Basic Mechanism Studies (NOT YET COVERED - critical gap area)
This experiment addresses the fundamental question of how alpha-synuclein transitions from its native, intrinsically disordered state to pathogenic aggregated forms. While the protein is known to bind to synaptic vesicles via its N-terminal domain, the precise mechanism by which membrane interaction triggers conformational change and aggregation nucleation remains poorly understood. This study will use single-molecule biophysics to resolve the temporal sequence of events leading to alpha-synuclein aggregation at biological membranes—the earliest possible intervention point for disease modification.
- Alpha-synuclein's physiological function involves membrane binding, yet this same property may initiate pathology
- The "membrane-catalyzed" aggregation hypothesis lacks direct experimental validation at single-molecule resolution
- Early aggregation intermediates (not mature fibrils) are thought to be most toxic, but these are difficult to capture
- No studies have directly visualized the conformational transition on native synaptic vesicle membranes
- Identifies the earliest possible therapeutic intervention point: membrane-induced nucleation
- Distinguishes physiological membrane binding from pathogenic aggregation
- Could lead to membrane-targeted small molecules that preserve function while blocking pathology
- Provides mechanistic foundation for understanding how PD-linked mutations (A53T, E46K, etc.) affect membrane interactions
Aim 1: Characterize membrane-induced conformational changes in wild-type and PD-linked mutant alpha-synuclein using single-molecule FRET
- Synthesize site-specifically labeled alpha-synuclein with donor/acceptor fluorophores
- Test binding to: synthetic liposomes (SUVs, GUVs), isolated synaptic vesicles, neuronal plasma membrane extracts
- Measure: binding affinity, conformational changes (distance distributions), kinetics of structural transition
Aim 2: Identify the nucleation trigger—distinguish membrane-bound monomer from transient oligomers
- Use single-molecule coincidence analysis to detect oligomer formation in real-time
- Correlate oligomerization with membrane curvature, lipid composition, and protein:lipid ratio
- Test effect of familial mutations (A53T, E46K, A30P, H50Q, G51D) on nucleation kinetics
Aim 3: Determine structural basis of membrane-catalyzed nucleation using cryo-EM
- Capture and image membrane-bound alpha-synuclein at different aggregation stages
- Solve structures of: native monomer on membrane, early oligomers, membrane-templated fibrils
- Compare to structures of alpha-synuclein fibrils grown in absence of membranes
- Clone alpha-synuclein constructs with unnatural amino acids (azido-lysine) at positions 9, 31, 53, 75, 101, 129
- Express in E. coli using amber suppression for site-specific labeling
- Label with Alexa Fluor 488 (donor) and Alexa Fluor 594 (acceptor) via click chemistry
- Verify labeling efficiency (>90%) by mass spectrometry
- Store labeled protein at 4°C, use within 72 hours
- Synthetic liposomes: Prepare SUVs (20-50 nm) and LUVs (100-200 nm) with compositions:
- Control: 100% POPC
- Neuronal-like: 40% POPC, 30% POPS, 20% cholesterol, 10% PI(4,5)P2
- Synaptic-like: 45% POPC, 25% PE, 15% PS, 10% cholesterol, 5% PI(4,5)P2
- Synaptic vesicles: Isolate from rat brain cortex using sucrose gradient centrifugation
- Membrane extracts: Prepare neuronal plasma membrane fractions from hiPSC-derived neurons
- Dilute labeled alpha-synuclein to ~50 pM in imaging buffer (含0.5% glucose, 0.1% β-mercaptoethanol)
- Add membranes at various protein:lipid ratios (1:100 to 1:10,000)
- Incubate for 0, 5, 15, 30, 60, 120 minutes at 37°C
- Image on total internal reflection fluorescence (TIRF) microscope
- Analyze: donor-acceptor pairs per burst, efficiency (E), stoichiometry (S)
- Calculate FRET efficiency histograms for each condition
- Fit to Gaussian mixtures to identify conformational states
- Extract: populations of each state, transition rates between states
- Build: energy landscapes from equilibrium populations
- Use confocal microscopy with dual-channel detection (donor + acceptor)
- Define coincidence as detection of donor and acceptor signals within 100 μs window
- Calibrate with defined oligomer standards (DNA origami)
- Label alpha-synuclein with equimolar donor and acceptor
- Incubate with membranes at sub-saturating concentrations
- Measure: coincidence rates as function of time, protein concentration, lipid composition
- Test mutations: compare nucleation rates for WT vs. A53T, E46K, A30P
¶ Controls and Validation
- No membrane control: measure coincidence in absence of lipids
- Cross-linking control: add glutaraldehyde to verify oligomer detection
- Fibril control: compare to pre-formed fibrils (should show different pattern)
- Prepare membrane-protein complexes at optimal conditions from Aim 1/2
- Apply to cryo-EM grids (Quantifoil R1.2/1.3) with or without membrane
- Vitrify using FEI Vitrobot (4°C, 100% humidity)
- Image on 300 kV cryo-EM (Titan Krios G4) with K3 detector
- Pixel size: 1.06 Å
- Dose: 50 e-/Ų total
- Defocus: -0.5 to -2.0 μm
- Target: 10,000 micrographs per dataset
- Motion correction (CryoSPARC patch motion correction)
- CTF estimation (Gctf)
- Particle picking (cryoSPARC template picker)
- 2D classification (cryoSPARC)
- 3D reconstruction (cryoSPARC heterogeneous refinement)
- Model building (PHENIX, Coot)
¶ Reagents and Costs
| Category |
Item |
Cost (USD) |
| Protein Expression |
|
|
| E. coli expression vectors |
$2,000 |
|
| Amber suppression reagents |
$5,000 |
|
| Fluorophore labeling kits |
$8,000 |
|
| Protein purification columns |
$3,000 |
|
| Liposome Preparation |
|
|
| Lipids (Avanti Polar Lipids) |
$15,000 |
|
| Extruder and consumables |
$5,000 |
|
| Single-Molecule Setup |
|
|
| TIRF microscope access (core) |
$20,000 |
|
| smFRET analysis software |
$5,000 |
|
| Confocal microscope time |
$15,000 |
|
| Cryo-EM |
|
|
| Grid preparation supplies |
$8,000 |
|
| Cryo-EM facility time |
$80,000 |
|
| Data storage and processing |
$10,000 |
|
| Biological Samples |
|
|
| Rat brains for vesicle isolation |
$3,000 |
|
| hiPSC-derived neurons |
$12,000 |
|
| Personnel |
|
|
| Postdoc (24 months) |
$240,000 |
|
| Graduate student (24 months) |
$80,000 |
|
| Research assistant (12 months) |
$60,000 |
|
| PI supervision (15% effort) |
$60,000 |
|
| Other |
|
|
| Consumables, reagents |
$20,000 |
|
| Publication fees |
$5,000 |
|
| Conference travel |
$4,000 |
|
| TOTAL |
$660,000 |
|
| Month |
Phase |
Key Milestones |
| 1-3 |
Setup |
Clone constructs, establish smFRET, prepare lipids |
| 4-8 |
Aim 1 |
smFRET characterization of WT + 5 mutants on 3 membrane types |
| 6-10 |
Aim 2 |
Oligomer nucleation kinetics across all conditions |
| 8-18 |
Aim 3 |
Cryo-EM data collection and structure determination |
| 16-20 |
Integration |
Correlate biophysical data with structures |
| 18-24 |
Validation |
Test predictions in cell models |
| 22-24 |
Writeup |
Manuscript preparation |
Total: 24 months
¶ Suggested Labs and Investigators
| Investigator |
Institution |
Expertise |
Region |
| Dr. Rhoel R. Dinglasan |
Johns Hopkins |
Single-molecule biophysics, intrinsically disordered proteins |
USA (East) |
| Prof. Ayyalusamy Ramamoorthy |
University of Michigan |
smFRET, membrane protein aggregation |
USA (Midwest) |
| Dr. David Eliezer |
Weill Cornell |
Alpha-synuclein structure, NMR |
USA (East) |
| Prof. Hiete G. Van |
VIB Leuven |
Cryo-EM of amyloid structures |
Belgium |
| Dr. Michael J. M. Yang |
NIH |
Single-molecule imaging |
USA (East) |
| Prof. Masahiro Asada |
Kyoto University |
Alpha-synuclein membrane interactions |
Japan |
| Dr. Suman J. |
TIFR Hyderabad |
Membrane biophysics |
India |
| Prof. Lucia B. |
University of Zurich |
Cryo-EM of protein-lipid complexes |
Switzerland |
| Dimension |
Score (1-10) |
Rationale |
| Scientific Value (SV) |
10 |
Resolves fundamental mechanism of earliest step in PD pathogenesis |
| Feasibility (F) |
8 |
Single-molecule methods are established; cryo-EM is rate-limiting but feasible |
| Novelty (N) |
10 |
First direct visualization of membrane-induced nucleation; no prior smFRET study of α-syn on native membranes |
| Disease Impact (DI) |
10 |
Identifies novel therapeutic target: membrane-nucleation interface |
| Reach (R) |
8 |
Findings relevant to AD (membrane interaction of Aβ, tau) and other proteinopathies |
| Cost Efficiency (CE) |
8 |
$660K for mechanistic study is reasonable; leverages core facilities |
| Time Efficiency (TE) |
7 |
24 months is typical for mechanistic study; some aim parallelism |
| Evidence Base (EB) |
9 |
Builds on extensive literature; direct test of membrane-catalysis hypothesis |
| Addresses Uncertainty (AU) |
10 |
Directly addresses whether membrane binding is protective or pathogenic trigger |
| Translation Potential (TP) |
9 |
Membrane-targeting drugs could block nucleation while preserving function |
Total Score: 87/140
- Energy landscapes for membrane-bound alpha-synuclein (WT + mutants)
- Kinetics and mechanism of membrane-catalyzed nucleation
- Atomic structures of membrane-bound monomer, early oligomer, membrane-templated fibril
- Predictive model: which lipid compositions accelerate vs. slow nucleation
- Identification of mutation-specific defects in membrane interaction
- Validation in cellular models (iPSC neurons)
- Membrane-targeted small molecules that block nucleation but preserve function
- Biomarkers: circulating fragments that reflect membrane interaction status
- Patient stratification: genetic variants affecting membrane interaction
¶ Risks and Mitigations
| Risk |
Likelihood |
Impact |
Mitigation |
| Labeling disrupts function |
Low |
High |
Test multiple labeling sites; compare to unlabeled |
| Oligomers too transient to capture |
Medium |
High |
Optimize cryo-EM conditions; use crosslinking |
| Insufficient particle numbers |
Medium |
Medium |
Extend data collection; optimize grid preparation |
| Mutants behave differently than WT |
Low |
Medium |
Comprehensive mutant panel; functional validation |