Circular dichroism and electron microscopy studies in vitro of 33-mer gliadin peptide revealed secondary structure transition and supramolecular organization

• Published in: Biopolymers 2014-01, Vol.101 (1), p.96-106
• Main Authors: Herrera, María G., Zamarreño, Fernando, Costabel, Marcelo, Ritacco, Hernan, Hütten, Andreas, Sewald, Norbert, Dodero, Verónica I.
• Format: Article
• Language: English
• Subjects: 33-mer gliadin peptide; Biopolymers; Circular Dichroism; Electron microscopy; Gliadin; gliadin intolerance; Hordeum vulgare; In vitro testing; Microscopy, Electron; Nanospheres; Organizations; Peptide Fragments - chemistry; Peptides; Peptides - chemistry; Self assembly; supramolecular organization; Triticum aestivum
• ISSN: 0006-3525; 1097-0282
• DOI: 10.1002/bip.22288

ABSTRACT Gliadin, a protein present in wheat, rye, and barley, undergoes incomplete enzymatic degradation during digestion, producing an immunogenic 33‐mer peptide, LQLQPF(PQPQLPY)3PQPQPF. The special features of 33‐mer that provoke a break in its tolerance leading to gliadin sensitivity and celiac disease remains elusive. Herein, it is reported that 33‐mer gliadin peptide was not only able to fold into polyproline II secondary structure but also depending on concentration resulted in conformational transition and self‐assembly under aqueous condition, pH 7.0. A 33‐mer dimer is presented as one initial possible step in the self‐assembling process obtained by partial electrostatics charge distribution calculation and molecular dynamics. In addition, electron microscopy experiments revealed supramolecular organization of 33‐mer into colloidal nanospheres. In the presence of 1 mM sodium citrate, 1 mM sodium borate, 1 mM sodium phosphate buffer, 15 mM NaCl, the nanospheres were stabilized, whereas in water, a linear organization and formation of fibrils were observed. It is hypothesized that the self‐assembling process could be the result of the combination of hydrophobic effect, intramolecular hydrogen bonding, and electrostatic complementarity due to 33‐mer's high content of proline and glutamine amino acids and its calculated nonionic amphiphilic character. Although, performed in vitro, these experiments have revealed new features of the 33‐mer gliadin peptide that could represent an important and unprecedented event in the early stage of 33‐mer interaction with the gut mucosa prior to onset of inflammation. Moreover, these findings may open new perspectives for the understanding and treatment of gliadin intolerance disorders. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 96–106, 2014.