A domain-swapped RNase A dimer with implications for amyloid formation.

Area of Science:

• Protein biochemistry
• Structural biology
• Biophysics

Background:

• Bovine pancreatic ribonuclease A (RNase A) is a well-studied enzyme.
• RNase A can form dimers under specific conditions, such as mild acid concentration.
• Previous work identified a minor dimer formed via N-terminal alpha-helix swapping.

Purpose of the Study:

• To elucidate the structural mechanism of major bovine pancreatic ribonuclease A dimer formation.
• To investigate the implications of different domain swapping strategies in protein oligomerization.
• To propose a model for aggregate formation involving three-dimensional domain swapping.

Main Methods:

• Biochemical analysis of RNase A dimerization.
• Structural characterization of RNase A dimers.
• Comparative analysis of major and minor dimer formation pathways.

Main Results:

• Bovine pancreatic ribonuclease A forms two distinct dimers: a major and a minor component.
• The major dimer is formed through swapping of C-terminal beta-strands.
• This represents the first observed instance of three-dimensional (3D) domain swapping in different protein regions within the same protein.
• The hinge loop of the major dimer resembles a polar zipper, suggesting a mechanism for aggregate formation.

Conclusions:

• The major dimer of RNase A forms via C-terminal beta-strand swapping, a novel 3D domain swapping mechanism.
• This distinct swapping mechanism allows for the formation of tightly bonded higher-order oligomers.
• The identified polar zipper-like hinge loop provides a model for protein aggregate formation through 3D domain swapping.