Molecular mechanism of plasmid-borne resistance to sulfonamides

Abstract

The sulfonamides (sulfas) are the oldest class of synthetic antibacterial that target the essential, conserved dihydropteroate synthase (DHPS) enzyme, encoded by folP, through chemical mimicry of its substrate p-aminobenzoic acid (pABA). Resistance has complicated their clinical utility and is widespread in pathogenic species. Resistance is mediated by acquisition of sul genes on mobile genetic elements, which code for the so-called Sul enzymes that are divergent DHPS enzymes with intrinsic sulfa-insensitivity. Even decades after the discovery of this resistance mechanism, its molecular details have not been understood. In this study, we elucidate the molecular basis for intrinsic resistance of Sul enzymes using x-ray crystallography, enzymology, mutagenesis, intrinsic tryptophan fluorescence, antibiotic susceptibility of a contemporary ΔfolP strain, and adaptive laboratory evolution of folP. We show that the active sites of Sul enzymes possess a modified pABA-interaction region based on insertion of a Phe-Gly sequence. This insertion is necessary for discrimination between pABA and sulfonamides, more than 1000-fold loss in binding affinity of sulfas to Sul enzymes, and robust pan-sulfonamide resistance. We detect no fitness cost due to this active site modification, as it does not compromise the rate of dihydropteroate biosynthesis and complements the thymidine-auxotrophy of an E. coli folP deletion strain. Lab-evolved sulfa-resistance folP recapitulated this mechanism through the same active site insertion. Finally, we show that this insertion and a nearby loop confer increased active site flexibility of Sul enzymes relative to DHPS. These results provide a molecular foundation for revisiting DHPS-targeted antibacterials to evade resistance.

In Silico Analysis of Chalcone Derivatives as Potential Antibacterial Agents against DHPS Enzyme

“…ntimicrobial resistant (AMR) is a condition in which antimicrobials including antibacterial, antiviral, antifungal, etc are no longer effective in curing infection and diseases. It poses a serious threat as it is estimated to cause more than 1 million deaths and more than 4 million infectionrelated diseases in 2019 [1], [2]. This issue becomes one of United Nation concerns as it relates to the Sustainable Development Goals (SDGs) on health problem which leads to point 4, good health and well-being.…”

“…The further transformation will generate tetrahydrofolate for DNA and RNA synthesis. DHPS has two cleft for its substrates, pABA and DHPP [1], [3]- [5]. Thus, some inhibitors could mimic the structure of the substrates and act as competitive inhibitor.…”

Emergence of the fourth mobile sulfonamide resistance gene sul4 in clinical Salmonella enterica

“…Given their extensive utilization, sulfonamide-subsisting bacteria were identified in 2008 for the first time (Dantas et al, 2008), and then many species of bacteria showing sulfonamides resistant were discovered (Deng et al, 2018;Ma et al, 2022). Currently, the most common mechanism of sulfonamide resistance in the majority of bacteria was plasmid-borne, highly mobilized sul1, sul2, and sul3, which encode dihydropteroate synthase (Wang et al, 2014;Nunes et al, 2020;Tang et al, 2022a;Venkatesan et al, 2023). In 2017, the fourth mobile sulfonamide resistance gene sul4 was identified in river sediment with amplicon metagenomic sequencing for the first time (Razavi et al, 2017).…”