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-termina l 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 pha sing and subsequently refined it to a final crystalographic R-factor o f 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 tw o zinc ions, namely a 'structural' and a 'catalytic' zinc, and two cal cium ions. The N-terminal segment prior to Pro(86), which is disordere d in the Met(80)-Gly(242) form, packs against a concave hydrophobic su rface made by the C-terminal helix. The N-terminal Phe(79) ammonium gr oup makes a salt link with the side chain carboxylate group of the str ictly conserved Asp(232). Stabilization of the catalytic site might be conferred via strong hydrogen bonds made by the adjacent, likewise st rictly conserved Asp(233) With the characteristic 'Met-turn', which fo rms the base of the active site residues.