A dissection of specific and non-specific protein-protein interfaces

Area of Science:

• Structural Biology
• Biochemistry
• Computational Biology

Background:

• Protein-protein interactions (PPIs) are crucial for biological processes.
• Distinguishing specific from non-specific PPIs is essential for understanding protein function.
• Crystal packing can create interfaces mimicking specific interactions.

Purpose of the Study:

• To compare geometric and physicochemical properties of specific and non-specific PPI interfaces.
• To develop computational methods for identifying specific PPIs in crystal structures.

Main Methods:

• Analysis of crystal structures from the Protein Data Bank (PDB).
• Comparison of interface properties (size, symmetry, composition, hydrophobicity, atomic packing) between specific and non-specific interactions.
• Development of residue propensity and hydrophobic interaction scores.
• Evaluation of atomic packing compactness.

Main Results:

• Non-specific crystal packing interfaces resemble protein solvent-accessible surfaces.
• Non-specific interfaces are less hydrophobic and have fewer buried atoms than specific interfaces.
• Atomic packing is less compact in non-specific interfaces.
• A combination of interface area and buried atom fraction correctly identified quaternary structure in 88% of homodimers and 77% of monomers.
• Including residue propensity scores improved accuracy to 93-95%.

Conclusions:

• Geometric and physicochemical properties effectively differentiate specific and non-specific protein interfaces.
• Computational scoring methods can accurately predict protein quaternary structure from crystal structures.
• These findings aid in distinguishing biologically relevant interactions from crystal artifacts.