Monitoring the Uniformity of Alpha Helices in Lipophilic Environments

It is known that membrane-embedded α-helices are more uniform structurally than their aqueous counterparts.  Despite this uniformity, protein dynamics are thought to be common in these proteins in order for them to conduct their cellular tasks.  However, how amino acid sequence facilitates these dynamics remains unknown, as methods for investigating structural heterogeneity in transmembrane proteins are limited.  Circular dichroism (CD) is often used to characterize the secondary structure of proteins, but its sensitivity to specific non-helical structural configurations is low.  Deep-ultraviolet resonance Raman spectroscopy (dUVRR) is a structurally sensitive spectroscopic technique emerging for analyzing membrane protein structure. Using a model leucine-alanine peptide in hydrated and dehydrated environments, changes in the amide and aromatic modes in dUVRR spectra were observed to determine the impact of structure due to environment.  A set of model leucine-alanine peptides containing aromatic and helix breaking residues (HBR) proline or glycine were designed to test their role in promoting helical instability in lipophilic environments.  The secondary structure of each peptide was monitored via dUVRR and CD spectroscopies.  Changes in the aromatic and amide modes indicate that introduction of hydration and HBRs promote “unwinding” of the helix.