Structural basis of IAP recognition by Smac/DIABLO

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Apoptosis is vital for metazoan development and homeostasis.
• Inhibitor-of-apoptosis (IAP) proteins regulate cell death by inhibiting caspases via BIR domains.
• Smac/DIABLO, a mitochondrial protein, promotes apoptosis by antagonizing IAPs.

Purpose of the Study:

• To elucidate the structural basis of Smac/DIABLO interaction with IAPs.
• To understand the role of Smac/DIABLO's N-terminus in apoptosis regulation.
• To provide insights into potential drug targets for modulating apoptosis.

Main Methods:

• High-resolution crystal structure determination of Smac/DIABLO complexed with XIAP BIR3 domain.
• Analysis of protein-protein interactions and binding interfaces.

Main Results:

• The crystal structure reveals Smac/DIABLO's N-terminal four residues (AVPI) bind to a surface groove on XIAP BIR3.
• The N-terminal alanine residue engages in hydrophobic interactions and hydrogen bonding within the BIR3 domain.
• This interaction explains the functional importance of Smac/DIABLO's N-terminus and conserved motifs in related proteins.

Conclusions:

• The N-terminus of Smac/DIABLO is critical for binding IAPs and relieving caspase inhibition.
• Structural insights explain Smac/DIABLO's mechanism in promoting apoptosis.
• Identified structural features offer potential for developing novel therapeutic agents targeting apoptosis pathways.