Highly homologous proteins exert opposite biological activities by using different interaction interfaces

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Biology

Background:

• The ASPP protein family plays crucial roles in regulating apoptosis.
• ASPP2 and iASPP, highly homologous proteins, exhibit opposing functions in apoptosis.
• Autoinhibitory interactions between Ank-SH3 and Pro domains regulate ASPP protein activity.

Purpose of the Study:

• To elucidate the molecular basis for the opposing roles of ASPP2 and iASPP in apoptosis.
• To investigate the differences in the Pro-Ank-SH3 interaction between iASPP and ASPP2.
• To understand how fine-tuning of interaction interfaces leads to differential biological activities.

Main Methods:

• Detailed biophysical and molecular studies.
• Comparative analysis of Pro-Ank-SH3 interactions in iASPP and ASPP2.

Main Results:

• The iASPP Pro domain is disordered.
• iASPP Ank-SH3 interacts with iASPP Pro via the fourth Ank repeat and RT loop.
• ASPP2 Ank-SH3 interacts with ASPP2 Pro via the first Ank repeat and n-src loop.
• Identified distinct interaction sites within the homologous proteins' interfaces.

Conclusions:

• Differential binding interfaces in homologous proteins can lead to distinct biological functions.
• Fine-tuning of protein-protein interactions is a key mechanism for regulating apoptosis.
• The study provides a molecular explanation for the opposite activities of ASPP2 and iASPP.