To distinguish between the local secondary structures of an α-helix and a 310-helix, a biophysical technique called Electron Spin Echo Envelope Modulation (ESEEM) was developed. Previously, ESEEM, along with Site-Directed Spin Labeling (SDSL), and deuterium labeled amino acids have been utilized to determine the local secondary structure of an α-helical model peptide, where i+4 positions show larger ESEEM peaks than i+3 positions. Due to the turn periodicities of an α-helix (3.6 residues per turn) and a 310-helix (3.1 residues per turn), it was hypothesized that the opposite deuterium modulation pattern would be observed for a 310-helix. In this study, an amphipathic model peptide, LRL8, was used where 2H-labeled <i>d</i>10-leucine (Leu) was substituted at a specific Leu residue, and a nitroxide spin label was positioned 2, 3,  and 4 residues away (denoted i+2 to i+4). Once labeled, it was determined that the peptide adopts different structures based on the matrix. In trifluoroethanol (TFE), the peptide adopts an α-helical structure, and when incorporated into liposomes the peptide adopts a 310-helix secondary structure. The 2H peaks in the FT frequency domain data demonstrated larger peaks for the i+4 samples compared to the i+3 samples for the α-helix, and the opposite pattern was observed for the 310-helix. These unique patterns provide structural information to distinguish between α-helix and 310-helical secondary structures for the first time using ESEEM spectroscopy. This technique utilizes a shot data acquisition time (~1hour) and small sample concentrations (μg), while providing more site-specific information as compared to traditional biophysical approaches such as circular dichroism.

Utilizing electron spin echo envelope modulation to distinguish between the local secondary structures of an α-helix and an amphipathic 310-helical peptide

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.