The ASPP interaction network: electrostatic differentiation between pro- and anti-apoptotic proteins.

Area of Science:

• Molecular Biology
• Cell Biology
• Structural Biology

Background:

• The ASPP protein family comprises apoptosis regulators with opposing functions: ASPP1 and ASPP2 promote apoptosis, while iASPP inhibits it.
• The underlying molecular mechanisms driving these divergent functional outcomes remain largely unknown.
• The C-terminal ankyrin repeats and SH3 domain (ANK-SH3) are crucial for ASPP interactions with key apoptosis regulators like p53, Bcl-2, and NFκB.

Purpose of the Study:

• To elucidate the structural basis for the functional diversity within the ASPP protein family.
• To compare ASPP interactions at the protein interface level, examining both ASPP2(ANK-SH3) with different partners and various ASPP family members with specific partners.

Main Methods:

• Comparative analysis of protein-protein interaction interfaces.
• Structural characterization of ASPP2(ANK-SH3) complexes with p53, Bcl-2, and NFκB.
• Analysis of electrostatic surface properties and residue composition at binding interfaces.

Main Results:

• ASPP2(ANK-SH3) utilizes distinct but spatially proximate binding sites on the same face for p53, Bcl-2, and NFκB.
• An intramolecular interaction site within ASPP2 overlaps with its intermolecular binding sites.
• ASPP1 and ASPP2 exhibit greater negative charge at key contact residues compared to iASPP, facilitating interactions with positively charged partners like p53CD, Bcl-2, and NFκB.

Conclusions:

• Electrostatic differences in the binding interfaces of ASPP proteins are a key determinant of their opposing roles in apoptosis regulation.
• A gain of positive charge on the non-binding face of ASPP1/2 may contribute to orienting the protein towards its negatively charged binding face.