Biology subjects

Faravelli, S.

Publications and source records attributed to Faravelli, S..

5 recordsLinked to original sources

bioRxiv2026

Extracellular chaperones modulate AL light chains fibrillar aggregation and contribute to amyloid structural heterogeneity

In AL amyloidosis, monoclonal immunoglobulin light chains (LCs) aggregate as amyloid fibrils in tissues. In synergy with the intrinsic aggregation propensity of specific LC sequences, microenvironment factors may be involved in tuning the disease pathophysiology, in particular proteolytic LC remodelling and heterotypic interactions in the extracellular milieu. Accounting for extrinsic modulators is critical for understanding the phenotypic variability of AL, usually imputed mainly to the LC diversity. We investigated the effects of apolipoprotein E (allele 3, apoE3) and clusterin (CLU), two amyloid-signature proteins involved in extracellular proteostasis, on the fibrillogenesis kinetics of amyloidogenic LC fragments from patient-derived sequences, as well as on aggregate composition, fibril morphology and thermodynamic stability. We show that apoE3 and CLU act as heterotypic interactors of prefibrillar and fibrillar LCs, significantly modulating LC amyloidogenesis, with complex and non-monotypic effects that range from anti- to pro-amyloidogenic depending on their concentration and on the LCs intrinsic amyloidogenicity. ApoE3 and CLU also influence fibril morphology, possibly by modifying protofilament association, and alter their thermodynamic properties. LC interactors may play a significant and insofar underappreciated role in the AL pathophysiology in vivo, likely contributing to phenotypic variability and structural polymorphisms and, possibly, to fibril resilience to amyloid reabsorption strategies.

biochemistry↗

bioRxiv2021

SARS-CoV-2 Spike Affinity and Dynamics Exclude the Strict Requirement of an Intermediate Host

SARS-CoV-2 proximal origin is still unclear, limiting the possibility of foreseeing other spillover events with pandemic potential. Here we propose an evolutionary model based on the thorough dissection of SARS-CoV-2 and RaTG13 - the closest bat relative - spike dynamics, kinetics and binding to ACE2. Our results indicate that both spikes share nearly identical, high affinities for Rhinolophus affinis bat and human ACE2, pointing out to negligible species barriers directly related to receptor binding. Also, SARS-CoV-2 spike shows a higher degree of dynamics and kinetics optimization that favors ACE2 engagement. Therefore, we devise an affinity-independent evolutionary process that likely took place in R. affinis bats and limits the eventual involvement of other animal species in initiating the pandemic to the role of vector.

microbiology↗

bioRxiv2020

NT-mini, a recombinant tool for the study of Neurotrypsin functionality

Neurotrypsin (NT) is a highly specific nervous system multi-domain serine-protease best known for its selective processing of the potent synaptic organiser agrin. Its enzymatic activity is thought to influence processes of synaptic plasticity, with its deregulation causing accelerated neuromuscular junction (NMJ) degeneration or contributing to forms of mental retardation. Something which, based on the available literature, likely stems from NT-based regulation of agrin signalling. However, dissecting the exact biological implications of NT-agrin interplay is difficult, owing to the scarce molecular detail regarding NT activity and NT-agrin interactions. The difficult recombinant production of NT in its catalytically competent form is at the base of these limitations, and is currently constraining a more detailed molecular, biochemical and structural characterisation of the NT-agrin system. We have developed a novel strategy to reliably produce and purify a truncated but catalytically competent variant of NT called NT-mini. The characterisation of our construct highlighted almost wild type-like behaviour with comparable specificity, and conservation of modulation by calcium and heparin despite the lack of several accessory domains. With the data obtained from NT-mini it was then possible to identify NTs heparin-binding domain, and discover a novel putative Zinc-based modulation of NT. Additionally, NT-mini allowed us to investigate the effect of NT activity on myotube formation in controlled cell-based experiments, evidencing a negative impact on myoblast fusion dependant on enzymatic activity. Collectively, this shows the viability of NT-mini as a model to study NT functionality, allowing to expand both in-vitro and "in-cellulo" investigations and providing a foundation to unravel the molecular underpinnings and biological significance of NT-agrin interactions.

biochemistry↗

bioRxiv2020

Gene families with stochastic exclusive gene choice underlie cell adhesion in mammalian cells

Exclusive stochastic gene choice combines precision with diversity. This regulation enables most T-cells to express exactly one T-cell receptor isoform chosen from a large repertoire, and to react precisely against diverse antigens. Some cells express two receptor isoforms, revealing the stochastic nature of this process. A similar regulation of odorant receptors and protocadherins enable cells to recognize odors and confer individuality to cells in neuronal interaction networks, respectively. We explored whether genes in other families are expressed exclusively by analyzing single cell RNA-seq data with a simple metric. Chromosomal segments and families are more likely to express genes concurrently than exclusively, possibly due to the evolutionary and biophysical aspects of shared regulation. Nonetheless, gene families with exclusive gene choice were detected in multiple cell types, most of them are membrane proteins involved in ion transport and cell adhesion, suggesting the coordination of these two functions. Thus, stochastic exclusive expression extends beyond the prototypical families, permitting precision in gene choice to be combined with the diversity of intercellular interactions.

bioinformatics↗

bioRxiv2019

A cooperative network of molecular "hot spots" highlights the complexity of LH3 collagen glycosyltransferase activities

Hydroxylysine glycosylations are collagen-specific post-translational modifications essential for maturation and homeostasis of fibrillar as well as non-fibrillar collagen molecules. Lysyl hydroxylase 3 (LH3) is the only human enzyme capable of performing two chemically-distinct collagen glycosyltransferase reactions using the same catalytic site: inverting beta-1,O-galactosylation of hydroxylysines and retaining alpha-1,2-glycosylation of galactosyl hydroxylysines. Here, we used structure-based mutagenesis to show that both glycosyltransferase activities are strongly dependent on a broad cooperative network of amino acid side chains which includes the first-shell environment of the glycosyltransferase catalytic site and shares features with both retaining and inverting enzymes. We identified critical "hot spots" leading to selective loss of inverting activity without affecting the retaining reaction. Finally, we present molecular structures of LH3 in complex with UDP-sugar analogs which provide the first structural templates for LH3 glycosyltransferase inhibitor development. Collectively, our data provide a comprehensive overview of the complex network of shapes, charges and interactions that enable LH3 glycosyltransferase activities, expanding the molecular framework for the manipulation of glycosyltransferase functions in biomedical and biotechnological applications.

biochemistry↗