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

M Victoria Gomez,Ruth M Gschwind,Philipp Nitschke,Margarita Ruiz-Castañeda,M Angeles Jiménez

doi:10.3390/ijms22136666

Abstract

A choline-binding module from pneumococcal LytA autolysin, LytA239–252, was reported to have a highly stable nativelike β-hairpin in aqueous solution, which turns into a stable amphipathic α-helix in the presence of micelles. Here, we aim to obtain insights into this DPC-micelle triggered β-hairpin-to-α-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 LytA239–252 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 β-hairpin, hence initiating conversion towards the α-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.

Highlights

The conformational transitions of peptides and proteins are in the crosshairs of several research fields
The potential of the photo-CIDNP nuclear magnetic resonance (NMR) technique is outlined for the identification of solvent-accessible aromatic residues within a peptide sequence to understand the interaction between the LytA239–252 peptide and DPC micelles
In our case of study, photo-CIDNP experiments revealed that Tyr residues from the LytA239–252 peptide were distinctly exposed to the solvent; more precisely, Y250 was less exposed to the solvent in the aqueous solution due to aromatic stacking than Y249 was and became more hindered in the presence of increasing DPC amounts as illustrated by the lower signal enhancement for the primary polarizations compared with Y249

Summary

Introduction

The conformational transitions of peptides and proteins are in the crosshairs of several research fields. Structural transitions are a common subject in most neurodegenerative diseases, in which uncontrolled changes in the native structure of proteins trigger pathogenesis [3,4,5]. Along this line, one of the most popular examples is the conversion of the β-amyloid peptide from a soluble unstructured ensemble of conformations into a “double-horseshoe-like cross-β-sheet” [6,7] that is associated with the onset of Alzheimer’s disease. Conformational transitions are key to emerging fields, including nanobiotechnology or de novo

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Methods

Conclusion