Speculative Grant Proposal: Cloning the Lichen Prion-Degrading Serine Protease and Testing Its Efficacy in a PrP^Sc–Mediated Chronic Pain Model
Cloning the Lichen Prion-Degrading Serine Protease and Testing Its Efficacy in a PrP^Sc–Mediated Chronic Pain Model
Proposed Funding Mechanism: NIH R01 / DoD PRMRP / CURE / PCBI
Duration: 5 Years
Total Direct Costs (estimated): ~$2,500,000 USD
Abstract
PrP^C is an endogenous inhibitor of NMDA receptor signaling in the spinal dorsal horn, and its loss or dysfunction drives central sensitization in chronic pain states (Gadotti & Zamponi, 2011). We hypothesize that after peripheral nerve injury (e.g., surgery, trauma), misfolded, β-sheet-rich PrP (PrP^C-like) accumulates at axon terminals and/or within synaptic compartments, sequestering functional PrP^C and producing a local functional knockout — disinhibiting NMDA receptors and triggering chronic regional pain.
A serine protease of fungal origin, found in ~50% of tested lichen species (Johnson et al., 2011; 2012; Rodriguez et al., 2012), has been shown to degrade PrP^Sc β-sheets by ≥2 logs in vitro. However, the enzyme has never been cloned, sequenced, or recombinantly expressed. This proposal outlines a complete pipeline to: (1) identify and clone the lichen serine protease gene from Parmelia sulcata; (2) recombinantly express and purify the active enzyme; (3) characterize its kinetics against PrP^Sc from multiple mammalian species; and (4) test its ability to reverse PrP^Sc-mediated chronic pain in a newly developed CRPS rodent model.
If successful, this work will yield the first targeted biological tool for degrading β-sheet PrP aggregates at peripheral nerve endings, opening an entirely new therapeutic axis for chronic regional pain syndromes.
Specific Aims
Aim 1. Identify and Clone the Prion-Degrading Serine Protease Gene from Parmelia sulcata
Rationale: The activity has been confirmed as a serine protease of fungal mycobiont origin (Johnson et al., 2011), but its molecular identity is completely unknown. P. sulcata shows the highest reported activity. No genome sequence is publicly available.
Experimental Plan:
| Step | Method | Expected Outcome |
|---|---|---|
| 1.1 | Collect and axenically culture P. sulcata mycobiont (isolate from algal/bacterial partners) | Pure fungal culture confirmed by ITS barcoding |
| 1.2 | Extract total RNA from culture at timepoints of peak protease activity (assayed by zymography against recombinant PrP^Sc) | RNA-seq library from active cultures |
| 1.3 | Whole-transcriptome sequencing (Illumina NovaSeq 6000, 150 bp paired-end, ~50M reads) | Transcriptome assembly (~15,000–25,000 fungal gene models) |
| 1.4 | Bioinformatic filter for candidate serine proteases: | 20–50 candidate serine protease sequences |
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| 1.5 | Heterologous expression of top 10 candidates in Pichia pastoris (pPICZα vector, methanol-induced) | 10 recombinant secreted proteases |
| 1.6 | High-throughput activity screen: incubate each recombinant protease with proteinase K–resistant PrP^Sc (purified from RML scrapie mouse brain); measure degradation by: | 1 positive hit (or more) — the protease(s) that degrade PrP^Sc |
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Go/No-Go Criteria:
Go: ≥1 candidate clone shows ≥1 log reduction in PrP^Sc signal within 60 min at 25°CNo-Go: No candidate active → revisit transcriptome for missed candidates, consider activity-guided biochemical purification (Aim 1 alternative path)
Alternative Path (if transcriptome mining fails):
If no recombinant candidate shows activity, fall back to classical biochemical purification:
- Acetone precipitation of P. sulcata thallus
- Ion-exchange chromatography (Q Sepharose)
- Size-exclusion chromatography (Superdex 200)
- Activity tracking via zymogram gel
- Mass spectrometry (LC-MS/MS) of active band → peptide fingerprint → degenerate PCR → gene cloning
Aim 2. Recombinant Expression, Purification, and Biochemical Characterization of the Active Enzyme
Rationale: Even a single positive hit requires full characterization to confirm identity and determine suitability for pain model testing.
Experimental Plan:
| Step | Method | Expected Outcome |
|---|---|---|
| 2.1 | Scale-up expression in P. pastoris (5 L fermenter), Ni-NTA purification (His-tagged) | 10–50 mg purified enzyme |
| 2.2 | Biochemical characterization: | Full kinetic profile; confirm serine protease class and subfamily |
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| 2.3 | Substrate specificity: | PrP^Sc degradation kinetics |
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| 2.4 | Structural characterization: | High-resolution structure; active site geometry for rational drug design |
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| 2.5 | Infectivity assay (gold standard) | Definitive proof of prion deactivation |
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Go/No-Go Criteria:
Go: ≥2 log reduction in PrP^Sc within 1 hour AND eliminates infectivity (survival ≥ untreated control)
No-Go: Partial degradation but infectivity retained → reconsider mechanism and suitability for therapeutic use
Aim 3. Develop a CRPS Rodent Model with Demonstrable PrP β-Sheet Accumulation at Peripheral Nerve Endings
Rationale: No existing chronic pain model has been characterized for PrP β-sheet aggregates. This model must be validated first.
Experimental Plan:
| Step | Method | Expected Outcome |
|---|---|---|
| 3.1 | Model selection: chronic constriction injury (CCI) of the sciatic nerve in adult male/female C57BL/6 mice | Established neuropathic pain model, analogous to surgical nerve damage |
| 3.2 | Behavioral phenotyping (days 0–28 post-surgery): | Confirmed chronic pain state |
| Mechanical allodynia (von Frey filaments, up-down method) | ↓ threshold | |
| Thermal hyperalgesia (Hargreaves test) | ↓ latency | |
| Cold allodynia (acetone drop) | ↑ response | |
| Weight bearing asymmetry (incapacitance meter) | ↑ asymmetry | |
| 3.3 | PrP β-sheet detection at axon terminals (the central test of the hypothesis): | |
| A. Immunofluorescence: | PrP co-localized with β-sheet markers | ||
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| B. Biochemical detection: | Quantified PrP^Sc-like material | ||
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| RT-QuIC (Real-Time Quaking-Induced Conversion): | Seeded amplification of β-sheet PrP | ||
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| 3.4 | Correlation analysis: | Dose-response relationship |
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Go/No-Go Criteria:
Go: Go: PK-resistant PrP^Sc detected at sciatic nerve endings of CCI mice, with significant correlation (r ≥ 0.6, p < 0.05) between PrP^Sc amount and pain severity
No-Go: No PrP^Sc detected → hypothesis is wrong at the level of simple aggregation → pivot to testing PrP^C loss mechanism (cellular fractionation, surface biotinylation to quantify end-terminal PrP^C)
Aim 4. Test Lichen Protease as a Therapeutic for PrP β-Sheet–Mediated Chronic Pain
Rationale: The ultimate test of the hypothesis — does degrading PrP β-sheets at peripheral nerve endings reverse chronic pain?
Experimental Plan:
| Step | Method | Expected Outcome |
|---|---|---|
| 4.1 | Dose-finding study: | Optimal dose and route identified |
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| 4.2 | Efficacy study (the main event): | Therapeutic proof-of-concept |
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| 4.3 | Mechanism confirmation: | NMDA receptor link confirmed or refuted |
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| 4.4 | Safety assessment: | No off-target nerve damage |
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Go/No-Go Criteria for Clinical Translation:
Go: ≥50% reversal of mechanical allodynia (von Frey threshold restored to ≥75% of pre-injury baseline), sustained for ≥7 days after last dose, with no significant nerve damage
No-Go: Partial or no effect → consider: (1) wrong mechanism, (2) poor enzyme stability in vivo, (3) insufficient tissue penetration
Timeline
Budget (Estimated Direct Costs)
| Category | Year 1 | Year 2 | Year 3 | Year 4 | Year 5 | Total |
|---|---|---|---|---|---|---|
| Personnel (PI, postdoc, tech, grad) | $180K | $185K | $190K | $196K | $202K | $953K |
| Supplies (molecular biology, protein purification, animal housing) | $75K | $100K | $120K | $100K | $80K | $475K |
| Sequencing (RNA-seq, genome) | $50K | $10K | — | — | — | $60K |
| Mass spectrometry | — | $15K | $5K | — | — | $20K |
| Crystallography/cryo-EM (core fees) | — | — | $40K | $30K | — | $70K |
| Animal purchase and per diem | $10K | $30K | $40K | $40K | $30K | $150K |
| Behavioral equipment (von Frey, Hargreaves) | $25K | — | — | — | — | $25K |
| Publication fees / travel | $5K | $5K | $10K | $10K | $15K | $45K |
| Total Direct | $345K | $345K | $405K | $376K | $327K | $1,798K |
| Indirect (F&A, 55% on-campus) | $190K | $190K | $223K | $207K | $180K | $990K |
| Total | $535K | $535K | $628K | $583K | $507K | $2,788K |
Potential Pitfalls and Mitigations
| Pitfall | Risk | Mitigation |
|---|---|---|
| Enzyme not produced by mycobiont alone — requires algal/bacterial partner | Medium | Metagenomic RNA-seq includes all symbionts; heterologous expression in P. pastoris handles eukaryotic or prokaryotic genes |
| Enzyme is a post-translationally modified complex (glycosylated, requires chaperone) | Medium | Use P. pastoris (glycosylation competent); also try E. coli with refolding; cell-free expression as backup |
| Recombinant enzyme is inactive | High | Include native purification (Aim 1 alternative path) in parallel; co-expression with Kex2 protease to address post-translational processing |
| No PrP^Sc detected in CCI mouse sciatic nerve (Aim 3 fails) | High | Refutes the strong hypothesis but allows testing of PrP^C loss-of-function mechanism; pivot Aim 4 to PrP^C replacement therapy |
| Protease causes nerve damage at injection site | Medium | Tune dose; formulate with controlled-release (PLGA nanoparticles); engineer active-site mutants with reduced off-target proteolysis |
| PrP^Sc is intracellular — protease cannot reach it | Medium | Test cell-penetrating peptide fusion (TAT, penetratin); use liposomal formulation; focus on extracellular synaptic PrP^Sc pool |
| Protease is immunogenic (foreign fungal protein) | Medium | Humanize or engineer a minimized catalytic domain; test single vs. repeated dosing; measure anti-drug antibodies |
Innovation Statement
This proposal is innovative on multiple levels:
- First cloning of a lichen prion-degrading protease — a 15-year gap in the literature addressed directly
- First demonstration of PrP β-sheet aggregates at peripheral nerve endings in chronic pain — a fundamentally new mechanism for CRPS
- First biological (non-small-molecule) therapy for chronic regional pain — a topical/injectable enzyme that degrades the pathological substrate itself, rather than modulating downstream signaling
- Cross-disciplinary convergence — lichenology × prion biology × pain neuroscience × protein engineering — a combination never before attempted
Significance and Impact
If successful, this work would:
- Identify the lichen serine protease — filling a 15-year gap and opening the door to engineering a thermostable, human-tolerated variant
- Validate a new pain mechanism — PrP β-sheet aggregation at injured peripheral nerve endings as a driver of chronic regional pain
- Provide a first-in-class topical therapeutic — a β-sheet-degrading enzyme applied at the time of surgery to prevent chronic pain, analogous to antibiotic prophylaxis for surgical site infection
- Offer a tool for other β-sheetopathies — the same enzyme could be tested in Alzheimer’s, Parkinson’s, and other protein aggregation diseases where peripheral pathology contributes to symptoms
Final Note
This proposal rests on a single, testable proposition:
If PrP β-sheet aggregates at peripheral nerve endings cause chronic pain, then specifically degrading those β-sheets with a targeted protease should resolve the pain.
The lichen serine protease — if it can finally be cloned — is the ideal tool for this experiment. Its existence in nature (evolved to degrade prions in the environment) provides the perfect starting point for an enzyme therapy that has no equivalent in the current pain pharmacopoeia.
