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.
Bourne
Christina R
CR
Department of Veterinary Pathobiology, Oklahoma State University, Stillwater, OK 74078, USA. christina.bourne@okstate.edu
Bunce
Richard A
RA
Bourne
Philip C
PC
Berlin
K Darrell
KD
Barrow
Esther W
EW
Barrow
William W
WW
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