Peptides targeting caspase inhibitors.
Here we report on the identification of peptides targeting the X-inhibitor of apoptosis protein (XIAP). XIAP functions as a caspase inhibitor and is a member of the inhibitors of apoptosis (IAP) family of proteins. IAPs are often overexpressed in cancers and leukemias and are associated with an unfavorable clinical prognosis. We have selected peptides from a phage library by using recombinant full-length human XIAP or a fragment containing only the baculovirus IAP repeat 2 (BIR2) domain. A consensus motif, C(D/E/P)(W/F/Y)-acid/basic-XC, was recovered from two independent screenings by using different libraries. Phage-displaying variations of the consensus sequence bound specifically to the BIR2 domain of XIAP but not to other IAPs. The interaction was specific as it could be blocked by the cognate synthetic peptides in a dose-dependent manner. Phage displaying the XIAP-binding motif CEFESC bound to the BIR2 domain of XIAP with an estimated dissociation constant of 1.8 nm as determined by surface plasmon resonance. Protein-protein interaction assays revealed that caspase-3 and caspase-7 (but not caspase-8) blocked the binding of the CEFESC phage to XIAP, indicating that this peptide targets a domain within XIAP that is related to the caspase-binding site. In fact, the sequence EFES is homologous to a loop unique to the executioner caspase-3 and caspase-7 that are targeted by XIAP. Finally, we demonstrated that an internalizing version of the XIAP-binding peptide identified in our screenings (PFKQ) can induce programmed cell death in leukemia cells. Peptides interacting with XIAP could serve as prototypes for the design of low molecular weight modulators of apoptosis.
Tamm
Ingo
I
The Burnham Institute, La Jolla, California 97037, USA.
Trepel
Martin
M
Cardó-Vila
Marina
M
Sun
Yan
Y
Welsh
Kate
K
Cabezas
Edelmira
E
Swatterthwait
Arnold
A
Arap
Wadih
W
Reed
John C
JC
Pasqualini
Renata
R
D020816:Amino Acid Motifs; D017209:Apoptosis; D001665:Binding Sites; D053148:Caspase 3; D053179:Caspase 7; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism / Q000494:pharmacology; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008024:Ligands; D010452:Peptide Biosynthesis; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry / Q000502:physiology*; D020349:Surface Plasmon Resonance; D013997:Time Factors; D051636:X-Linked Inhibitor of Apoptosis Protein
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D008024:Ligands; D019151:Peptide Library; D010455:Peptides; D011506:Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; C505407:CASP3 protein, human; C505520:CASP7 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053179:Caspase 7; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases