Interaction of 'toxic' and 'immunogenic' A-gliadin peptides with a membrane-mimetic environment.

Celiac disease (CD) is characterized by abnormally high concentrations of certain peptides in the small bowel. These peptides can be grouped in 'toxic' and 'immunogenic' classes, which elicit an innate immune response and an HLA-mediated adaptive response, respectively. It is not clear on which molecular mechanisms responses to these different classes are based, but the 31-43 (P31-43) and the 56-68 (P56-68) A-gliadin fragments are usually adopted as sequence representatives of toxic and immunogenic peptides, respectively. Here we report fluorescence experiments aiming to mimic the interaction of these peptides with the cell membrane surface by using sodium dodecyl sulphate (SDS) as a membrane-mimetic medium. We show that P31-43 is able to bind SDS micelles in a way that resembles mixed micelle formation. On the other hand, no binding at all could be detected for P56-68. This different behaviour could be related to the paracellular or transcellular route through which gluten peptides may cross the intestinal epithelium, and open new insights into the pathogenetic mechanisms of CD.

Entrapment of Aß(1-40) peptide in unstructured aggregates.

Recognizing the complexity of the fibrillogenesis process provides a solid ground for the development of therapeutic strategies aimed at preventing or inhibiting protein-protein aggregation. Under this perspective, it is meaningful to identify the possible aggregation pathways and their relative products. We found that Aß-peptide dissolved in a pH 7.4 solution at small peptide concentration and low ionic strength forms globular aggregates without typical amyloid ß-conformation. ThT binding kinetics was used to monitor aggregate formation. Circular dichroism spectroscopy, AFM imaging, static and dynamic light scattering were used for structural and morphological characterization of the aggregates. They appear stable or at least metastable with respect to fiber growth, therefore appearing as an incidental product in the pathway of fibrillogenesis.