9SVM

Structure of dihydrofolate reductase from Burkholderia thailandensis complexed with trimethoprim and dihydrofolate

Summary for 9SVM

• Entry DOI: 10.2210/pdb9svm/pdb
• Related: 9SVN
• Descriptor: Dihydrofolate reductase, TRIMETHOPRIM, NADPH DIHYDRO-NICOTINAMIDE-ADENINE-DINUCLEOTIDE PHOSPHATE, ... (5 entities in total)
• Functional Keywords: thymine synthesis tetrahydrofolate, oxidoreductase
• Biological source: Burkholderia thailandensis
• Total number of polymer chains: 1
• Total formula weight: 19909.93

Authors

Mechulam, Y.,Schmitt, E.,Lazennec-Schurdevin, C. (deposition date: 2025-10-03, release date: 2026-08-26)

Primary citation

Guillier, S.,Lazennec-Schurdevin, C.,Mondange, L.,Sarilar, V.,Marchandeau, M.,Lemoigne, C.,Lamer, O.,Lescat, M.,Schmitt, E.,Mechulam, Y.,Garrec, J.,Biot, F.
Evolutionary Convergence on a Dihydrofolate Reductase Mutation Drives Trimethoprim-Sulfamethoxazole Resistance in Burkholderia thailandensis.
Acs Infect Dis., 12:2627-2641, 2026

PubMed Abstract: Trimethoprim-sulfamethoxazole (SXT) remains central to melioidosis eradication therapy, yet the genetic basis of resistance evolution in Burkholderia pseudomallei is not fully defined. Using Burkholderia thailandensis as a biosafe surrogate, we subjected populations to stepwise in vitro evolution under increasing SXT concentrations. Whole-genome sequencing revealed rapid population diversification followed by selective sweeps leading to fixation of fitter resistant variants. Early adaptation involved mutations in regulators of RND efflux systems and folate-associated genes, consistent with multifactorial resistance. Despite this heterogeneity, all evolutionary trajectories converged on a single nonsynonymous substitution, I99L, in dihydrofolate reductase (DHFR/FolA), which rose to fixation at high SXT concentrations. This substitution mirrors changes reported in SXT-resistant B. pseudomallei isolates from chronic infections. Allelic reconstruction demonstrated that Bt-DHFR(I99L) is sufficient to confer a 4- to 16-fold increase in trimethoprim MIC. Biochemical and structural analyses showed preserved catalytic activity but reduced trimethoprim binding, consistent with an allosteric resistance mechanism. Together, these findings establish DHFR as a dominant evolutionary target under SXT pressure and support B. thailandensis as a robust model for dissecting resistance evolution in B. pseudomallei.

PubMed: 42599400
DOI: 10.1021/acsinfecdis.5c01132

Experimental method

X-RAY DIFFRACTION (1.84 Å)