Abstract:
DNA ligases are important enzymes which catalyze
the joining of nicks between adjacent bases of
double-stranded DNA. NAD1-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 NAD1 binding domain of the
Mycobacterium tuberculosis LigA, we have identified
N1, Nn-bis-(5-deoxy-a-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 NAD1 for binding and
inhibit enzyme activity with IC50 values in the mM
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 NAD1 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 ATPdependent
ligase. This class of inhibitors holds
out the promise of rational development of new
anti-tubercular agents.
