lateral assembly was inhibited; after pepsin digestion, linear assembly was inhibited. Complete removal of the extrahelical peptides prevented fibril formation under the conditions used here. Electron‐optical examination of segment‐long‐spacing (SLS) dimers established a more complete removal of the C‐terminal peptide after carboxypeptidase digestion than after pepsin digestion. Analyses of staining patterns of SLS dimers and fibrils from undigested and digested samples showed that the C‐terminal peptide in SLS crystallites and fibrils formed from undigested collagen is in a condensed conformation. A proposed conformation, in which condensation occurs predominantly in a hydrophobic region at the proximal end of the C‐terminal peptide, is discussed in terms of a dual role for the C‐terminal peptide in fibrillogenesis. One role, shared with the N‐terminal peptide, is to participate in interactions between the 4 D ‐staggered molecules leading to the formation of linear aggregates; the other is to participate in interactions between these linear aggregates giving rise to D ‐periodic aggregates and lateral (as well as linear) growth.