Could you explain the significance of your article to the non-specialist?

Gamma-turns are secondary structures of peptides and protein chains. The use of short model peptide chains enables us to isolate such structures and to study their interactions with the rest of the molecule. Isolation in the gas phase combined with laser spectroscopy (in both near UV and IR) allows us to examine precisely the interactions stabilising the structure, in particular the H-bonding network. Thus, the two helical forms of a gamma-turn can be easily distinguished from their different interactions with a nearby phenylalanine UV chromophore; in addition, their relative abundance in the gas phase also enables determining directly the most efficient recognition configuration, which is very difficult to perform using other methods, including quantum chemistry.

What has motivated you to conduct this work?

Our group had the experience of laser desorption and supersonic expansion in order to prepare and cool down the peptide chain in the vacuum. Previous works had also enabled a mapping of the interactions from their IR spectral signatures. This experience enables a straightforward assignment of the structures observed as well as an effective estimate of the interactions involved.

Where do you see this work developing in the future?

We target gas phase isolation of larger peptide chains, capable of forming larger secondary structures, like beta-hairpins or helical structures, like 3-10 or alpha helices. The challenge in the case of such larger species will be to still obtain resolved UV and IR spectral features, which is the key for a local description of structures through their H-bonding network.

Are there any particular challenges facing future research in this area?

An interesting complementary experiment would be to measure precisely the relative energy of such two diastereoisomeric forms. The feasibility of such a measurement, based on the observation of a laser-induced isomerisation in a supersonic expansion, has been recently demonstrated for a simple flexible molecule. It would be of great interest in the present case, especially because the energy difference, on which the present molecular recognition is based, is small (< 1 kcal/mol), much smaller than the precision expected from quantum chemistry calculations.