Amyloid fiber formation by synthetic peptides derived from the sequence of the protein CsgA of Escherichia coli.

We characterized the formation of amyloid fibers by two peptides derived from the CsgA sequence: R5 (133- 151) corresponding to the whole repeating unit R5 and a truncated form of this peptide called R5T (134-143). In the presence of either of the two peptides: an increase in the fluorescence intensity of Thioflavin T was observed; a shift of the absorbance of Congo red was measured; spontaneous formation of amyloid fibers was observed by polarized light as well asatomic force microscopy imaging. Large-size aggregates were observed with R5 while R5T formed fagots of individualized fibers. The infrared spectroscopy analysis revealed the presence of a greater number of intermolecular bonds for R5. In conclusion, a 10 aminoacids peptide derived from the R5 sequence was sufficient for the spontaneous formation of amyloid fibrils but not to form large-size aggregates of fibers.