Oxford · Pharmacology · Targeted Protein Degradation
Molecular Glue-like Degraders of TEM β-Lactamases
The first demonstration of targeted protein degradation in the bacterial periplasm. A small molecule hijacks DegP protease to eliminate the enzymes that confer antibiotic resistance.
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DC₅₀ (µM)
OXF232 lead compound
0
Fold improvement
vs tazobactam
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β-Lactamase variants
identified globally
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Microsomal t½ (min)
human + mouse
mechanism of action
How Periplasmic Degradation Works
Step through the mechanism. Use the controls to see how the degrader recruits DegP to eliminate β-lactamase in the periplasm.
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Step 1 of 4
TEM β-lactamase sits in the periplasm, hydrolysing β-lactam antibiotics and conferring resistance. DegP protease is present but not engaged.
in vitro data
Interactive Dose-Response
Drag the concentration slider to compare OXF232 and tazobactam. The degrader achieves DC₅₀ of 5.8 µM versus >100 µM for tazobactam.
OXF232 (degrader)
Tazobactam (inhibitor)
5.8
OXF232 DC₅₀ (µM)
>100
Tazobactam DC₅₀ (µM)
~17×
Potency improvement
Key finding
Unlinked tazobactam + FA dipeptide showed no enhanced degradation, confirming induced proximity is required. The components must be physically linked.
proteomics
C-Terminal Degron Code
Hover to explore amino acid enrichment at each C-terminal position of DegP substrates. Positions P9 and P10 show strong enrichment of hydrophobic residues.
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Proteins depleted
by WT DegP
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Proteins enriched
by S210A-DegP trap
Design rationale
Phenylalanine at P9 and Ala/Leu/Ile at P10 drive substrate recognition. Dipeptides FA, FI, FL were incorporated into degrader molecules as rational DegP recruiters.
chemistry
Two Linkage Strategies, One Winner
Two series of degraders were synthesised without linker groups, maintaining low molecular weight. The attachment chemistry proved decisive.
Triazole-linked (1-3)
OXF232 Tazobactam-triazole-FA
OXF233 Tazobactam-triazole-FI
OXF234 Tazobactam-triazole-FL
ROUTE: CuAAC click chemistry
Novel azide-tazobactam intermediate
Amide-linked (4-6)
FA (4), FI (5), FL (6)
Dipeptide coupled to tazobactam carboxylate
ROUTE: Microwave-assisted SPPS
Amide bond consumes carboxylate
Triazole series
Triazole linkage preserves the tazobactam carboxylate group, which is essential for β-lactamase binding. All three compounds (1-3) retain TEM-116 inhibitory activity and show potent degradation (DC₅₀ 5.8-6.9 µM). OXF232 (FA) was the best performer.
Degradation activity
Structure-activity
The carboxylate group is essential for β-lactamase binding. Amide linkage consumes it, destroying both inhibitory and degradation activity. Triazole linkage preserves it, enabling dual function.
the unexpected finding
A Weaker Inhibitor Makes a Better Degrader
Avibactam is a 6-fold more potent inhibitor of TEM-116 than tazobactam. Yet only tazobactam enhances DegP-mediated degradation. Inhibition and degradation are mechanistically distinct.
Inhibition IC₅₀
1.6 µM
Avibactam
BETTER INHIBITOR
Inhibition IC₅₀
9.5 µM
Tazobactam
WEAKER INHIBITOR
Degradation enhancement
Only tazobactam
Avibactam, sulbactam, clavulanic acid: no effect
SEC analysis revealed the mechanism: tazobactam alters TEM-116 conformational integrity, shifting it from a single monodisperse peak to multiple species. This destabilisation makes TEM-116 more susceptible to DegP recognition. Avibactam, despite stronger binding, does not induce this conformational change.
Why this matters
Tazobactam acts as a molecular glue by destabilising, not stabilising, its target. This is the opposite of classical PROTAC logic, where the target-binding ligand is chosen for tight, stable binding. It suggests a new design principle for bacterial degraders.
mechanistic proof
Induced Proximity, Not Independent Binding
Does OXF232 work because it brings TEM and DegP together, or could the two components work independently? Click each condition to see.
Condition
OXF232 (linked)
Condition
Tazo + FA (unlinked)
Condition
Tazobactam alone
Condition
FA dipeptide alone
OXF232 (linked)
Enhanced degradation of TEM-116 observed at 6h. DC₅₀ of 5.8 µM. The covalent linkage between tazobactam and FA dipeptide is required to simultaneously engage TEM-116 and recruit DegP through induced proximity.
TEM-116 degradation at 6h (100 µM compound)
Conclusion
Enhanced degradation requires the two pharmacophores to be physically linked. This is consistent with induced proximity between TEM-116 and DegP, rather than independent binary binding events. OXF232 functions as a true molecular glue-like degrader.
in vivo
The Concentration Crossover
Click each piperacillin concentration to see who wins. The answer changes with antibiotic pressure.
Low
0.1
mg/mL pip.
Medium
0.33
mg/mL pip.
High
1.0
mg/mL pip.
Tazobactam wins
At low β-lactam concentrations, the stoichiometric inhibitor is sufficient. Bacteria express lower levels of β-lactamase and DegP, so the catalytic advantage of degradation is not yet needed.
Mechanistic insight
Degraders become superior precisely when resistance is strongest. High antibiotic pressure drives β-lactamase overexpression and DegP stress response, creating ideal conditions for catalytic degradation.
pharmacokinetics
Drug-likeness Profile
Hover each axis on the radar to compare OXF232 against a typical PROTAC. The molecular glue-like design overcomes the fundamental size/PK penalty of bifunctional degraders.
OXF232 (this work)
Typical PROTAC
Property
OXF232 / OXF233
Typical PROTAC
Molecular weight
Low MW (glue-like)
>1,000 Da
Aqueous solubility
>175 µM (pH 7.4)
Often poor
LogD
<-1.4
Variable
Microsomal t½
>139 min (human + mouse)
Often rapid metabolism
Cytotoxicity (HEK293T)
Non-toxic <100 µM
Variable
Oral dosing potential
Compatible
Challenging
Clinical relevance
The molecular glue-like design avoids the pharmacokinetic challenges that have limited PROTAC development. High aqueous solubility, metabolic stability, and low mammalian toxicity make these compounds compatible with oral dosing, a critical advantage for antibiotic development.
summary
What This Establishes
1
First periplasmic targeted protein degradation: DegP degrades folded, active TEM β-lactamases in their native compartment
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Tazobactam acts as a molecular glue, inducing DegP-sensitive conformation in TEM-116
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Proteomics-guided design: C-terminal hydrophobic dipeptides as rational DegP recruiters
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~17× improvement in degradation potency with favourable PK for oral dosing
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Degraders outperform tazobactam when resistance is strongest, establishing a new mechanism of action against AMR
Ask Anything
Answers sourced exclusively from the primary materials. No external knowledge.
What is the DC₅₀ of OXF232?
Why tazobactam and not avibactam?
How were the dipeptides selected?
What are the PK properties?
Why do degraders win at high concentrations?
Source Materials
Original sources
Code-protected access to the underlying research artifacts.
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