Published online 15 December 2005
Article |
Mycobacterium tuberculosis NAD+-dependent DNA ligase is selectively inhibited by glycosylamines compared with human DNA ligase I
Molecular and Structural Biology Division, Central Drug Research Institute PO Box 173, Chattar Manzil, Mahatma Gandhi Marg, Lucknow 226001, India 1Medicinal and Process Chemistry Division, Central Drug Research Institute PO Box 173, Chattar Manzil, Mahatma Gandhi Marg, Lucknow 226001, India
*To whom correspondence should be addressed. Tel: +91 522 2612411, ext. 4442; Fax: +91 522 2623405; Email: ravi_anitha{at}yahoo.com
Received September 30, 2005. Revised October 28, 2005. Accepted November 22, 2005.
DNA ligases are important enzymes which catalyze the joining of nicks between adjacent bases of double-stranded DNA. NAD+-dependent DNA ligases (LigA) are essential in bacteria and are absent in humans. They have therefore been identified as novel, validated and attractive drug targets. Using virtual screening against an in-house database of compounds and our recently determined crystal structure of the NAD+ binding domain of the Mycobacterium tuberculosis LigA, we have identified N1, Nn-bis-(5-deoxy-
-D-xylofuranosylated) diamines as a novel class of inhibitors for this enzyme. Assays involving M.tuberculosis LigA, T4 ligase and human DNA ligase I show that these compounds specifically inhibit LigA from M.tuberculosis. In vitro kinetic and inhibition assays demonstrate that the compounds compete with NAD+ for binding and inhibit enzyme activity with IC50 values in the µM range. Docking studies rationalize the observed specificities and show that among several glycofuranosylated diamines, bis xylofuranosylated diamines with aminoalkyl and 1, 3-phenylene carbamoyl spacers mimic the binding modes of NAD+ with the enzyme. Assays involving LigA-deficient bacterial strains show that in vivo inhibition of ligase by the compounds causes the observed antibacterial activities. They also demonstrate that the compounds exhibit in vivo specificity for LigA over ATP-dependent ligase. This class of inhibitors holds out the promise of rational development of new anti-tubercular agents.
Correspondence may also be addressed to Rama Pati Tripathi. Tel: +91 522 2612411, ext. 4462; Fax: +91 522 2623405; Email: rpt_56{at}yahoo.com
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