Catalysis and Sulfa Drug Resistance in Dihydropteroate Synthase

Abstract

The sulfonamide antibiotics inhibit dihydropteroate synthase (DHPS), a key enzyme in the folate pathway of bacteria and primitive eukaryotes. However, resistance mutations have severely compromised the usefulness of these drugs. Here, we report structural, computational and mutagenesis studies on the catalytic and resistance mechanisms of DHPS. By performing the enzyme-catalyzed reaction in crystalline DHPS, we have structurally characterized key intermediates along the reaction pathway. Results support an SN1 reaction mechanism via formation of a novel cationic pterin intermediate. We also show that two conserved loops generate a substructure during catalysis that creates a specific binding pocket for p-aminobenzoic acid, one of the two DHPS substrates. This substructure, together with the pterin-binding pocket, explains the roles of the conserved active site residues, and reveals how sulfonamide resistance arises.

Synthesis, <i>in Vitro</i> and <i>in Silico</i> Studies of Some Novel 5-Nitrofuran-2-yl Hydrazones as Antimicrobial and Antitubercular Agents

“…45) Crystallographic data of Bacillus anthracis dihydropteroate synthase (BaDHPS) bound to sulfathiazole-6-hydroxymethyl-7,8-dihydropterin-pyrophosphate (STZ-DHPP) adduct was obtained from Protein Data Bank (PDB code 3TYE). 46) Similarly, data obtained from docking shows that 21f can interact with BaDHPS as STZ-DHPP with the same target. The benzene-sulfonamide moiety of 21f occupies virtually the same position observed in the STZ-DHPP-BaDHPS complex; thereby establishing the characteristic hydrogen bond between its sulfonamide moiety and the backbone NH group of Ser221, in addition to an extra hydrogen bond with Asn196 (Fig.…”

Design, synthesis, antimicrobial evaluation and molecular docking studies of some new 2,3-dihydrothiazoles and 4-thiazolidinones containing sulfisoxazole

“…For the purpose of this study, the crystal structure of DHPS from B. anthracis (BaDHPS) bound to the STZ-DHPP adduct 18 was retrieved from the Protein Data Bank (PDB code: 3TYE) and processed as described previously 24 . The studied compounds were docked into BaDHPS using the flexible Molecular Operating Environment (MOE) Dock methodology (Montreal, QC, Canada) 26 .…”

“…To the best of our knowledge, only two crystal structures of a sulfa-related drug bound to the active site of DHPS were solved and reported in the Protein Data Bank (PDB). The crystal structure of Bacillus anthracis dihydropteroate synthase (BaDHPS) bound to sulfathiazole-6-hydroxymethyl-7,8-dihydropterin-pyrophosphate (STZ-DHPP) adduct was reported by Yun et al 18 . In this structure, the STZ-DHPP adduct occupies both the PABA and pterin-binding pockets of DHPS ( Figure I, Supplementary data) 18 .…”

“…The crystal structure of Bacillus anthracis dihydropteroate synthase (BaDHPS) bound to sulfathiazole-6-hydroxymethyl-7,8-dihydropterin-pyrophosphate (STZ-DHPP) adduct was reported by Yun et al 18 . In this structure, the STZ-DHPP adduct occupies both the PABA and pterin-binding pockets of DHPS ( Figure I, Supplementary data) 18 . Trimethoprim, the dihydrofolate reductase inhibitor, is used in combination with sulfa drugs to increase the therapeutic efficacy 19 .…”

“…On the other hand, 2,3-dihydrothiazoles and 4-thiazolidinones have occupied a unique position in the design and synthesis of biologically active antimicrobial agents [20][21][22] . In this study, we used the reported STZ-DHPP adduct 18 as a lead compound to design potent antimicrobial agents targeting both the PABA and pterin-binding pockets of the DHPS enzyme, thereby inhibiting the biosynthesis of the dihydrofolic acid. The thiazole, methylene and pteridine moieties were replaced by the 3,4-dimethyl-isoxazole, carbonyl and substituted thiazole rings; respectively ( Figure 1).…”