ANOTHER LOOK AT COLLAGEN-V AND COLLAGEN-XI MOLECULES

The fibrillar collagens are the most abundant proteins of extracellula r matrices. Among them, collagens V and XI are quantitatively minor co mponents which participate in the formation of the fibrillar collagen network. Since these collagens were discovered, studies have demonstra ted that they may play a fundamental role in the control of fibrilloge nesis, probably by forming a core within the fibrils. Ano ther charact eristic of these collagens is the partial retention of their N-propept ide extensions in tissue forms, an unusual observation in comparison t o the other known fibrillar collagens. The tissue locations of collage ns V and XI are different, but their structural and biological propert ies seem to be closely related. It has been shown that their primary s tructures are highly conserved at both the gene and protein levels, an d that these conserved features are the bases of their similar biologi cal properties. In particular, they are both resistant to mammalian co llagenases, and surprisingly sensitive to trypsin treatment. Collagens V and XI are usually buried within the major collagen fibrils, althou gh they have both cell adhesion and heparin binding sites which could be of crucial importance in physiological processes such as developmen t and wound healing. It has became evident that several molecules are in fact heterotypic associations of chains from both collagens V and X I, demonstrating that these two collagens are not distinct types but a single type which can be called collagen V/XI.