Oriented Circular Dichroism: A Method to Characterize Membrane-Active Peptides in Oriented Lipid Bilayers

• DOI: 10.1021/acs.accounts.5b00346
• Publication Date: 2016-01-12T20:41:19Z
• Authors: Jochen Bürck; Parvesh Wadhwani; Susanne Fanghänel; Anne S. Ulrich
• Keywords: Helix (gastropod)

ConspectusThe structures of membrane-bound polypeptides are intimately related to their functions and may change dramatically with the lipid environment. Circular dichroism (CD) is a rapid analytical method that requires relatively low amounts material no labeling. Conventional CD routinely used monitor secondary structure peptides proteins in solution, for example, presence ligands other binding partners. In case membrane-active transmembrane proteins, these measurements can be applied to, remain limited samples containing detergent micelles or small sonicated vesicles. Such traditional analysis reveals only structures. With help an oriented circular (OCD) setup, however, based on preparation macroscopically bilayers, it possible address membrane alignment peptide addition its conformation. This approach has been mostly α-helical so far, but structural elements conceivable as well. OCD relies Moffitt's theory, which predicts electronic transition dipole moments backbone amide bonds helical polarized either parallel perpendicular helix axis. The interaction electric field vector circularly light transitions results spectrum peptide, exhibits characteristic line shape reflects angle between axis bilayer normal. For respect surface (S-state), corresponding "fingerprint" band around 208 nm will exhibit maximum negative amplitude. If changes via obliquely tilted (T-state) fully inserted orientation (I-state), ellipticity at decreases value approaches zero due decreased interactions dipole.Compared conventional CD, data not collected biologically relevant environment highly hydrated planar (whose composition varied will), provides information about tilt polypeptide membrane. It choice screening numerous different conditions, such concentration, composition, additives, pH, temperature, sample hydration. All factors have found affect membrane, while having little influence many cases, observed realignment could biological action, pore formation by antimicrobial cell-penetrating peptides, events segments integral proteins. Likewise, any lipid-induced conversion from α-helix β-sheeted conformation readily picked up interpreted terms protein instability amyloid-formation.