Biology subjects

Melo, A. A.

Publications and source records attributed to Melo, A. A..

9 recordsLinked to original sources

bioRxiv2026

Cryo-EM Structures of Infectious Low-Twist α-Synuclein Filaments in Lewy Bodies

-Synuclein (aSyn) aggregation within Lewy bodies underlies Parkinson's disease and associated dementias. These aggregates are often comprised of amyloid filaments, most of which appear untwisted or have extremely low twist, complicating high-resolution structural determination by cryogenic electron microscopy (cryo-EM). Here, we isolated filaments from the brain tissue of a patient with dementia with Lewy bodies and show infectivity in a cell line system that propagates Lewy aSyn. Then, we determined 2.3-2.9 [A] cryo-EM structures of low-twist aSyn filaments from this tissue and from a publicly available Parkinson's disease dementia dataset. In both structures, the protofilament adopts a fold highly similar to the canonical Lewy fold with conserved cofactor and peptidic densities. Compared to previously resolved high-twist filaments, the low-twist filament is left-handed and flattened along the filament axis, resulting in register shifts of interlayer contacts, while preserving the overall architecture. Our results establish that low-twist filaments, which include over 75% of disease-associated Lewy aSyn amyloids, share a common structural core with high-twist forms and are the predominant aSyn species in samples that engage in templated infection.

biophysics↗

bioRxiv2026

Adaptation of α-synuclein fibrils following multiple system atrophy transmission to mice

Synucleinopathies are a group of neurodegenerative diseases characterized by the presence of misfolded -synuclein inclusions which cause progressive disease by spreading throughout the brain in a prion-like manner. Throughout the neurodegenerative disease field, the ability of a single protein to give rise to multiple distinct clinical disorders is explained by the strain hypothesis, or the idea that the misfolded protein conformation determines the resulting disease. This was initially shown using transmission studies in cell lines and mouse models; more recently cryo-electron microscopy (cryo-EM) validated this idea by identifying distinct -synuclein filament folds in brain tissues from patients with Parkinsons disease, multiple system atrophy (MSA), and juvenile-onset synucleinopathy. However, very little is known about the -synuclein filament structures that form in animal models of these disorders, and thus their relevance to human disease and suitability as models for therapeutic development remains a question. Here we report the first atomic resolution cryo-EM structures of -synuclein fibrils from an MSA patient sample before and after transmission to a transgenic mouse model of disease. Our findings indicate that while distinct adaptations occur during fibril replication in the mouse host, key structural facets are maintained, validating the merits of this transmission model for supporting preclinical research on MSA.

neuroscience↗

bioRxiv2026

Distinct tau filament folds in familial frontotemporal dementia due to the MAPT S305I mutation

Frontotemporal lobar degeneration with tau inclusions (FTLD-tau) comprise a class of fatal heterogeneous neurodegenerative diseases. Approximately 10% arise from pathogenic MAPT mutations and often cause severe, early-onset disease with pathology that is distinct yet partially overlapping with sporadic cases. Here, we evaluated post-mortem tissue from a patient with FTLD-tau due to MAPT S305I showing neuropathology most consistent with argyrophilic grain disease (AGD), a prevalent limbic tauopathy of aging. Structures determined by cryo-electron microscopy reveal tau filament folds that differ from those found in sporadic AGD or other tauopathies and feature a 4-layer architecture stabilized by the Ile substitution within its core. Comparative structural analysis reveals conserved motifs are shared among AGD, corticobasal degeneration, and MAPT P301T. A well-defined density stacks along a cationic cleft, indicative of a bound RNA-like polyanion or small-molecule. In vitro analysis shows the S305I mutation promotes fibrilization relative to normal tau. These results demonstrate that MAPT S305I stabilizes a distinct aggregation-prone tau fold that likely contributes to disease pathology and heterogeneity beyond its known splicing defects, and underscore potential limitations of using the most pathologically similar genetic form as a model for sporadic FTLD-tau.

neuroscience↗

bioRxiv2025

De novo design of semisynthetic protein nanopores

Protein nanopores are essential components of single-molecule oligonucleotide sequencing and sensing devices. Here, we demonstrate that installing additional de novo subunits enables large-scale architectural changes of nanopore complexes. We design de novo proteins that integrate seamlessly with the CsgG pore to form 18-subunit, 315-kilodalton complexes with precisely sculpted pore architectures and tailored ion conduction, opening new possibilities for engineering enhanced nanopores with customized structural and functional properties.

biochemistry↗

bioRxiv2025

Structure-specific Mini-Prion Model for Alzheimer's Disease Tau Fibrils

A critical discovery of the past decade is that tau protein fibrils adopt disease-specific hallmark structures in each tauopathy. The faithful generation of synthetic fibrils adopting hallmark structures that can serve as targets for developing diagnostic and/or therapeutic strategies remains a grand challenge. We report on a rational design of synthetic fibrils built of a short peptide that adopts a critical structural motif in tauopathy fibrils found in Alzheimers Disease (AD) and Chronic Traumatic Encephalopathy (CTE). They serve as minimal prions with exquisite seeding competency, in vitro and in tau biosensor cells, for recruiting tau constructs ten times larger its size en route to AD or CTE fibril structures. We demonstrate that the generation of AD and CTE-like fibril structures is dramatically catalyzed in the presence of mini-AD prions and further influenced by salt composition in solution. Double Electron-Electron Resonance studies confirmed the preservation of AD-like folds across multi-generational seeding. Fibrils formed with the full AD/CTE-like core show strong seeding competency, with their templating effect dominating over the choice of salt composition that tunes the initial selection of AD- and CTE-like fibril populations. The mini-AD prions serve as a potent catalyst with templating capabilities that offer a novel strategy to design pathological tau fibril models.

biophysics↗

bioRxiv2024

Structure of a novel α-synuclein filament fold from multiple system atrophy

Multiple system atrophy (MSA) is a synucleinopathy, a group of related diseases characterized by the accumulation of -synuclein aggregates in the brain. In MSA, these aggregates form glial cytoplasmic inclusions, which contain abundant cross-{beta} amyloid filaments. Structures of -synuclein filaments isolated from MSA patient tissue were determined by cryo-electron microscopy (cryo-EM), revealing three discrete folds that are distinct from -synuclein filaments associated with other synucleinopathies. Here, we use cryo-EM classification methods to characterize filaments from one individual with MSA and identify a novel, low-populated MSA filament fold (designated Type I2) in addition to a predominant class comprising MSA Type II2. The 3.3-[A] resolution structure of the Type I2 filament reveals a fold consisting of two asymmetric protofilaments. One is identical to a previously solved Type I protofilament, while the second adopts a novel fold that is chimeric between two previously reported Type I and II protofilaments. These results further define disease-specific folds of -synuclein filaments that develop in MSA and have implications for the design of therapeutic and diagnostic molecules that target disease.

biophysics↗

bioRxiv2021

Cryo-electron tomography reveals structural insights into the membrane binding and remodeling activity of dynamin-like EHDs

Dynamin-related Eps15-homology domain containing proteins (EHDs) oligomerize on membrane surfaces into filaments leading to membrane remodeling. EHD crystal structures in an open and a closed conformation were previously reported, but structural information on the membrane-bound EHD oligomeric structure has remained enigmatic. Consequently, mechanistic insight into EHD-mediated membrane remodeling is lacking. Here, by using cryo-electron tomography and subtomogram averaging, we determined the structure of an EHD4 filament on a tubular membrane template at an average resolution of 7.6 [A]. Assembly of EHD4 is mediated via interfaces in the G-domain and the helical domain. The oligomerized EHD4 structure resembles the closed conformation, where the tips of the helical domains protrude into the membrane. The variation in filament geometry and tube radius suggests the AMPPNP-bound filament has a spontaneous curvature of approximately 1/70 nm-1. Combining the available structural and functional data, we propose a model of EHD-mediated membrane remodeling.

biophysics↗

bioRxiv2020

Photocatalytic plant LPOR forms helical lattices that shape membranes for chlorophyll synthesis

Chlorophyll (Chl) biosynthesis, crucial to life on Earth, is tightly regulated because its precursors are phototoxic1. In flowering plants, the enzyme Light-dependent Protochlorophyllide OxidoReductase (LPOR) captures photons to catalyze the penultimate reaction: the reduction of a double-bond within protochlorophyllide (Pchlide) to generate chlorophyllide (Chlide)2,3. In darkness, LPOR oligomerizes to facilitate photon energy transfer and catalysis4,5. However, the complete 3D structure of LPOR, the higher-order architecture of LPOR oligomers, and the implications of these self-assembled states for catalysis, including how LPOR positions Pchlide and the cofactor NADPH, remain unknown. Here we report the atomic structure of LPOR assemblies by electron cryo-microscopy (cryoEM). LPOR polymerizes with its substrates into helical filaments around constricted lipid bilayer tubes. Portions of LPOR and Pchlide insert into the outer membrane leaflet, targeting the product, Chlide, to the membrane for the final reaction site of chlorophyll biosynthesis. In addition to its crucial photocatalytic role, we show that in darkness LPOR filaments directly shape membranes into high-curvature tubules with the spectral properties of the prolammelar body, whose light-triggered disassembly provides lipids for thylakoid assembly. Our structure of the catalytic site, moreover, challenges previously proposed reaction mechanisms6. Together, our results reveal a new and unexpected synergy between photosynthetic membrane biogenesis and chlorophyll synthesis in plants orchestrated by LPOR.

biophysics↗

bioRxiv2019

EHD2-mediated restriction of caveolar dynamics regulates cellular lipid uptake

Eps15-homology domain containing protein 2 (EHD2) is a dynamin-related ATPase located at the neck of caveolae, but its physiological function has remained unclear. We found that global genetic ablation of EHD2 in mice led to increased fat deposits in several organs. This organismic phenotype was paralleled at the cellular level by an increased lipid uptake via a CD36-dependent pathway, an elevated number of detached caveolae and higher caveolar mobility. Following a high fat diet, various enzymes involved in de novo fatty acid synthesis were down-regulated in EHD2 KO mice. Furthermore, EHD2 expression itself was down-regulated in the visceral fat of two obese mouse models and in diet-induced obesity. Thus, EHD2 controls a cell-autonomous, caveolae-dependent lipid uptake pathway, implicating a role of EHD2 in fat accumulation and obesity.

cell biology↗