Catalytic Zinc Site

The central helix of the TLP fold spans Leu517 – Leu534, as indicated in figure 2. This contains the zinc binding site that is situated in a 523–HEXXH–527 motif. The catalytic Zn²⁺ is tetrahedrally coordinated by the side chains of His523, His527 and Glu555 of the central helix, as well as a water molecule that is further hydrogen-bonded to the general base Glu524. Glu555 resides on a neighbouring upstream helix. The water molecule is essential in forming the nucleophile on Collagenase activation during catalysis. The positioning of the catalytic zinc is portrayed in figures 3 and 4.



Figure 1: Molecular surface of catalytic site

 



Figure 2: Central helix of TLP fold, defining the protein as a member
of the gluzincin family

 



Figure 3: Coordination of zinc atom in catlytic site

 




Figure 4: Tetrahedral orientation of zinc atom in catlytic site

  

The crystallised structure of ColG was produced in a zinc-depleted form. This suggests that the zinc binding is atypically weak, with ligating distances of that shown below in figure 5. 



Figure 5: Ligating bond distances in the catalytic site