Transition states. Trapping a transition state in a computationally designed protein bottle

Area of Science:

• Biochemistry
• Structural Biology
• Computational Biology

Background:

• Determining the 3D structures of transition states (TSs) in chemical reactions is challenging due to their extremely short lifetimes.
• Diffraction methods like X-ray crystallography typically require stable structures for analysis.

Purpose of the Study:

• To stabilize a specific transition state conformation for direct structural determination.
• To overcome the inherent instability of transition states for crystallographic analysis.

Main Methods:

• Utilized computational protein design software (Rosetta) to engineer a binding pocket within a protein.
• Designed the pocket to stabilize the planar transition state conformation of biphenyl rotation via van der Waals interactions.
• Introduced a noncanonical amino acid, p-biphenylalanine, into the protein to present the biphenyl moiety.

Main Results:

• Successfully stabilized the planar, energetically disfavored transition state conformation of the biphenyl central carbon-carbon bond.
• Achieved direct observation of this stabilized transition state structure using X-ray crystallography.
• Demonstrated the trapping of the p-biphenylalanine side chain in the coplanar TS conformation within the designed protein.

Conclusions:

• Protein engineering can be used to stabilize and crystallize fleeting transition states.
• This approach provides a novel method for directly visualizing reaction intermediates.
• Opens new avenues for understanding reaction mechanisms at a structural level.