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Structure-function relationships in an antifreeze polypeptide. The effect of added bulky groups on activity
1Department of Chemistry, Boston University, Massachusetts 02215.
The Journal of Biological Chemistry
|August 5, 1993
Summary
Antifreeze polypeptides (AFPs) gain activity from side-by-side molecule interactions on ice. Specific bulky group placement, not overall hydrophobicity, is crucial for AFP function and ice binding.
Area of Science:
- Biochemistry
- Protein Science
- Biophysics
Background:
- Antifreeze activity in polypeptides (AFPs) is proposed to involve hydrophobic interactions between bound molecules on ice surfaces.
- Understanding the role of the helix's outward-facing surface is key to elucidating AFP function.
Purpose of the Study:
- To test the hypothesis that side-by-side hydrophobic interactions of antifreeze polypeptides (AFPs) on ice surfaces contribute to antifreeze activity.
- To assess the importance of the hydrophobic surface on non-ice-binding portions of the alpha-helical AFP.
Main Methods:
- Synthesis of AFP analogs with alanine replacements (Ala-->Gln or Ala-->Leu).
- Determination of antifreeze activity and helix stability of synthesized analogs.
- Molecular modeling studies to investigate structural effects of substitutions.
Main Results:
- Glutamine (Gln) replacements caused minor helix destabilization and reduced antifreeze activity but were generally tolerated.
- Bulk hydrophobicity of non-ice-binding faces did not appear to be a major determinant of AFP activity.
- Replacing residues at position 17 with Gln or Leucine abolished antifreeze activity, indicating location-specific effects.
Conclusions:
- The specific positioning of bulky groups, rather than overall surface hydrophobicity, is critical for AFP activity.
- Steric hindrance at specific sites (position 17) prevents effective AFP molecule association on ice surfaces, supporting the hydrophobic interaction hypothesis.