Interactions of SIRT1 with Acetyl Substrate,NAD~+ or Nicotinamide

SIRT1 is a NAD+-dependent protein deacetylase.Nicotinamide is a reaction product of the SIRT1-catalyzed deacetylation and also a noncompetitive inhibitor of SIRT1.Here we built the complex structures ofSIRT1/NAD+/p53acetyl peptideandSIRT1/ADPR/nicotinamideby protein homology modeling and molecular docking.According to the docking results,S265 and N346 of SIRT1 are involved in the interactions with NAD+,while S275is at the entrance of the NAD+binding pocket.Consistently,our enzyme kinetics studies proved that mutations of S265,S275 or N346either reduced or destroyed the interaction of NAD+with SIRT1.In addition,the carboxamide group of nicotinamide forms hydrogen bonds with I347 and D348,while the pyridine ring is buried in a hydrophobic environment surrounded by A262,I270,F273,I316 and I347.Interestingly,mutation of I316 to alanine increased the affinity of nicotinamide and dramatically improved its inhibitory activity,indicating that nicotinamide binds in the C pocket of SIRT1.