Sensing site‐specific structural characteristics and chirality using vibrational circular dichroism of isotope labeled peptides

Abstract

Isotope labeling has a long history in chemistry as a tool for probing structure, offering enhanced sensitivity, or enabling site selection with a wide range of spectroscopic tools. Chirality sensitive methods such as electronic circular dichroism are global structural tools and have intrinsically low resolution. Consequently, they are generally insensitive to modifications to enhance site selectivity. The use of isotope labeling to modify vibrational spectra with unique resolvable frequency shifts can provide useful site-specific sensitivity, and these methods have been recently more widely expanded in biopolymer studies. While the spectral shifts resulting from changes in isotopic mass can provide resolution of modes from specific parts of the molecule and can allow detection of local change in structure with perturbation, these shifts alone do not directly indicate structure or chirality. With vibrational circular dichroism (VCD), the shifted bands and their resultant sign patterns can be used to indicate local conformations in labeled biopolymers, particularly if multiple labels are used and if their coupling is theoretically modeled. This mini-review discusses selected examples of the use of labeling specific amides in peptides to develop local structural insight with VCD spectra.

Mini review: Instrumentation for vibrational circular dichroism spectroscopy, still a role for dispersive instruments

“…With the addition of VCD to IR, the sign pattern can often yield structural information beyond the shift. Such an approach is most applicable for polymer or oligomer samples where two or more residues can be labeled and the VCD pattern used to determine local conformation …”

“…Such an approach is most applicable for polymer or oligomer samples where two or more residues can be labeled and the VCD pattern used to determine local conformation. 92,[98][99][100][101][102] We have undertaken several studies with this approach, which has proven particularly useful in combination with theoretical simulations of the spectra for the labeled peptides. A particularly striking example is for labeled Lys 14 oligomers, as shown in Figure 8, where two residues in the center of the oligomer sequence were labeled with 13 C on the amide C═O, either in sequence, K14T (blue) or alternate, K14A (red).…”

Isotopically Site-Selected Dynamics of a Three-Stranded β-Sheet Peptide Detected with Temperature-Jump Infrared-Spectroscopy

“…Previously, we used the Xxx- D Pro amide I′ band (I′ indicates H–D exchanged) to monitor some aspects of the turn because such tertiary amides yield a uniquely resolved, lower amide I′ frequency, but in most cases, their dynamics were not distinguishable from those of the strand. , A more precise and selective approach is to substitute the amide CO with 13 C which leads to a shift of ∼40 cm –1 down in frequency for the associated amide I′ band (if viewed as uncoupled from other amides). This normally results in a feature that is shifted outside the residual 12 C amide I′ bandwidth that can be used to monitor changes in the local structure. − …”

Instrumentation for Vibrational Circular Dichroism Spectroscopy: Method Comparison and Newer Developments

“…Spectra for structures as large as globular proteins have been successfully simulated using this method [ 153 ]. Alternatively, isotope labeling can be introduced to the peptide sequence to spectrally shift the contributions of a local part of the biopolymer, and with computational modeling of VCD spectra for possible structural variants, local conformations can be deduced [ 100 , 154 , 155 , 156 , 157 , 158 , 159 , 160 ].…”