Ex-527 inhibits Sirtuins by exploiting their unique NAD+-dependent deacetylation mechanism

Proc Natl Acad Sci U S A. 2013 Jul 23;110(30):E2772-81. doi: 10.1073/pnas.1303628110. Epub 2013 Jul 9.


Sirtuins are protein deacetylases regulating metabolism and stress responses. The seven human Sirtuins (Sirt1-7) are attractive drug targets, but Sirtuin inhibition mechanisms are mostly unidentified. We report the molecular mechanism of Sirtuin inhibition by 6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide (Ex-527). Inhibitor binding to potently inhibited Sirt1 and Thermotoga maritima Sir2 and to moderately inhibited Sirt3 requires NAD(+), alone or together with acetylpeptide. Crystal structures of several Sirtuin inhibitor complexes show that Ex-527 occupies the nicotinamide site and a neighboring pocket and contacts the ribose of NAD(+) or of the coproduct 2'-O-acetyl-ADP ribose. Complex structures with native alkylimidate and thio-analog support its catalytic relevance and show, together with biochemical assays, that only the coproduct complex is relevant for inhibition by Ex-527, which stabilizes the closed enzyme conformation preventing product release. Ex-527 inhibition thus exploits Sirtuin catalysis, and kinetic isoform differences explain its selectivity. Our results provide insights in Sirtuin catalysis and inhibition with important implications for drug development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylation
  • Carbazoles / chemistry
  • Carbazoles / pharmacology*
  • Models, Molecular
  • NAD / metabolism*
  • Sirtuins / antagonists & inhibitors*
  • Stereoisomerism


  • 6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide
  • Carbazoles
  • NAD
  • Sirtuins

Associated data

  • PDB/4BUZ
  • PDB/4BV2
  • PDB/4BV3
  • PDB/4BVB
  • PDB/4BVE
  • PDB/4BVF
  • PDB/4BVG
  • PDB/4BVH