Structural basis of negative cooperativity in transthyretin

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biophysics

Background:

• Transthyretin (TTR) is a transport protein implicated in various diseases.
• Understanding TTR's ligand-binding mechanism is crucial for therapeutic development.
• Structural dynamics of TTR's binding sites are not fully elucidated.

Purpose of the Study:

• To compare the AC and BD binding sites of transthyretin (TTR).
• To investigate the structural changes in TTR upon ligand binding.
• To elucidate the mechanism behind negative cooperativity (NC) in TTR.

Main Methods:

• Analysis of interatomic distances between Ca atoms of equivalent amino acids across the tetramer channel.
• Comparison of channel diameters in apo TTR and TTR-ligand complexes.
• Development of a model for ligand-induced structural changes.

Main Results:

• Significant differences in beta-strand distances ('wave' character) observed between AC and BD sites in apo TTR.
• Ligand binding induces site collapse and conformational changes, affecting the second binding site.
• Observed structural changes correlate with the negative cooperativity (NC) effect.

Conclusions:

• TTR binding sites display inherent asymmetric structural dynamics.
• A sequential, cooperative binding model explains the observed negative cooperativity.
• These findings provide insights into TTR's allosteric regulation and ligand interactions.