X-ray structural analysis of compensating mutations at the barnase-barstar interface

Area of Science:

• Biochemistry
• Structural Biology
• Protein Engineering

Background:

• Barnase and barstar form a stable protein-protein complex essential for cellular regulation.
• A mutation in barnase (His-102 to Lysine) significantly weakens this interaction due to charge incompatibility.
• Understanding compensatory mechanisms is crucial for protein design and function studies.

Purpose of the Study:

• To determine the crystal structures of barstar mutants and their complexes with barnase variants.
• To elucidate the structural basis for compensation of the barnase-barstar interaction defect.
• To investigate the role of solvation and hydrogen bonding in restoring complex stability.

Main Methods:

• X-ray crystallography was used to determine the three-dimensional structures.
• Analysis of protein-protein interfaces and residue interactions.
• Comparison of wild-type and mutant complex structures.

Main Results:

• Crystal structures of barstar mutants (Y29P, Y29D/Y30W) and complexes with barnase (wild-type and H102K) were determined.
• Barstar mutants effectively compensate for the loss of interaction energy caused by the barnase H102K mutation.
• Structural analysis indicates charge solvation of Lys-102 and hydrogen bond formation contribute to compensation.

Conclusions:

• The determined structures provide insights into the molecular mechanisms of protein-protein interaction compensation.
• Solvation of charged residues and specific hydrogen bonds play critical roles in stabilizing the barnase-barstar complex.
• These findings have implications for engineering protein interactions and understanding enzyme inhibition.