Aghajari, N. | Search bioRxiv

bioRxiv2026

Screening for Polysaccharide Utilization Loci Targeting Marine Polysaccharides

Polysaccharide utilization loci (PULs) have been a goldmine for the characterization of novel carbohydrate active enzymes (CAZymes) and the understanding of their synergistic degradation of complex polysaccharides. We collected PUL predictions containing CAZymes from glycoside hydrolase families GH29, GH50 and GH117, expected to participate in marine polysaccharide breakdown. We explored the evolutionary diversity in these families in terms of sequences and PUL composition, based on sulfatases and CAZymes. From 41 selected PULs, more than 400 putative enzymes were produced, purified and screened on a large collection of carbohydrates. We attributed a function to more than 130 enzymes from five sulfatase subfamilies, 29 known CAZymes families and discovered an activity for 4 families previously of unknown function, including an -L-galactosidase structurally and functionally characterized with mutants. Finally, our detailed analysis of the enzymatic synergies in five PULs, two targeting marine polysaccharides and three targeting eukaryotic polysaccharides, by marine and human gut organisms, highlight the efficiency of our exploratory strategy.

biochemistry↗

bioRxiv2019

Interactions of helices on interdomain interface couple the chemistry of intermediate formation with allostery in Plasmodium falciparum GMP synthetase

GMP synthetase catalyzes the substitution of the C2 oxo-group of the purine base in XMP with an amino-group generating GMP, the last step in the biosynthesis of GMP. This reaction involves a series of catalytic events that include hydrolysis of Gln generating ammonia in the glutamine amidotransferase (GATase) domain, activation of XMP to adenyl-XMP intermediate in the ATP pyrophosphatase (ATPPase) domain and reaction of ammonia with the intermediate to generate GMP. Inherent to the functioning of GMP synthetases is bidirectional domain crosstalk, which leads to allosteric activation of the GATase domain by substrates binding to the ATPPase domain, synchronization of the two catalytic events and tunnelling of ammonia from the GATase to the ATPPase domain. Herein, we have taken recourse to the analysis of structures of GMP synthetases, site-directed mutagenesis and, steady-state and transient kinetic assays on the Plasmodium falciparum enzyme to decipher the molecular basis of catalysis in the ATPPase domain and domain crosstalk. The results map the residues critical for catalysis in the ATPPase domain to the helices 11 and 12 that are located at the interdomain interface, and the lid-loop that follows 11. This apart, perturbing interdomain interactions involving residues on 11 and 12 impairs GATase activation. These results imply that this arrangement of helices at the domain interface with residues that play roles in ATPPase catalysis as well as domain crosstalk enables coupling ATPPase catalysis with GATase activation. Overall, the study enhances our understanding of GMP synthetases, which are drug targets in many infectious pathogens.

biochemistry↗