Effect of temperature on self-assembly of an ionic tetrapeptide

The self-aggregation of the ionic tetrapeptide RWDW (R = arginine, W = tryptophan, D = aspartic acid) was studied at three temperatures (15, 25 and 35 degrees C) by different experimental techniques such as atomic force microscopy (AFM), isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). AFM was used to investigate the morphology of the aggregates; the AFM images at 15 degrees C showed the presence of a dense network of entangled fibres, while at 35 degrees C the peptide assembled into sparse globular and fibrillar structures. Moreover, the calorimetric experiments showed that in all cases the disaggregation process is endothermic and dependent on the investigated temperature. Both the enthalpy of disaggregation and the cac change with temperature. In particular, at 35 degrees C, we obtained the lower enthalpy of disaggregation and higher cac, showing that the disaggregation process is favoured at high temperature. The DSC scans strengthen the hypothesis that the RWDW aggregation is a rather complex phenomenon.