Differential unfolding of α1 and α2 chains in type I collagen and collagenolysis

Collagenolysis plays a central role in many disease processes and a detailed understanding of the mechanism of collagen degradation is of immense interest. While a considerable body of information about collagenolysis exists, the details of the underlying molecular mechanism are unclear. Therefore, to further our understanding of the precise mechanism of collagen degradation, we used molecular dynamics simulations to explore the structure of human type I collagen in the vicinity of the collagenase cleavage site. Sit-ice post-translational proline hydroxylation is an important step in the synthesis of collagen chains, we used the DNA sequence for the alpha 1 and alpha 2 chains of human type I collagen, and the known amino acid sequences for bovine and chicken type I collagen, to infer which prolines are hydroxylated in the vicinity of the collagenase cleavage site. Simulations of type I collagen in this region suggest that partial unfolding of the alpha 2 chain is energetically preferred relative to unfolding of alpha 1 chains. Localized unfolding of the a2 chain leads to the formation of a structure that has disrupted hydrogen bonds N-terminal to the collagenase cleavage site. Our data suggest that this disruption in hydrogen bonding pattern leads to increased chain flexibility, thereby enabling the alpha 2 chain to sample different partially unfolded states. Surprisingly, our data also imply that alpha 2 chain unfolding is mediated by the non-hydroxylation of a proline residue that is N-terminal to the cleavage site in alpha 1 chains. These results suggest that hydroxylation on one chain (alpha 1) can affect the structure of another chain (alpha 2), and point to a critical role for the non-hydroxylation of proline residues near the collagenase cleavage site. (C) 2008 Elsevier Ltd. All rights reserved.