Domain Assembly

The activator domain spans from Tyr119 – Asp388 and consists of an array of 12 parallel α-helices. The N-terminal flap of the saddle begins with a distorted helical pair (Tyr119 – Lys161) represented in red followed by ten tandemly repeated HEAT motifs represented as purple cylindrical helices below in figure 1. The HEAT domain consists of repeats of around 47 residues that form two anti-parallel α-helices and two turns arranged around a common axis. These structures are very flexible and contain conserved Asp and Arg residues at positions 19 and 25 respectively of each domain. These HEAT repeats are important for interacting with collagen and initiating its unwinding.



Figure 1: Structural architecture of the activation domain



The peptidase domain begins with the catalytic subdomain ranging from residues Asp398 – Gln669, adopting a thermolysin-like peptidase (TLP) fold. The central helix of the TLP fold that contains the catalytic site is represented in cyan and it is this structural architecture that defines Collagenase G as a member of the Gluzincin family. These family members bind a single catalytic zinc ion that is tetrahedrally coordinated by three amino acid ligands and a water molecule. The following page explains the structural organisation of the catalytic site.



Figure 2: Structural architecture of the peptidase domain

A linking segment represented in yellow consists of 8 residues (Glu670 – Asp678) which connects the catalytic subdomain to the catalytic helper subdomain. The catalytic subdomain forms the rest of the peptidase domain spanning residues Asp679 – Asp788. The catalytic subdomain includes an array of antiparallel β-sheets that are covered by two α-helices that protect the protein’s interior from the solvent.