Self-assembly of 33-mer gliadin peptide oligomers

HERRERA, M.G; BENEDINI, L.A.; LONEZ, C; SCHILARDI. P.L; HELLWEG, T.; RUYSSCHAERT , J-M; DODERO.V.I

SOFT MATTER

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2015

1744-683X

The 33-mer gliadin peptide, LQLQPF(PQPQLPY)3PQPQPF, is a highly immunogenic peptide involved in celiac disease and probably in other immune pathologies associated to gliadin. Herein, dynamic light scattering measurements showed that 33-mer, in the micromolar concentration range, forms polydisperse particles nano- and micrometer range in aqueous media. This behaviour is reminiscent of classical association of colloids and we hypothesized that 33-mer peptide is able to self-assemble into micelles which are the precursors of 33-mer oligomers in water. Deposition of 33-mer peptide aqueous solution on bare mica and observation by atomic force microscopy revealed nano- and microstructures with different morphology. At 6 µM isolated nanospherical structures and their clusters were detected. In addition, in the concentration range from 60 to 250 µM, the spherical oligomers were associated mainly in linear and annular arrangements and structures adopting a ?sheet? type morphology appeared. At higher concentrations (610 µM), it was possible to detect mainly filaments and plaques immersed in a background of nanospherical structures. The self-assembly process could be qualitatively and quantitatively explained by considering a diffusion limited aggregation (DLA) behaviour with fractal dimension in the range of 1.62 ± 0.02 to 1.73 ± 0.03. Analysing the morphology of the structures at 610 µM, a nucleated DLA mechanism is proposed, in which the filaments could be considered as nucleus of further oligomerization. Secondary structure evaluation of the oligomers by Attenuated Total Reflection FTIR spectroscopy (ATR-FTIR) revealed the existence of a conformational equilibrium of self-assembled structures, from an extended conformation to a more folded parallel beta elongated structures. The latest conformation is being favoured at increasing concentrations. Our findings provide structural information about 33-mer peptide supramolecular organization which might open the way to new perspectives in the understanding and treatment of gliadin intolerance disorders.