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Antimicrobial Agents and Chemotherapy, May 2001, p. 1407-1416, Vol. 45, No. 5
Department of Microbiology, Colorado State
University, Fort Collins, Colorado 805231;
College of Pharmacy, University of Illinois at Chicago,
Chicago, Illinois 606122; and Department
of Biology, Washington University, St. Louis, Missouri
631303
Received 14 August 2000/Returned for modification 3 October
2000/Accepted 12 February 2001
An L-rhamnosyl residue plays an essential structural
role in the cell wall of Mycobacterium tuberculosis.
Therefore, the four enzymes (RmlA to RmlD) that form dTDP-rhamnose from
dTTP and glucose-1-phosphate are important targets for the development
of new tuberculosis therapeutics. M. tuberculosis genes
encoding RmlA, RmlC, and RmlD have been identified and expressed in
Escherichia coli. It is shown here that genes for only
one isotype each of RmlA to RmlD are present in the M.
tuberculosis genome. The gene for RmlB is Rv3464. Rv3264c was
shown to encode ManB, not a second isotype of RmlA. Using recombinant
RmlB, -C, and -D enzymes, a microtiter plate assay was developed to
screen for inhibitors of the formation of dTDP-rhamnose. The three
enzymes were incubated with dTDP-glucose and NADPH to form
dTDP-rhamnose and NADP+ with a concomitant decrease in
optical density at 340 nm (OD340). Inhibitor candidates
were monitored for their ability to lower the rate of OD340
change. To test the robustness and practicality of the assay, a
chemical library of 8,000 compounds was screened. Eleven inhibitors
active at 10 µM were identified; four of these showed activities
against whole M. tuberculosis cells, with MICs from 128 to 16 µg/ml. A rhodanine structural motif was present in three of the
enzyme inhibitors, and two of these showed activity against whole
M. tuberculosis cells. The enzyme assay was used to
screen 60 Peruvian plant extracts known to inhibit the growth of
M. tuberculosis in culture; two extracts were active
inhibitors in the enzyme assay at concentrations of less than 2 µg/ml.
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.5.1407-1416.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Drug Targeting Mycobacterium
tuberculosis Cell Wall Synthesis: Genetics of dTDP-Rhamnose
Synthetic Enzymes and Development of a Microtiter Plate-Based
Screen for Inhibitors of Conversion of dTDP-Glucose to
dTDP-Rhamnose
*
Corresponding author. Mailing address: Department of
Microbiology, Colorado State University, Fort Collins, CO 80523. Phone: (970) 491-1784. Fax: (970) 491-1815. E-mail:
mmcneil{at}cvmbs.colostate.edu.
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