A lipoprotein allosterically activates the CwlD amidase during Clostridioides difficile spore formation

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Spore-forming pathogens like Clostridioides difficile initiate infection through spore germination.
• Spore germination necessitates the degradation of the protective cortex layer, a modified peptidoglycan.
• Cortex degradation relies on muramic-∂-lactam (MAL), a unique peptidoglycan modification recognized by cortex lytic enzymes.

Purpose of the Study:

• To elucidate the regulatory mechanism of CwlD amidase activity by its binding partner, GerS lipoprotein.
• To determine the crystal structure of the CwlD:GerS complex to understand their interaction at a molecular level.

Main Methods:

• X-ray crystallography was employed to solve the structure of the CwlD:GerS complex.
• Biochemical assays were performed to assess CwlD amidase activity and cofactor binding.

Main Results:

• The crystal structure revealed a GerS homodimer bound to two CwlD monomers, with CwlD active sites accessible.
• Unlike other amidase_3 enzymes, CwlD does not stably bind Zn2+ independently.
• GerS binding to CwlD promotes stable Zn2+ binding, which is crucial for CwlD's catalytic function.

Conclusions:

• The study reveals a novel mechanism of bacterial enzyme regulation through the stabilization of a Zn2+ cofactor by a binding partner.
• This finding highlights allosteric regulation by binding partners as a potentially widespread mechanism for controlling bacterial amidase activity.