# DBT JRF 2020 — Question 142

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Medium

## Question

Which interactions are generally observed at the core of stable protein-protein complexes?

## Options

- **A.** salt bridges
- **B.** hydrogen bonds
- **C.** hydrophobic
- **D.** disulfide bonds

## Answer

Option C

## Explanation

Protein-protein interaction (PPI) interfaces: At the CORE of stable PPI interfaces, the dominant stabilising force is HYDROPHOBIC interactions. Key evidence: (1) Interface cores (central buried regions) are enriched in hydrophobic residues (Leu, Ile, Val, Phe, Trp, Met); (2) These residues bury their hydrophobic surfaces away from solvent — the hydrophobic effect drives complex formation (entropy gain from releasing ordered water molecules from non-polar surfaces); (3) Alanine-scanning mutagenesis reveals that core interface residues (hot spots) are predominantly hydrophobic. The periphery of PPI interfaces has more polar/charged residues forming H-bonds and salt bridges, but these are weaker and more variable. Disulfide bonds at PPI interfaces are limited to specific extracellular proteins. Carbonylation is a protein damage marker, not a PPI stabiliser.

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