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Aggregation state of spin-labeled cecropin AD in solution
H S Mchaourab1, J S Hyde, J B Feix
1Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226.
Biochemistry
|November 9, 1993
Summary
Spin-labeled cecropin AD peptide is monomeric in water but aggregates in 5-10% hexafluoro-2-propanol (HFP). This aggregation, studied via ESR, may explain how cecropins form channels in membranes.
Area of Science:
- Biophysics
- Structural Biology
- Membrane Proteins
Background:
- Cecropins are antimicrobial peptides with channel-forming capabilities.
- Understanding their aggregation is key to elucidating their membrane interaction mechanism.
Purpose of the Study:
- To investigate the aggregation state of a spin-labeled cecropin AD peptide.
- To explore the structural transitions induced by hexafluoro-2-propanol (HFP).
Main Methods:
- Synthesis of a spin-labeled cecropin AD derivative.
- Electron spin resonance (ESR) spectroscopy to analyze peptide conformation and aggregation.
- Varying concentrations of HFP to induce structural changes.
Main Results:
- In aqueous solution, cecropin AD is monomeric and flexible (random coil).
- 5-10% HFP induces peptide aggregation, evidenced by restricted spin-label motion and ESR line broadening.
- Higher HFP concentrations lead to a folded monomeric state.
Conclusions:
- Cecropin AD undergoes aggregation in a specific HFP concentration range (5-10%).
- This aggregation involves two distinct structural transitions.
- Observed aggregation may be relevant to cecropin-mediated membrane channel formation.