Tangled Up in Fibers: How a Multidomain Lytic Polysaccharide Monooxygenase Binds Its Chitin Substrate

Area of Science:

• Biochemistry
• Microbiology
• Structural Biology

Background:

• Lytic polysaccharide monooxygenases (LPMOs) are key enzymes for degrading insoluble carbohydrates like chitin and cellulose.
• Their application in biofuel and bioplastics production is significant, but their interfacial activity poses characterization challenges.
• The four-domain LPMO, GbpA from *Vibrio cholerae*, interacts with chitin via its terminal domains.

Purpose of the Study:

• To elucidate the docking mechanism of the LPMO GbpA onto its insoluble substrate, chitin.
• To overcome challenges in studying enzyme-substrate interactions at the solution-insoluble interface.
• To understand the role of GbpA in bacterial interactions with chitinous materials.

Main Methods:

• Developed a protocol for stable GbpA-chitin complex formation in suspension.
• Utilized small-angle neutron scattering (SANS) after determining the chitin contrast match point (47% D2O).
• Complemented SANS data with negative-stain electron microscopy to characterize the mesoscale structure.

Main Results:

• GbpA rapidly binds to chitin fibers, coating and smoothing their surface.
• GbpA binding can induce the formation of protein-chitin clumps with numerous GbpA molecules.
• The enzyme's interaction effectively prepares the substrate for bacterial microcolony formation.

Conclusions:

• GbpA's interaction with chitin involves surface coating and aggregation, facilitating bacterial colonization.
• The study provides insights into the structural basis of LPMO activity at insoluble interfaces.
• Findings suggest a mechanism for how GbpA promotes bacterial microcolony development on chitin.