A NMR STUDY OF SMAC MIMICS TARGETING BOTH THE BIR2 AND BIR3 DOMAINS IN XIAP PROTEIN.

XIAP is a central apoptosis regulator that inhibits apoptosis by binding to and inhibiting the effectors caspase-3/-7 and an initiator caspase-9 through its BIR2 and BIR3 domains, respectively. Smac protein in its dimeric form effectively antagonizes XIAP by concurrently targeting both its BIR2 and BIR3 domains1. Novel proapoptotic Smac mimics/XIAP inhibitors have been designed, synthesized and characterized in our group. These pseudopeptides, containing the 1-aza-2-oxobicyclo[4.3.0]nonane scaffold, were tested by tr-NOE and STD-NMR experiments2. Here, we show the binding evidence and the epitope mapping for a series of new compounds respect to different fragments of XIAP protein: the STD spectra of selected Smac- mimics suggest different binding interactions with BIR2 and BIR3 domains. So, we are able to design new higher affinity compounds.