Tryptophan self-assembly yields cytotoxic nanofibers containing amyloid-mimicking and cross-seeding competent conformers

Molecular insights into the phase transition of lysozyme into amyloid nanostructures: Implications of therapeutic strategies in diverse pathological conditions

Lysozyme, a well-known bacteriolytic enzyme, exhibits a fascinating yet complex behavior when it comes to protein aggregation. Under certain conditions, this enzyme undergoes flexible transformation, transitioning from partially unfolded intermediate units of native conformers into complex cross-β-rich nano fibrillar amyloid architectures. Formation of such lysozyme amyloids has been implicated in a multitude of pathological and medical severities, like hepatic dysfunction, hepatomegaly, splenic rupture as well as spleen dysfunction, nephropathy, sicca syndrome, renal dysfunction, renal amyloidosis, and systemic amyloidosis. In this comprehensive review, we have attempted to provide in-depth insights into the aggregating behavior of lysozyme across a spectrum of variables, including concentrations, temperatures, pH levels, and mutations. Our objective is to elucidate the underlying mechanisms that govern lysozyme's aggregation process and to unravel the complex interplay between its structural attributes. Moreover, this work has critically examined the latest advancements in the field, focusing specifically on novel strategies and systems, that have been implemented to delay or inhibit the lysozyme amyloidogenesis. Apart from this, we have tried to explore and advance our fundamental understanding of the complex processes involved in lysozyme aggregation. This will help the research community to lay a robust foundation for screening, designing, and formulating targeted anti-amyloid therapeutics offering improved treatment modalities and interventions not only for lysozyme-linked amyloidopathy but for a wide range of amyloid-related disorders.

Transformable Supramolecular Self-Assembled Peptides for Cascade Self-Enhanced Ferroptosis Primed Cancer Immunotherapy

Immunotherapy has received widespread attention for its effective and long-term tumor-eliminating ability. However, for immunogenic "cold" tumors, such as prostate cancer (PCa), the low immunogenicity of the tumor itself is a serious obstacle to efficacy. Here, this work reports a strategy to enhance PCa immunogenicity by triggering cascade self-enhanced ferroptosis in tumor cells, turning the tumor from "cold" to "hot". This work develops a transformable self-assembled peptide TEP-FFG-CRApY with alkaline phosphatase (ALP) responsiveness and glutathione peroxidase 4 (GPX4) protein targeting. TEP-FFG-CRApY self-assembles into nanoparticles under aqueous conditions and transforms into nanofibers in response to ALP during endosome/lysosome uptake into tumor cells, promoting lysosomal membrane permeabilization (LMP). On the one hand, the released TEP-FFG-CRAY nanofibers target GPX4 and selectively degrade the GPX4 protein under the light irradiation, inducing ferroptosis; on the other hand, the large amount of leaked Fe2+ further cascade to amplify the ferroptosis through the Fenton reaction. TEP-FFG-CRApY-induced immunogenic ferroptosis improves tumor cell immunogenicity by promoting the maturation of dendritic cells (DCs) and increasing intratumor T-cell infiltration. More importantly, recovered T cells further enhance ferroptosis by secreting large amounts of interferon-gamma (IFN-γ). This work provides a novel strategy for the molecular design of synergistic molecularly targeted therapy for immunogenic "cold" tumors.

Pleiotropic Nanostructures Built from l-Histidine Show Biologically Relevant Multicatalytic Activities

The essential amino acid histidine plays a central role in the manifestation of several metabolic processes, including protein synthesis, enzyme-catalysis, and key biomolecular interactions. However, excess accumulation of histidine causes histidinemia, which shows brain-related medical complications, and the molecular mechanism of such histidine-linked complications is largely unknown. Here, we show that histidine undergoes a self-assembly process, leading to the formation of amyloid-like cytotoxic and catalytically active nanofibers. The kinetics of histidine self-assembly was favored in the presence of Mg(II) and Co(II) ions. Molecular dynamics data showed that preferential noncovalent interactions dominated by H-bonds between histidine molecules facilitate the formation of histidine nanofibers. The histidine nanofibers induced amyloid cross-seeding reactions in several proteins and peptides including pathogenic Aβ1-42 and brain extract components. Further, the histidine nanofibers exhibited oxidase activity and enhanced the oxidation of neurotransmitters. Cell-based studies confirmed the cellular internalization of histidine nanofibers in SH-SY5Y cells and subsequent cytotoxic effects through necrosis and apoptosis-mediated cell death. Since several complications including behavioral abnormality, developmental delay, and neurological disabilities are directly linked to abnormal accumulation of histidine, our findings provide a foundational understanding of the mechanism of histidine-related complications. Further, the ability of histidine nanofibers to catalyze amyloid seeding and oxidation reactions is equally important for both biological and materials science research.

Interactions between Lipid Vesicle Membranes and Single Amino Acid Fibrils: Probable Origin of Specific Neurological Disorders

Amyloid fibrils are known to be responsible for several neurological disorders, like Alzheimer's disease (AD), Parkinson's disease (PD), etc. For decades, mostly proteins and peptide-based amyloid fibrils have been focused on, and the topic has acknowledged the rise, development, understanding of, and controversy, as well. However, the single amino acid based amyloid fibrils, responsible for several disorders, such as phenylketonuria, tyrosenimia type II, hypermethioninemia, etc., have gotten scientific attention lately. To understand the molecular level pathogenesis of such disorders originated due to the accumulation of single amino acid-based amyloid fibrils, interaction of these fibrils with phospholipid vesicle membranes is found to be an excellent cell-free in vitro setup. Based on such an in vitro setup, these fibrils show a generic mechanism of membrane insertion driven by electrostatic and hydrophobic effects inside the membrane that reduces the integral rigidity of the membrane. Alteration of such fundamental properties of the membrane, therefore, might be referred to as one of the prime pathological factors for the development of these neurological disorders. Hence, such interactions must be investigated in cellular and intracellular compartments to design suitable therapeutic modulators against fibrils.

Initiation of Brain Extract Fibrillation and Effective Cellular Internalization of Tryptophan Fibrils Unveils Its Neurotoxicity Risk

Recent discoveries on the self-assembly of aromatic amino acids into amyloid-like neurotoxic nanostructures have initiated a quest to decode the molecular mechanisms for the initiation of neurodegeneration. Moreover, the multicomponent nature of the amyloid deposits still questions the existing and well-defined amyloid cascade hypothesis. Hence, deciphering the neurotoxicity of amyloid-like nanostructures of aromatic amino acids becomes crucial for understanding the etiology of amyloidogenesis. Here, we demonstrate the cellular internalization and consequential damaging effects of self-assembled amyloid-like tryptophan nanostructures on human neuroblastoma cells. The cell-damaging potential of tryptophan nanostructure seems to be facilitated via ROS generation, necrosis and apoptosis mediated cell death. Further, tryptophan nanostructures were found to be seeding competent conformers, which triggered aggressive aggregation of brain extract components. The early stage intermediate nanostructures possess a higher cross-seeding efficacy than the seeding potential of the matured tryptophan fibrils. In addition to the cell-damaging and cross-seeding effects, tryptophan fibrils were found to catalyze oxidation of neuromodulator dopamine. These findings add more insights into the specific role of tryptophan self-assembly during the pathogenesis of hypertryptophanemia and other amyloid-associated neurodegenerative complications.

The self-assembly of L-histidine might be the cause of histidinemia

L-Histidine is an essential amino acid with unique biochemical and physiological properties. Histidinemia is a disease condition caused by the elevated level of L-histidine in our blood. Mutations in the histidase, an enzyme for the breakdown of histidine, is the cause of the rise in histidine concentration. To our knowledge, no research has been done on why a high concentration of histidine causes histidinemia. In this study, we provide a potential explanation why the elevated levels of histidine in the human body causes histidinemia. In this study we have found that L-histidine self-assembled in water to form nano sheet structures at physiological pH and temperature, using 1D 1H NMR spectroscopy, diffusion ordered spectroscopy (DOSY) and scanning electron microscope (SEM) techniques. The kinetics of self-assembly has been studied using real time NMR spectroscopy. We observed that both the aromatic ring and aliphatic part are equally contributing to the self-assembly of L-histidine. The symptoms of histidinemia, neurological deficits and speech delays, are similar to that of the neurodegenerative diseases caused by the self-assembly of peptides and proteins. We speculate that the self-assembly of L-histidine might be the cause of histidinemia.

A robust yet simple method to generate fluorescent amyloid nanofibers

Covalent tagging of fluorophores is central to the mechanistic understanding of important biological processes including protein-protein interaction and protein aggregation. Hence, studies on fluorophore-tagged peptides help in elucidating the molecular mechanism of amyloidogenesis, its cellular internalization, and crosstalk potential. Despite the many advantages the covalently tagged proteins offer, difficulties such as expensive and tedious synthesis and purification protocols have become a matter of concern. Importantly, covalently tagged fluorophores could introduce structural constraints, which may influence the conformation of the monomeric and aggregated forms of proteins. Here, we describe a robust-yet-simple method to make fluorescent-amyloid nanofibers through a coassembly-reaction route that does not alter the aggregation kinetics and the characteristic β-sheet-conformers of resultant nanofibers. Fluorescent amyloid nanofibers derived from insulin, lysozyme, Aβ1-42, and metabolites were successfully fabricated in our study. Importantly, the incorporated fluorophores exhibited remarkable stability, remaining intact without leaching even after undergoing serial dilutions and prolonged storage periods. This method enables monitoring of cellular internalization of the fluorescent-amyloid-nanofibers and the detection of FRET-signals during interfibrillar interactions. This simple and affordable protocol may significantly help amyloid researchers working on both in vitro and animal models.

The Metabolostasis Network and the Cellular Depository of Aggregation-Prone Metabolites

The vital role of metabolites across all branches of life and their involvement in various disorders have been investigated for decades. Many metabolites are poorly soluble in water or in physiological buffers and tend to form supramolecular aggregates. On the other hand, in the cell, they should be preserved in a pool and be readily available for the execution of biochemical functions. We thus propose that a quality-control network, termed "metabolostasis", has evolved to regulate the storage and retrieval of aggregation-prone metabolites. Such a system should control metabolite concentration, subcellular localization, supramolecular arrangement, and interaction in dynamic environments, thus enabling normal cellular physiology, healthy development, and preventing disease onset. The paradigm-shifting concept of metabolostasis calls for a reevaluation of the traditional view of metabolite storage and dynamics in physiology and pathology and proposes unprecedented directions for therapeutic targets under conditions where metabolostasis is imbalanced.

Tryptophan-PNA gc Conjugates Self-Assemble to Form Fibers

Peptide nucleic acids and their conjugates to peptides can self-assemble and generate complex architectures. In this work, we explored the self-assembly of PNA dimers conjugated to the dipeptide WW. Our studies suggest that the indole ring of tryptophan promotes aggregation of the conjugates. The onset of fluorescence is observed upon self-assembly. The structure of self-assembled WWgc is concentration-dependent, being spherical at low concentrations and fibrous at high concentrations. As suggested by molecular modeling studies, fibers are stabilized by stacking interactions between tryptophans and Watson-Crick hydrogen bonds between nucleobases.