Structural Architecture

Figure 1: Surface Representation of Collagenase G

Collagenase G is an enzyme of 120kDa and is made up of various domains. The N-terminal end of the protein begins with a pre-domain of varying length which contains a unique export signal that allows the bacteria to secrete the enzyme causing the breakdown of collagen in the host’s muscle. After secretion the short peptide is cleaved creating the mature protein. This is shown in yellow in figure 2 below.

Figure 2: Ribbon representation of the Collagenase module

The Collagenase module spans from Tyr119 - Gly790 and consists of two domains; the activator domain and the peptidase domain. These two domains are connected by a glycine-rich hinge represented in yellow at the top of the molecule (Gly389 – Val397) allowing formation of a two-domain saddle-shaped molecule in its resting state. This hinge region is crucial for collagen binding and subsequent unwinding and processing of the triple-helix.

The peptidase domain is split into two further subdomains, the catalytic subdomain represented in purple and the catalytic helper subdomain represented in cyan, both of which are connected by a linker segment.

Collagenase G also includes various recruitment domains which are not shown in the crystallised collagenase module. These include a polycystic kidney disease-like (PKD-like) domain and one or more collagen-binding domains (CBDs). These C-terminal domains are essential for accurate collagen binding.

Figure 3: Two views of the crystallised structure of the PKD-like domain

The isolated crystal structure of the PKD-like domain (Ala791 – Asn880) shows an adopted two-tiered β-barrel structure with a conserved Trp833 shown in red buried inside the β-barrel. Elimination of the indole ring of Trp833 would destabilise and collapse the barrel structure. This would destroy the necessary structure required for successful collagen binding. This β-barrel framework is also stabilised by a sequence of hydrophobic residues at the interface. The position of the PKD-like domain was found to be at the rear of the molecule behind the catalytic subdomain, with a positional variance of 10Å.

The collagen-binding domains were crystallised previously and their structural information enabled construction of a full-length model of Collagenase G as shown below in figure 4.

Figure 4: Domain organisation of Collagenase G