Poster Sessions

Biophys-2

Elena Makareeva

E. Makareeva, E. L. Mertz, N. V. Kuznetsova, M. B. Sutter, A. M. DeRidder, J. C. Vera, W. A. Cabral, A. M. Barnes, D. J. McBride, J. C. Marini, S. Leikin

Structural Heterogeneity of Type I Collagen Triple Helix and Its Role in Osteogenesis Imperfecta

Gly substitutions in type I collagen cause over 80% of severe OI cases, suggesting that structural defects in the triple helix underlie the disease. However, no simple correlations of OI severity with the predicted or measured triple helix stability have been reported. To test whether location of mutation within different structural regions in the triple helix may modulate the OI phenotype, we mapped these regions by systematic measurements of mutant collagen stability. Using differential scanning calorimetry and circular dichroism, we measured variation in the collagen melting temperature (Tm) for 50 different Gly substitutions from OI patients. Using infrared spectroscopy and known stabilities of collagen-like peptides, we determined variation in the activation energy for local triple helix unfolding. Combining the resulting Tm and local stability maps, we delineated three flexible regions and two stable regions in type I collagen triple helix. The flexible regions overlapped with regions important for collagen fibril assembly and ligand binding. One of them coincided with the largest known region of lethal alpha1(I) Gly substitutions. We found that mutations within the stable N-terminal region cooperatively unfold this region and prevent normal N-propeptide cleavage. The uncleaved pN-collagen incorporates into fibrils and leads to the distinctive OI/EDS phenotype.