SAXS-WAXS monitoring of the amyloid fibril assembly of a hormone peptide analogue upon pH change.

Amyloid structures represent one of the most widespread and stable protein folding in nature. This particular folding can be either beneficial or detrimental to its host organism depending on the conditions and places of aggregation. Consequently, the space and time control of their formation mechanisms of amyloid fibril formation is crucial. In the present work, we have investigated the assembly properties of the terlipressin (TLP), a peptide analogue of the vasopressin hormone that is known – like many other peptide hormones – to be stored under the form of reversible amyloid fibrils, which suggests a finely tuned aggregation process. In particular, the assembly kinetics has been monitored by small and wide-angle x-ray scattering (SAXS-WAXS). In combination with circular dichroism, ATR-FTIR and cryoTEM characterization, this analysis reveals that the TLP assembly goes through the formation of on-pathway transitory amorphous aggregates in which the amyloid fibrils nucleate. At the end of the process, the “amyloid phase” (i.e., the fibrils) is in dynamic equilibrium with the liquid phase (peptide monomers). The proportion between the two phases depends on the pH and peptide concentration. Finally, the reversibility of the assembly is assessed.