Crystal structure of Bacillus anthracis dihydrofolate reductase with the dihydrophthalazine-based trimethoprim derivative RAB1 provides a structural explanation of potency and selectivity.
Bacillus anthracis possesses an innate resistance to the antibiotic trimethoprim due to poor binding to dihydrofolate reductase (DHFR); currently, there are no commercial antibacterials that target this enzyme in B. anthracis. We have previously reported a series of dihydrophthalazine-based trimethoprim derivatives that are inhibitors for this target. In the present work, we have synthesized one compound (RAB1) displaying favorable 50% inhibitory concentration (54 nM) and MIC (< or =12.8 microg/ml) values. RAB1 was cocrystallized with the B. anthracis DHFR in the space group P2(1)2(1)2(1), and X-ray diffraction data were collected to a 2.3-A resolution. Binding of RAB1 causes a conformational change of the side chain of Arg58 and Met37 to accommodate the dihydrophthalazine moiety. Unlike the natural substrate or trimethoprim, the dihydrophthalazine group provides a large hydrophobic anchor that embeds within the DHFR active site and accounts for its selective inhibitory activity against B. anthracis.
Department of Veterinary Pathobiology, Oklahoma State University, Stillwater, OK 74078, USA. christina.bourne@okstate.edu
Christina R
CR
Bourne
Richard A
RA
Bunce
Philip C
PC
Bourne
K Darrell
KD
Berlin
Esther W
EW
Barrow
William W
WW
Barrow
D001408:Bacillus anthracis / Q000187:drug effects / Q000201:enzymology*; D008958:Models, Molecular; D011485:Protein Binding; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014295:Trimethoprim / Q000031:analogs & derivatives / Q000737:chemistry*; D014961:X-Ray Diffraction
D014295:Trimethoprim; D013762:Tetrahydrofolate Dehydrogenase