Download MendeleyConstrained Catalytic Itinerary of a Retaining 3,6-Anhydro-D-Galactosidase, a Key Enzyme in Red Algal Cell Wall Degradation.
Wallace, M.D., Cuxart, I., Roret, T., Guee, L., Debowski, A.W., Czjzek, M., Rovira, C., Stubbs, K.A., Ficko-Blean, E.(2024) Angew Chem Int Ed Engl 63: e202411171-e202411171
- PubMed: 39022920
- DOI: https://doi.org/10.1002/anie.202411171
- Primary Citation of Related Structures:
8RZG, 8RZH, 8RZI, 8RZJ, 8RZK - PubMed Abstract:
The marine Bacteroidota Zobellia galactanivorans has a polysaccharide utilization locus dedicated to the catabolism of the red algal cell wall galactan carrageenan and its unique and industrially important α-3,6-anhydro-D-galactose (ADG) monosaccharide. Here we present the first analysis of the specific molecular interactions the exo-(α-1,3)-3,6-anhydro-D-galactosidase ZgGH129 uses to cope with the strict steric restrictions imposed by its bicyclic ADG substrate - which is ring flipped relative to D-galactose. Crystallographic snapshots of key catalytic states obtained with the natural substrate and novel chemical tools designed to mimic species along the reaction coordinate, together with quantum mechanics/molecular mechanics (QM/MM) metadynamics methods and kinetic studies, demonstrate a retaining mechanism where the second step is rate limiting. The conformational landscape of the constrained 3,6-anhydro-D-galactopyranose ring proceeds through enzyme glycosylation B1,4 → [E4]‡ → E4/1C4 and deglycosylation E4/1C4 → [E4]‡ → B1,4 itineraries limited to the Southern Hemisphere of the Cremer-Pople sphere. These results demonstrate the conformational changes throughout catalysis in a non-standard, sterically restrained, bicyclic monosaccharide and provide a molecular framework for mechanism-based inhibitor design for anhydro-type carbohydrate-processing enzymes and for future applications involving carrageenan degradation. In addition, it provides a rare example of distinct niche-based conformational itineraries within the same carbohydrate-active enzyme family.
Organizational Affiliation:
University of Western Australia School of Molecular Sciences, School of Molecular Sciences, AUSTRALIA.
