FIGURE 2.

Initial steps of collagenolysis (59). A, closed (left) and open/extended (right) forms of full-length MMP-1 in equilibrium. B, the extended protein binds α1(I)-(772–786) THP chains 1T-2T at Val²³–Leu²⁶ with the HPX domain and the residues around the cleavage site with the CAT domain. The THP is still in a compact conformation. C, closed full-length MMP-1 interacting with the released 1T chain (magenta). D, after hydrolysis, both peptide fragments (C- and N-terminal) are initially bound to the active site. E, the C-terminal region of the N-terminal peptide fragment is released. This figure has been reprinted with permission from the Journal of the American Chemical Society.