Structural reconstruction of protein ancestry

Area of Science:

• Structural Biology
• Evolutionary Biology
• Immunology

Background:

• Ancestral protein reconstruction typically relies on computational analysis of modern protein sequences.
• Highly divergent protein families, like jawed vertebrate antigen receptors (B-cell and T-cell receptors), pose challenges for sequence-based reconstruction.
• The evolutionary origin of antigen receptors from an extinct homodimeric ancestor lacks direct molecular evidence.

Purpose of the Study:

• To reconstruct and characterize ancient homodimeric receptors, overcoming limitations of sequence-based methods.
• To provide molecular evidence for the evolutionary theories of antigen receptor diversification.
• To investigate the structural basis of antigen binding in reconstructed ancestral molecules.

Main Methods:

• Employed a structural approach combined with laboratory evolution to reconstruct ancestral protein molecules.
• Determined high-resolution crystal structures of reconstructed homodimeric receptors.
• Characterized the interaction of reconstructed receptors with hen-egg white lysozyme (antigen).

Main Results:

• Successfully reconstructed homodimeric receptors capable of nanomolar affinity binding to asymmetrical antigen.
• Crystal structures revealed selective recruitment and structural plasticity within the receptor-binding site enabling antigen interaction.
• Provided the first structural evidence supporting theories on the evolution of antigen receptors.

Conclusions:

• The study offers a novel structural approach for reconstructing ancient proteins, particularly useful for highly divergent families.
• Demonstrated how ancestral receptor structures facilitate specific antigen binding through adaptable binding sites.
• Presents a blueprint for experimental reconstruction of protein ancestry, even without phylogenetic data.