Effects of Fluidity on the Ensemble Structure of a Membrane Embedded α-Helical Peptide

Melittin, the main hemolytic component of honeybee venom, is unfolded in an aqueous environment and folds into an alpha-helical conformation in a lipid environment. Membrane fluidity is known to affect the activity and structure of melittin. By combining two structurally sensitive optical methods, circular dichroism (CD) and deep-ultraviolet resonance Raman spectroscopy (dUVRR), we have identified distinct structural fluctuations in melittin correlated with increased and decreased 1,2-dimyristoylsn-glycero-3-phosphocholine bilayer fluidities. CD spectra have reduced intensity at temperatures above 22 degrees C and high concentrations of the cholesterol analog 5-alpha-cholestan-3 beta-ol indicating distortions in the a-helical structure under these conditions. No increase in the amide S is observed in the temperature-dependent dUVRR spectra, suggesting an increase in 3(10)-helical structure with increasing temperatures above 22 degrees C. However, incorporation of 25 mol% 5 alpha-cholestan-3 beta-ol resulted in a small increase in the amide S intensity indicating partial unfolding of melittin. (C) 2014 Wiley Periodicals, Inc.