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New ice-binding face for type I antifreeze protein.
J Baardsnes1, L H Kondejewski, R S Hodges
1Department of Biochemistry and the Protein Engineering Network of Centres of Excellence, Queen's University, Kingston, Ont., Canada.
FEBS Letters
|December 22, 1999
Summary
Type I antifreeze proteins (AFPs) from winter flounder bind ice using a newly identified alanine-rich face. This discovery challenges previous models of AFP-ice interactions.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Science
Background:
- Type I antifreeze protein (AFP) from winter flounder is a small, alanine-rich alpha-helix.
- It contains conserved Thr, Asx, and Leu residues thought to interact with ice.
- Recent studies question the role of Leu and Asn in ice-binding.
Purpose of the Study:
- To investigate the role of conserved alanine residues in Type I AFP ice-binding.
- To identify a new ice-binding face for Type I AFP.
Main Methods:
- Sequence alignment of five Type I AFP isoforms.
- Site-directed mutagenesis of alanine residues to leucine.
- Analysis of antifreeze activity and ice-binding interactions of mutant peptides.
Main Results:
- Alanine residues adjacent to the Thr-rich face are highly conserved.
- Mutations A19L and A20L retained wild-type antifreeze activity.
- Mutation A17L abolished antifreeze activity, while A21L showed reduced activity and weak ice interaction.
Conclusions:
- A novel ice-binding face for Type I AFP is proposed, involving conserved alanine residues.
- This face is located at right angles to the previously assumed Leu/Asn-rich face.
- Conserved alanines and adjacent threonine residues are crucial for effective ice binding.