Multistep mutational transformation of a protein fold through structural intermediates

Area of Science:

• Protein structure and evolution
• Biochemistry
• Structural biology

Background:

• Protein folds can undergo metamorphic evolution, involving significant structural changes.
• Understanding the evolutionary pathways of protein folds is crucial for deciphering protein structure-function relationships.

Purpose of the Study:

• To design and characterize hybrid proteins that mimic potential evolutionary intermediates between distinct protein folds.
• To investigate how sequence modifications influence protein folding and structural transitions.

Main Methods:

• Designed two homologous protein hybrids (XPH1, XPH2) based on Xfaso 1 (all-α) and Pfl 6 (α + β) Cro protein sequences.
• Determined the solution nuclear magnetic resonance (NMR) structures of XPH1 and XPH2.
• Analyzed structural similarity and differences using TM-align scores, DALI Z-scores, and backbone root mean square deviation (RMSD).

Main Results:

• XPH1 and XPH2 retained folds generally similar to their respective parents (Xfaso 1 and Pfl 6).
• Significant structural deviations were observed, particularly in secondary structure content, with hybrids exhibiting intermediate characteristics.
• The designed sequence progression demonstrated both abrupt and gradual changes in protein folding patterns.

Conclusions:

• Protein folds exhibit plasticity, allowing for polymetamorphic evolution through intermediate structures.
• Designed hybrid proteins can serve as models for studying evolutionary transitions in protein structure.
• The study provides insights into the mechanisms underlying protein fold diversification.