Biology subjects

Yan, N. L.

Publications and source records attributed to Yan, N. L..

4 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

Resolving the Activation Mechanism of the Human 20S Proteasome

Proteasome activators (PAs) bind the -subunits of the human 20S proteasome (h20S), opening the "gates" and allowing entry of substrate proteins. Aging is associated with diminished proteasome activity, leading to interest in understanding this activation mechanism. Evolving models have been proposed regarding PAs C-terminal tails, yet the critical molecular contacts for gate-opening are unclear. Here, we show a conserved leucine in the 5th position (P5) of the C-terminus is essential for h20S gate opening. By engineering C-termini in a model activator, PA26E102A, we show mutations to P5 systematically modulate proteasome activity in vitro and in cells. Structures of PA26E102A:h20S complexes at 2.7-3.2 [A] resolution identify interactions between P5 and a conserved arginine in the h20S, leading to partial or full gate opening. These results clarify the essential contacts required for h20S gate opening, potentially enabling design of proteasome activation therapies.

biophysics↗

bioRxiv2026

Small molecule stabilization of diverse amyloidogenic immunoglobulin light chains revealed by hydrogen-deuterium exchange mass spectrometry

Immunoglobulin light chains, a component of antibodies, can misfold and aggregate to cause systemic AL amyloidosis. Aggregation, including amyloid fibril formation, requires unfolding of the full-length light chain from its native state, and in most cases aberrant proteolysis. Small molecules that bind to the native state of light chains to stabilize them against conformational excursions and proteolysis are under development as drug candidates for AL amyloidosis. Since each patient has a unique light chain sequence, a challenge for candidate stabilizer drugs is to bind multiple light chains and suppress their dynamics. Here, we used hydrogen-deuterium exchange measured by mass spectrometry to characterize the binding of six small molecule stabilizers to eleven different {lambda} light chain proteins. Despite structural and dynamic differences among the light chains, the binding of the most efficacious stabilizer molecule led to increased protection from hydrogen exchange, consistent with reduced local and global unfolding. Protection upon binding was most prominent in residues within complementarity determining region 3 and framework region 4 of the light chain variable domains, which undergo major conformational changes enabling amyloid formation. Stabilizer binding also reduced the rate at which all light chains were cleaved by protease. These data show that these stabilizers suppress the range of conformational dynamics associated with light chain aggregation, supporting their therapeutic potential. HighlightsO_LISmall-molecule kinetic stabilizers suppress conformational dynamics and aberrant proteolysis of diverse amyloidogenic full-length {lambda} light chains. C_LIO_LIHDX-MS indicates conserved protection in regions forming the interface between the two variable domains of the light chain dimer, corresponding to residues that form the core of patient-derived amyloid fibrils. C_LIO_LIPLIMSTEX binding titrations show coupled binding, dimerization and stabilization at sub-micromolar kinetic stabilizer concentrations. C_LIO_LISmall molecule kinetic stabilization across different {lambda} sequences supports kinetic stabilizers as a promising therapeutic strategy for AL amyloidosis. C_LI

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↗