Evidence of π‐stacking interactions in the self‐assembly of hIAPP_22‐29

Abstract

The role aromatic amino acids play in the formation of amyloid is a subject of controversy. In an effort to clarify the contribution of aromaticity to the self-assembly of hIAPP22–29, peptide analogs containing electron donating groups (EDGs) or electron withdrawing groups (EWGs) as substituents on the aromatic ring of Phe-23 at the para position have been synthesized and characterized using turbidity measurements in conjunction with Raman, and fluorescence spectroscopy. Results indicate the incorporation of EDGs on the aromatic ring of Phe-23 virtually abolish the ability of hIAPP22–29 to form amyloid. Peptides containing EWGs were still capable of forming aggregates. These aggregates were found to be rich in β-sheet secondary structure. TEM images of the aggregates confirm the presence of amyloid fibrils. The observed difference in amyloidogenic propensity between peptides containing EDGs and those with EWGs appears not to be based on differences in peptide hydrophobicity. Fluorescence and Raman spectroscopic investigations reveal that the environment surrounding the aromatic ring becomes more hydrophobic and ordered upon aggregation. Furthermore, Raman measurements of peptide analogs containing EWGs, conclusively demonstrate a distinct downshift in the -C=C- ring mode (ca. 1600 cm−1) upon aggregation that has previously been shown to be indicative of π-stacking. While previous work has demonstrated that π-stacking is not an absolute requirement for fibrillization, our findings indicate that Phe-23 also contributes to fibril formation through π-stacking interactions and that it is not only the hydrophobic nature of this residue that is relevant in the self-assembly of hIAPP22–29.

Aromaticity and amyloid formation: Effect of π-electron distribution and aryl substituent geometry on the self-assembly of peptides derived from hIAPP22–29

“…The (COOH)Phe peptide ( 11 ) was also found to aggregate quite slowly. TEM has previously shown that peptides 1 , 6 , 8 , and 9 form amyloid fibrils whereas 7 was found to form helical tapes [45]. TEM imaging of aggregates produced by peptide 11 reveal fibril morphology similar to that of the other aggregating peptides (Fig.…”

“…In contrast, electron withdrawing groups (EWGs) do not have as drastic effect [45]. Furthermore, our findings indicate that peptides containing EDGs fail to form any type of π-stacking interactions.…”

“…2–4 illustrates the results of turbidity measurements. The amyloidogenic propensities of some of these peptides have previously been characterized but are included for comparison purposes [45]. From the turbidity data it is abundantly clear that peptides 2 , 3 , 4 , 5 and 10 which contain EDGs are universally incapable of forming amyloid (Fig.…”

“…Peptides based on hIAPP 22–29 were synthesized as previously described [45]. Peptides based on hIAPP 20–29 were synthesized manually using Rink amide resin (substitution level 0.59 mmol/g) via a standard Fmoc-solid phase synthesis protocol using N , N , N ′, N ′-Tetramethyl- O -(1 H -benzotriazol-1-yl)uranium hexafluorophosphate (HBTU), 1-Hydroxy-benzotriazole (HOBT) as activating agents.…”

Next-Generation Nanoantibacterial Tools Developed from Peptides

“…In this context, AMPs are remarkable alternative polymers for preparing nanofibers to perform dual strategies in biomedical engineering. Several potential applications of nanofibers have been documented, such as wound healing, drug delivery, controlled release, manipulation of surface properties, immobilization of antibiotics or enzymes and coating on biomedical devices, which opens a new avenue in biomedical sciences [126,127] (Figure 4).…”