1 research outputs found
Slow-Binding Inhibition of <i>Mycobacterium tuberculosis</i> Shikimate Kinase by Manzamine Alkaloids
Tuberculosis represents a significant
public health crisis. There
is an urgent need for novel molecular scaffolds against this pathogen.
We screened a small library of marine-derived compounds against shikimate
kinase from <i>Mycobacterium tuberculosis</i> (<i>Mt</i>SK), a promising target for antitubercular drug development. Six
manzamines previously shown to be active against <i>M. tuberculosis</i> were characterized as <i>Mt</i>SK inhibitors: manzamine
A (<b>1</b>), 8-hydroxymanzamine A (<b>2</b>), manzamine
E (<b>3</b>), manzamine F (<b>4</b>), 6-deoxymanzamine
X (<b>5</b>), and 6-cyclohexamidomanzamine A (<b>6</b>). All six showed mixed noncompetitive inhibition of <i>Mt</i>SK. The lowest <i>K</i><sub>I</sub> values were obtained
for <b>6</b> across all <i>Mt</i>SKāsubstrate
complexes. Time-dependent analyses revealed two-step, slow-binding
inhibition. The behavior of <b>1</b> was typical; initial formation
of an enzymeāinhibitor complex (EI) obeyed an apparent <i>K</i><sub>I</sub> of ā¼30 Ī¼M with forward (<i>k</i><sub>5</sub>) and reverse (<i>k</i><sub>6</sub>) rate constants for isomerization to an EI* complex of 0.18 and
0.08 min<sup>ā1</sup>, respectively. In contrast, <b>6</b> showed a lower <i>K</i><sub>I</sub> for the initial encounter
complex (ā¼1.5 Ī¼M), substantially faster isomerization
to EI* (<i>k</i><sub>5</sub> = 0.91 min<sup>ā1</sup>), and slower back conversion of EI* to EI (<i>k</i><sub>6</sub> = 0.04 min<sup>ā1</sup>). Thus, the overall inhibition
constants, <i>K</i><sub>I</sub>*, for <b>1</b> and <b>6</b> were 10 and 0.06 Ī¼M, respectively. These findings
were consistent with docking predictions of a favorable binding mode
and a second, less tightly bound pose for <b>6</b> at <i>Mt</i>SK. Our results suggest that manzamines, in particular <b>6</b>, constitute a new scaffold from which drug candidates with
novel mechanisms of action could be designed for the treatment of
tuberculosis by targeting <i>Mt</i>SK