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Elimination of a misfolded folding intermediate by a single point mutation
Jesper E Mogensen1, Henrik Ipsen, Jens Holm
1Department of Life Sciences, Aalborg University, Denmark.
Biochemistry
|March 24, 2004
Summary
Bet v 1 protein folding involves a misfolded intermediate, not caused by its water channel. A specific mutation (Tyr120) eliminates this intermediate, suggesting Tyr120 acts as a folding gatekeeper.
Area of Science:
- Protein folding dynamics
- Allergen structure-function relationships
- Biophysical characterization
Background:
- Bet v 1, a major birch pollen allergen, possesses a unique structure with a water-filled channel and hydrophobic shell.
- Protein folding pathways can involve transient intermediate states, which may be misfolded.
- Structural homologues like Mal d 1 may exhibit different folding mechanisms.
Purpose of the Study:
- To analyze the folding behavior of the Bet v 1 protein.
- To investigate the role of the water-filled channel and specific residues in Bet v 1 folding.
- To compare the folding mechanisms of Bet v 1 and its homologue Mal d 1.
Main Methods:
- Denaturation/refolding experiments using urea, pH, and SDS.
- Site-directed mutagenesis (Tyr120Trp).
- Analysis of folding intermediates and transition state structures.
Main Results:
- Bet v 1 populates a transient, misfolded intermediate during folding.
- The water-filled channel is not responsible for the misfolded intermediate.
- Mutation Tyr120Trp eliminates the intermediate, implicating Tyr120 as a folding regulator.
- Mal d 1 folds without detectable intermediates, with a significantly different transition state structure.
Conclusions:
- Bet v 1 folding is regulated by specific residues like Tyr120, which can act as gatekeepers.
- Structural homology does not guarantee similar folding mechanisms.
- Differences in local helix propensities may contribute to distinct folding pathways in homologous proteins.