Insights Into the Micelle-Induced β-Hairpin-to-α-Helix Transition of a LytA-Derived Peptide by Photo-CIDNP Spectroscopy

A choline-binding module from pneumococcal LytA autolysin, LytA(239-252,) was reported to have a highly stable nativelike beta-hairpin in aqueous solution, which turns into a stable amphipathic alpha-helix in the presence of micelles. Here, we aim to obtain insights into this DPC-micelle triggered beta-hairpin-to-alpha-helix conformational transition using photo-CIDNP NMR experiments. Our results illustrate the dependency between photo-CIDNP phenomena and the light intensity in the sample volume, showing that the use of smaller-diameter (2.5 mm) NMR tubes instead of the conventional 5 mm ones enables more efficient illumination for our laser-diode light setup. Photo-CIDNP experiments reveal different solvent accessibility for the two tyrosine residues, Y249 and Y250, the latter being less accessible to the solvent. The cross-polarization effects of these two tyrosine residues of LytA(239-252) allow for deeper insights and evidence their different behavior, showing that the Y250 aromatic side chain is involved in a stronger interaction with DPC micelles than Y249 is. These results can be interpreted in terms of the DPC micelle disrupting the aromatic stacking between W241 and Y250 present in the nativelike beta-hairpin, hence initiating conversion towards the alpha-helix structure. Our photo-CIDNP methodology represents a powerful tool for observing residue-level information in switch peptides that is difficult to obtain by other spectroscopic techniques.

Automated summary

In this study, the conformational transition of LytA(239-252) triggered by DPC micelles was investigated using photo-CIDNP NMR experiments. The results revealed different solvent accessibility and interaction behavior between the two tyrosine residues, Y249 and Y250, providing insights into the disruption of aromatic stacking and initiation of structure conversion towards the alpha-helix. The photo-CIDNP methodology proved to be a powerful tool for observing residue-level information that is difficult to obtain by other spectroscopic techniques.