Structural basis for the regulation of β-glucuronidase expression by human gut Enterobacteriaceae

Abstract

The gut microbiota harbor diverse β-glucuronidase (GUS) enzymes that liberate glucuronic acid (GlcA) sugars from small-molecule conjugates and complex carbohydrates. However, only the Enterobacteriaceae family of human gut-associated Proteobacteria maintain a GUS operon under the transcriptional control of a glucuronide repressor, GusR. Despite its potential importance in ,, ,, and opportunistic pathogens, the structure of GusR has not been examined. Here, we explore the molecular basis for GusR-mediated regulation of GUS expression in response to small-molecule glucuronides. Presented are 2.1-Å-resolution crystal structures of GusRs from and in complexes with a glucuronide ligand. The GusR-specific DNA operator site in the regulatory region of the GUS operon is identified, and structure-guided GusR mutants pinpoint the residues essential for DNA binding and glucuronide recognition. Interestingly, the endobiotic estradiol-17-glucuronide and the xenobiotic indomethacin-acyl-glucuronide are found to exhibit markedly differential binding to these GusR orthologs. Using structure-guided mutations, we are able to transfer GusR's preferential DNA and glucuronide binding affinity to GusR. Structures of putative GusR orthologs from GUS-encoding Firmicutes species also reveal functionally unique features of the Enterobacteriaceae GusRs. Finally, dominant-negative GusR variants are validated in cell-based studies. These data provide a molecular framework toward understanding the control of glucuronide utilization by opportunistic pathogens in the human gut.

Regulation of alginate catabolism involves a GntR family repressor in the marine flavobacterium Zobellia galactanivorans DsijT

“…AusR best BLAST hit against the characterized protein database UniprotKB/Swiss-prot was LutR from Bacillus subtilis strain 168 (accession O07007, 31.6% sequence identity, e-value 2.10 −23 ) that negatively regulates L-lactate utilization. The closest structurally characterized homolog to Z. galactanivorans AusR was a GntR-like regulator from Streptococcus agalactiae (PDB accession 6AZ6, 30.6% sequence identity, e-value 1.10 −13 ) encoded in a genomic cluster dedicated to the degradation of glucuronated substrates that notably comprises genes for 2-keto-3-deoxy-gluconate kinase, β-D-glucuronidase and uronate isomerase ( 60 ).…”

Targeted inhibition of gut bacterial β-glucuronidase activity enhances anticancer drug efficacy

“…Indeed, we were intrigued to see that Proteobacteria levels in athymic mice can be reduced 10-fold (4 to >0.4%) via GUS inhibition even in mice not receiving irinotecan. Proteobacteria, specifically the Enterobacteriaceae, are unique among gut microbial taxa in encoding an operon of genes encoding GUS enzymes that are up-regulated in response to the presence of glucuronidated compounds, allowing these bacterial species to use GlcA for growth (31). By inhibiting Enterobacteriaceae GUS enzymes and blocking access to GlcA, GUSi alone seems capable of blunting the growth of Proteobacteria in the mouse GI tract.…”

Pharmacological Activation of PXR and CAR Downregulates Distinct Bile Acid-Metabolizing Intestinal Bacteria and Alters Bile Acid Homeostasis

“…Characterization of these microbial enzymes has led to better understanding of the pharmacokinetics of digoxin as well as improved efficacy and safety (Haiser et al, 2013(Haiser et al, , 2014Koppel et al, 2018). Furthermore, microbial b-glucoronidases deconjugate host Phase-II glucuronidation metabolites and modulate the potential toxicity of circulating endogenous and xenobiotic compounds (Little et al, 2018;Pollet et al, 2017;Wallace et al, 2015).…”