pH- and concentration-dependent supramolecular assembly of a fungal defensin plectasin variant into helical non-amyloid fibrils

Abstract

Self-assembly and fibril formation play important roles in protein behaviour. Amyloid fibril formation is well-studied due to its role in neurodegenerative diseases and characterized by refolding of the protein into predominantly β-sheet form. However, much less is known about the assembly of proteins into other types of supramolecular structures. Using cryo-electron microscopy at a resolution of 1.97 Å, we show that a triple-mutant of the anti-microbial peptide plectasin, PPI42, assembles into helical non-amyloid fibrils. The in vitro anti-microbial activity was determined and shown to be enhanced compared to the wildtype. Plectasin contains a cysteine-stabilised α-helix-β-sheet structure, which remains intact upon fibril formation. Two protofilaments form a right-handed protein fibril. The fibril formation is reversible and follows sigmoidal kinetics with a pH- and concentration dependent equilibrium between soluble monomer and protein fibril. This high-resolution structure reveals that α/β proteins can natively assemble into fibrils.

Amyloid‐Based Albumin Hydrogels

“…The assembly of high aspect ratio structures does not necessarily designate amyloid fibril formation, [ 57,60–62 ] nor is there a single type of amyloid fibril, as polymorphism was previously shown in various systems. [ 15,33 ] Secondary structure characterization of the fibrils prepared through TCEP‐treatment of albumin confirmed the presence of beta‐sheet formation, which was further corroborated by ThT fluorescence measurements, validating the presence of amyloid‐like fibrils.…”

“…At acidic pH (3.6), below the isoelectric point of albumin, the surface charge of the fibrils was positive and fibrils were thicker. A more detailed structural analysis using X‐ray scattering [ 10,57 ] and/or electron microscopy techniques [ 60 ] could provide the atomic‐scale structure of the formed fibrils in the future.…”

Chiral supramolecular nanomaterials: From chirality transfer and amplification to regulation and applications

“…The reversal of helicity is frequently caused by alterations in pH, which induce changes in peptide conformation and interactions among amino acid-based building blocks. [47,48] Kanagaraj et al presented γ-cyclodextrin (γ-CDx) analogs as chiral hosts for the photocyclodimerization of 2-anthracenecarboxylic acid (AC). [35] The investigation focused on the impact of pH on the photoreactivity and the resulting stereochemistry of the photoproducts.…”

“…The reversal of helicity is frequently caused by alterations in pH, which induce changes in peptide conformation and interactions among amino acid‐based building blocks. [ 47,48 ]…”

Controllably Self-Assembled Antibacterial Nanofibrils Based on Insect Cuticle Protein for Infectious Wound Healing

“…In general, proteins can self-assemble to supramolecular ordered structures upon various chemical and biological stimuli such as pH, enzyme, salts, etc., − driven by noncovalent interactions. − The as-formed self-assemblies can be used as highly biocompatible biofunctional materials, which demonstrate broad potential applications in drug delivery, tissue engineering, and so on. − For example, Champion et al reported that the protein synthesized from elastin-like polypeptide could arrange into vesicles via hydrophobic interactions between protein molecules under appropriate pH values, which may present great potential in drug-delivery applications . Li et al developed a hydrogel formed via self-assembly of a glycopeptide through enzymatic action of alkaline phosphatase, which can work as an effective matrix to trigger the generation of blood capillaries .…”