STRUCTURAL IMPLICATIONS FOR THE ROLE OF THE N-TERMINUS IN THE SUPERACTIVATION OF COLLAGENASES - A CRYSTALLOGRAPHIC STUDY

For the collagenases PMNL-CL and FIB-CL, the presence of the N-terminal Phe(79) correlates with an increase in proteolytic activity. We have determined the X-ray crystal structure of the recombinant Phe(79)-Gly(242) Catalytic domain of human neutrophil collagenase (PMNL-CL, MMP-8) using the recently solved model of the Met(80)-Gly(242) form for phasing and subsequently refined it to a final crystalographic R-factor of 18.0% at 2.5 Angstrom resolution. The PMNL-CL catalytic domain is a spherical molecule with a flat active site cleft separating a smaller C-terminal subdomain from a bigger N-terminal domain, that harbours two zinc ions, namely a 'structural' and a 'catalytic' zinc, and two calcium ions. The N-terminal segment prior to Pro(86), which is disordered in the Met(80)-Gly(242) form, packs against a concave hydrophobic surface made by the C-terminal helix. The N-terminal Phe(79) ammonium group makes a salt link with the side chain carboxylate group of the strictly conserved Asp(232). Stabilization of the catalytic site might be conferred via strong hydrogen bonds made by the adjacent, likewise strictly conserved Asp(233) With the characteristic 'Met-turn', which forms the base of the active site residues.