A hybrid sequence approach to the paracelsus challenge

Area of Science:

• Protein engineering
• Structural biology
• Biophysics

Background:

• The Paracelsus Challenge aims to design proteins with novel folds.
• Understanding protein folding principles is crucial for designing new protein structures.
• Hybrid protein design offers a strategy to create proteins with desired structural properties.

Purpose of the Study:

• To design a protein sequence that deviates from its parent's helical structure and adopts a beta-sheet fold.
• To investigate the folding behavior and stability of a hybrid protein sequence.
• To explore the potential of incorporating a zinc-binding site for structure stabilization.

Main Methods:

• Constructed a hybrid protein sequence (Crotein-G) based on 434 Cro (helical) and protein G B1 domain (beta-sheet).
• Created a zinc-binding variant (ZCrotein-G) with a potential His3Cys1 site.
• Utilized circular dichroism spectroscopy to analyze protein secondary structure in the presence of 2,2,2-trifluoroethanol (TFE).

Main Results:

• Circular dichroism spectra indicated a shift towards beta-sheet structure in low concentrations with TFE.
• The designed proteins did not exhibit cooperative denaturation.
• Protein aggregation occurred at moderate concentrations or without TFE, and zinc addition did not stabilize ZCrotein-G.

Conclusions:

• The engineered Crotein-G sequence, while sharing identity with target and parent proteins, did not achieve a stable, native beta-sheet fold.
• Protein folding is complex, and sequence identity alone does not guarantee a specific structure.
• Further strategies are needed to overcome aggregation and achieve cooperative folding in designed proteins.