Sequence length dependence in arginine/phenylalanine oligopeptides: Implications for self-assembly and cytotoxicity

Abstract

We present a detailed study on the self-assembly and cytotoxicity of arginine-rich fragments with general form [RF] (n=1-5). These highly simplified sequences, containing only two l-amino acids, provide suitable models for exploring both structure and cytotoxicity features of arginine-based oligopeptides. The organization of the sequences is revealed over a range of length scales, from the nanometer range down to the level of molecular packing, and their cytotoxicity toward C6 rat glioma and RAW264.7 macrophage cell lines is investigated. We found that the polymorphism is dependent on peptide length, with a progressive increase in crystalline ordering upon increasing the number of [RF] pairs along the backbone. A dependence on length was also found for other observables, including critical aggregation concentrations, formation of chiral assemblies and half maximum inhibitory concentrations (IC). Whereas shorter peptides self-assemble into fractal-like aggregates, clear fibrillogenic capabilities are identified for longer sequences with octameric and decameric chains exhibiting crystalline phases organized into cross-β structures. Cell viability assays revealed dose-dependent cytotoxicity profiles with very similar behavior for both glioma and macrophage cell lines, which has been interpreted as evidence for a nonspecific mechanism involved in toxicity. We propose that structural organization of [RF] peptides plays a paramount role regarding toxicity due to strong increase of local charge density induced by self-assemblies rich in cationic groups when interacting with cell membranes.

β‐sheet assembly in amyloidogenic glutamic acid nanostructures: Insights from X‐ray scattering and infrared nanospectroscopy

“…In fact, the propensity of aromatic side chains at adjacent strands to establish π‐π interactions likely favors the growth of β ‐ sheets where peptide backbones appear perpendicularly oriented to the long axis of the supramolecular arrangement. These characteristics are critical for appearance of the cross ‐ β structure revealed by our diffraction data and they are consistent with the organization previously found in intercalating arginine/phenylalanine oligopeptides …”

“…These characteristics are critical for appearance of the cross-β structure revealed by our diffraction data and they are consistent with the organization previously found in intercalating arginine/phenylalanine oligopeptides. 15,16,61…”

Hybrid Hydrogels Based on Polyethylene Glycol Bioconjugated with Silylated‑Amyloidogenic Peptides

“…38 The [RF] 4 system has been widely studied, proving that it features the formation of cylinders above the cac (critical aggregation concentration). [22][23][24] Such behavior was also observed for compound 1, demonstrating that the addition of the silane group and the glycine residues did not interfere in the system morphology ( Figure S5c, SI section). The cylinder radius can be estimated using the p(r) curve, which corresponds to the inflection point of the curve at its maximum peak.…”

“…22 Another interesting feature was the interconnection of the fibers, which formed an entangled network that is extremely important in gel formation. The characteristics found for the silane peptide are similar to only [RF] 4 compound materials, [22][23][24] suggesting that the silane group retains the characteristic of conformation-rich fibrillar structures. An amorphous structure extent in all the images of compound 2 was detected, which is a feature of synthetic polymers (Figure 5b).…”

“…Molecular self-assembly of oligopeptides into wellordered nanostructures provides models to explore the development of new materials. 14 We have recently shown [22][23][24] a systematic fibrillation behavior of an alternating [RF] n=1-5 peptide (where R: L-arginine, F: L-phenylalanine), which exhibit physicochemical properties of β-amyloid proteins.…”