Isotope-edited Infrared Spectroscopy of 3-10 Helical Peptides

Abstract

Infrared spectroscopy (IR) is a valuable tool for probing the conformation and dynamics of peptides. The amide I band is particularly sensitive to the strength and position of the hydrogen bonds that define secondary structure. Site-specific structural information can be obtained by sequential, systematic isotope labeling of the backbone (1). In this study, isotope-edited infrared spectroscopy was applied for the elucidation of residue level structural information of model 3-10 hexameric peptides. A series of peptides comprised of four aminoisobutyric acid (Aib) and two α-methyl valine residues were prepared to include two 13C labels at the N-terminus, middle and C-terminus positions (2). The IR spectra were measured in CDCl3 solution. Far-ultraviolet circular dichroism spectra in 2, 2, 2- trifluoroethanol confirmed 3-10 helical structure for all peptides. The spectral features of the 12C and 13C amide I depend on the position of the isotope label and the nature of the buffer. These differences are discussed in terms of the x-ray structure of the peptides and the details of the 3-10 helical conformation.1. Decatur, S.M. (2006) Accounts of Chemical Research 39:169-175.2. Maekawa, H.; Toniolo, C.; Broxterman, Q.B.; Ge, N.H. (2007) J. Phys. Chem B. 111, 3222-3235.