Trimeric assembly and three-dimensional structure model of the FACIT collagen COL1-NC1 junction from CD and NMR analysis

The 3D structure of the COL1-NC1 junction of FACIT type XIV collagen was investigated using GYCDPSSCAG and (GPP*)(3)GYCDPSSCAG synthetic peptides, circular dichroism, and NMR. At -20 degrees C and under air oxidation catalyzed by Cu2+, the peptide (GPP*)(3)GYCDPSSCAG is able to self-associate with high yield into a stable triple disulfide bonded trimer. The presence of a triple helical conformation was confirmed by circular dichroism. The analysis of the trimer by 2D NMR provided a set of distance constraints for the noncollagenous part. Molecular models for the 3D structure of COL1-NC1 junction were calculated, using the NMR distance constraints in combination with the 3D structural data recently established by X-ray crystallography [Bella, J., Eaten, M., Brodsky, B., & Berman, H. M. (1994) Science 266, 75-81] for a collagenous triple helix. From the eight theoretically possible arrangements for the three interchain disulfide bonds, only two close disulfide conformers are compatible with the experimental data. The main feature of the trimer structure is the asymmetry of the molecule due to the disulfide bond pattern that induces a particular folding of one chain. This chain forms a turn-like structure locked by two disulfide bonds with the two other chains. The turn-like folding is close to that observed for the cyclized oxidized monomeric peptide. This is the first report of the 3D structure model for a junction between a collagenous triple helical domain and a noncollagenous domain.