Keeping α-Synuclein at Bay: A More Active Role of Molecular Chaperones in Preventing Mitochondrial Interactions and Transition to Pathological States?

Intrinsic Disorder and Other Malleable Arsenals of Evolved Protein Multifunctionality

Microscopic evolution at the functional biomolecular level is an ongoing process. Leveraging functional and high-throughput assays, along with computational data mining, has led to a remarkable expansion of our understanding of multifunctional protein (and gene) families over the past few decades. Various molecular and intermolecular mechanisms are now known that collectively meet the cumulative multifunctional demands in higher organisms along an evolutionary path. This multitasking ability is attributed to a certain degree of intrinsic or adapted flexibility at the structure-function level. Evolutionary diversification of structure-function relationships in proteins highlights the functional importance of intrinsically disordered proteins/regions (IDPs/IDRs) which are highly dynamic biological soft matter. Multifunctionality is favorably supported by the fluid-like shapes of IDPs/IDRs, enabling them to undergo disorder-to-order transitions upon binding to different molecular partners. Other new malleable members of the protein superfamily, such as those involved in fold-switching, also undergo structural transitions. This new insight diverges from all traditional notions of functional singularity in enzyme classes and emphasizes a far more complex, multi-layered diversification of protein functionality. However, a thorough review in this line, focusing on flexibility and function-driven structural transitions related to evolved multifunctionality in proteins, is currently missing. This review attempts to address this gap while broadening the scope of multifunctionality beyond single protein sequences. It argues that protein intrinsic disorder is likely the most striking mechanism for expressing multifunctionality in proteins. A phenomenological analogy has also been drawn to illustrate the increasingly complex nature of modern digital life, driven by the need for multitasking, particularly involving media.

CRBN modulates synuclein fibrillation via degradation of DNAJB1 in mouse model of Parkinson disease

Cereblon (CRBN) is a substrate recruiter for CRL4CRBN E3 ubiquitin ligase system playing a plethora of pivotal roles for biological systems. Here, we identified DNAJB1 (DJ1) as endogenous substrate of CRBN and report how CRBN influences the aggregation and toxicity of alpha-synuclein (α-SYN) via modulation of DJ1. CRBN interferes with molecular activities of DJ1 in vitro, in cells, and in vivo resulting in a reduced disaggregation of α-SYN fibrils, increased formation of preformed fibrils (PFFs) of α-SYN, and high susceptibility of mice to MPTP and PFF-induced neurotoxicity. Depletion of Crbn improves the behavioral and biochemical responses of mice towards neurotoxic insult. Finally, we designed a peptide inhibitor to inhibit the recruitment of DJ1 to CRBN for ubiquitination, resulting in an enhanced supply of DJ1 to counteract the toxicity of aggregated α-SYN. Our data has important implications for development of CRBN-targeting therapies that could prevent or delay progression of neurodegenerative synucleinopathy.

Structural basis of substrate recognition and allosteric activation of the proapoptotic mitochondrial HtrA2 protease

The mitochondrial serine protease HtrA2 is a human homolog of the Escherichia coli Deg-proteins exhibiting chaperone and proteolytic roles. HtrA2 is involved in both apoptotic regulation via its ability to degrade inhibitor-of-apoptosis proteins (IAPs), as well as in cellular maintenance as part of the cellular protein quality control machinery, by preventing the possible toxic accumulation of aggregated proteins. In this study, we use advanced solution NMR spectroscopy methods combined with biophysical characterization and biochemical assays to elucidate the crucial role of the substrate recognizing PDZ domain. This domain regulates the protease activity of HtrA2 by triggering an intricate allosteric network involving the regulatory loops of the protease domain. We further show that divalent metal ions can both positively and negatively modulate the activity of HtrA2, leading to a refined model of HtrA2 regulation within the apoptotic pathway.

Realization of Amyloid-like Aggregation as a Common Cause for Pathogenesis in Diseases

Amyloids were conventionally referred to as extracellular and intracellular accumulation of Aβ42 peptide, which causes the formation of plaques and neurofibrillary tangles inside the brain leading to the pathogenesis in Alzheimer's disease. Subsequently, amyloid-like deposition was found in the etiology of prion diseases, Parkinson's disease, type II diabetes, and cancer, which was attributed to the aggregation of prion protein, α-Synuclein, islet amyloid polypeptide protein, and p53 protein, respectively. Hence, traditionally amyloids were considered aggregates formed exclusively by proteins or peptides. However, since the last decade, it has been discovered that other metabolites, like single amino acids, nucleobases, lipids, glucose derivatives, etc., have a propensity to form amyloid-like toxic assemblies. Several studies suggest direct implications of these metabolite assemblies in the patho-physiology of various inborn errors of metabolisms like phenylketonuria, tyrosinemia, cystinuria, and Gaucher's disease, to name a few. In this review, we present a comprehensive literature overview that suggests amyloid-like structure formation as a common phenomenon for disease progression and pathogenesis in multiple syndromes. The review is devoted to providing readers with a broad knowledge of the structure, mode of formation, propagation, and transmission of different extracellular amyloids and their implications in the pathogenesis of diseases. We strongly believe a review on this topic is urgently required to create awareness about the understanding of the fundamental molecular mechanism behind the origin of diseases from an amyloid perspective and possibly look for a common therapeutic strategy for the treatment of these maladies by designing generic amyloid inhibitors.

Aromaticity at position 39 in α-synuclein: A modulator of amyloid fibril assembly and membrane-bound conformations

Recent studies revealed that molecular events related with the physiology and pathology of αS might be regulated by specific sequence motifs in the primary sequence of αS. The importance of individual residues in these motifs remains an important open avenue of investigation. In this work, we have addressed the structural details related to the amyloid fibril assembly and lipid-binding features of αS through the design of site-directed mutants at position 39 of the protein and their study by in vitro and in vivo assays. We demonstrated that aromaticity at position 39 of αS primary sequence influences strongly the aggregation properties and the membrane-bound conformations of the protein, molecular features that might have important repercussions for the function and dysfunction of αS. Considering that aggregation and membrane damage is an important driver of cellular toxicity in amyloid diseases, future work is needed to link our findings with studies based on toxicity and neuronal cell death. BRIEF STATEMENT OUTLINING SIGNIFICANCE: Modulation by distinct sequential motifs and specific residues of αS on its physiological and pathological states is an active area of research. Here, we demonstrated that aromaticity at position 39 of αS modulates the membrane-bound conformations of the protein, whereas removal of aromatic functionality at position 39 reduces strongly the amyloid assembly in vitro and in vivo. Our study provides new evidence for the modulation of molecular events related with the physiology and pathology of αS.

Characterization of a Novel Monoclonal Antibody for Serine-129 Phosphorylated α-Synuclein: A Potential Application for Clinical and Basic Research

The Lewy bodies (LBs) are the pathological hallmark of Parkinson's disease (PD). More than 90% of α-synuclein (α-syn) within LBs is phosphorylated at the serine-129 residue [pSer129 α-syn (p-α-syn)]. Although various studies have revealed that this abnormally elevated p-α-syn acts as a pathological biomarker and is involved in the pathogenic process of PD, the exact pathophysiological mechanisms of p-α-syn are still not fully understood. Therefore, the development of specific and reliable tools for p-α-syn detection is important. In this study, we generated a novel p-α-syn mouse monoclonal antibody (C140S) using hybridoma technology. To further identify the characteristics of C140S, we performed several in vitro assays using recombinant proteins, along with ex vivo assays utilizing the brains of Thy1-SNCA transgenic (Tg) mice, the preformed fibril (PFF)-treated neurons, and the brain sections of patients with PD. Our C140S specifically recognized human and mouse p-α-syn proteins both in vitro and ex vivo, and similar to commercial p-α-syn antibodies, the C140S detected higher levels of p-α-syn in the midbrain of the Tg mice. Using immunogold electron microscopy, these p-α-syn particles were partly deposited in the cytoplasm and colocalized with the outer mitochondrial membrane. In addition, the C140S recognized p-α-syn pathologies in the PFF-treated neurons and the amygdala of patients with PD. Overall, the C140S antibody was a specific and potential research tool in the detection and mechanistic studies of pathogenic p-α-syn in PD and related synucleinopathies.

Altered ceramide metabolism is a feature in the extracellular vesicle-mediated spread of alpha-synuclein in Lewy body disorders

Mutations in glucocerebrosidase (GBA) are the most prevalent genetic risk factor for Lewy body disorders (LBD)-collectively Parkinson's disease, Parkinson's disease dementia and dementia with Lewy bodies. Despite this genetic association, it remains unclear how GBA mutations increase susceptibility to develop LBD. We investigated relationships between LBD-specific glucocerebrosidase deficits, GBA-related pathways, and α-synuclein levels in brain tissue from LBD and controls, with and without GBA mutations. We show that LBD is characterised by altered sphingolipid metabolism with prominent elevation of ceramide species, regardless of GBA mutations. Since extracellular vesicles (EV) could be involved in LBD pathogenesis by spreading disease-linked lipids and proteins, we investigated EV derived from post-mortem cerebrospinal fluid (CSF) and brain tissue from GBA mutation carriers and non-carriers. EV purified from LBD CSF and frontal cortex were heavily loaded with ceramides and neurodegeneration-linked proteins including alpha-synuclein and tau. Our in vitro studies demonstrate that LBD EV constitute a "pathological package" capable of inducing aggregation of wild-type alpha-synuclein, mediated through a combination of alpha-synuclein-ceramide interaction and the presence of pathological forms of alpha-synuclein. Together, our findings indicate that abnormalities in ceramide metabolism are a feature of LBD, constituting a promising source of biomarkers, and that GBA mutations likely accelerate the pathological process occurring in sporadic LBD through endolysosomal deficiency.

Function, Regulation, and Dysfunction of Intrinsically Disordered Proteins

The discovery that a considerable fraction of the eukaryotic proteins lacks a well-defined three-dimensional structure in their native state has revolutionised our general understanding of proteins [...].

Synergistic Effects of Milk-Derived Exosomes and Galactose on α-Synuclein Pathology in Parkinson's Disease and Type 2 Diabetes Mellitus

Epidemiological studies associate milk consumption with an increased risk of Parkinson's disease (PD) and type 2 diabetes mellitus (T2D). PD is an α-synucleinopathy associated with mitochondrial dysfunction, oxidative stress, deficient lysosomal clearance of α-synuclein (α-syn) and aggregation of misfolded α-syn. In T2D, α-syn promotes co-aggregation with islet amyloid polypeptide in pancreatic β-cells. Prion-like vagal nerve-mediated propagation of exosomal α-syn from the gut to the brain and pancreatic islets apparently link both pathologies. Exosomes are critical transmitters of α-syn from cell to cell especially under conditions of compromised autophagy. This review provides translational evidence that milk exosomes (MEX) disturb α-syn homeostasis. MEX are taken up by intestinal epithelial cells and accumulate in the brain after oral administration to mice. The potential uptake of MEX miRNA-148a and miRNA-21 by enteroendocrine cells in the gut, dopaminergic neurons in substantia nigra and pancreatic β-cells may enhance miRNA-148a/DNMT1-dependent overexpression of α-syn and impair miRNA-148a/PPARGC1A- and miRNA-21/LAMP2A-dependent autophagy driving both diseases. MiRNA-148a- and galactose-induced mitochondrial oxidative stress activate c-Abl-mediated aggregation of α-syn which is exported by exosome release. Via the vagal nerve and/or systemic exosomes, toxic α-syn may spread to dopaminergic neurons and pancreatic β-cells linking the pathogenesis of PD and T2D.