Crystal structural analysis of protein-protein interactions drastically destabilized by a single mutation

Area of Science:

• Biochemistry
• Structural Biology
• Protein Interactions

Background:

• The barnase-barstar complex is a model system for studying protein-protein interactions.
• A specific mutation (barstar Asp39 to Ala) drastically destabilizes this complex, but the structural basis was unknown.

Purpose of the Study:

• To elucidate the structural mechanism behind the significant destabilization of the barnase-barstar complex caused by the barstar Asp39Ala mutation.

Main Methods:

• X-ray crystallography was used to determine the structure of the mutant barnase-barstar complex at 1.58 Å resolution.
• Molecular dynamics simulations were employed to analyze the dynamics of water molecules at the protein interface.

Main Results:

• The overall and interface structures of the mutant complex were similar to the wild-type.
• A significant difference was observed in the hydrogen bond network mediated by water molecules at the interface.
• The mutation led to the formation of a channel-like structure of water molecules penetrating the complex, increasing their mobility.

Conclusions:

• The drastic destabilization of the barnase-barstar interaction by the barstar Asp39Ala mutation is likely due to the formation of a unique channel-like water structure at the interface.
• This finding highlights the critical role of interfacial water networks in modulating protein-protein binding affinity.