A collagen-like glycoprotein of the extracellular matrix is the undegraded form of type VI collagen.

The 140 000-dalton collagenous glycoprotein (CGP) from calf aorta and ligament characterized by Gibson & Cleary (1982) [Gibson, M.A., & Cleary, E.G. (1982) Biochem. Biophys. Res. Commun. 105, 1288-1295] has been studied. In the electron microscope, rotary-shadowed CGP molecules appear similar to the dimers of type VI collagen (short-chain collagen, intima collagen) described by other authors [Furthmayr, H., Wiedemann, H., Timpl, R., Odermatt, E., & Engel, J. (1983) Biochem. J. 211, 303-311] except that they have larger globular domains. As shown by gel electrophoresis, pepsin treatment of CGP at 4 degrees C either before or after reduction releases polypeptide chains corresponding in size to those of type VI collagen. Electron microscopic examination shows that pepsin digestion of nonreduced CGP removes the outer globular domains, reduces the size of the inner ones, and separates the paired central strands. The residual structures look like type VI collagen dimers. When intact CGP is reduced, monomers with two large globular ends are obtained. Pepsin digestion of monomers removes most or all of both globular domains. In immunoblots, CGP and its pepsin-derived fragments react with antibodies directed against type VI collagen. The results indicate that type VI collagen is an integral component of CGP.