Enzyme Engineering & Biocatalysis
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Protease Specificity Engineering
Protease Engineering
How much proteome-wide cleavage specificity survives transfer from E. coli to HEK293 lysate across eight OmpT variants with 0–2 versus 5–7 contact mutations?
THE QUESTION
Which mutation set narrows cleavage specificity to a named target sequence with off-target cleavage below [threshold], measured proteome-wide rather than on a single reporter? Verifier: expressed panel with MS-based cleavage-site profiling. [baseline: to verify]
WORK ORDER
Portability of engineered OmpT protease specificity across bacterial and mammalian proteomes
BACKGROUND
What this Apodex Lab is
When an engineered protease enters a living cell, its precision determines whether it cuts only a desired target or destroys essential host proteins. Therapeutic and diagnostic enzymes require strict selectivity, yet residual off-target cleavage can lead to unintended toxicity. Current protein engineering typically measures specificity against isolated artificial reporters or small panels of decoy sequences. Inside a real biological environment, however, native proteins vary in abundance across six or more orders of magnitude, differ in physical accessibility, and compete simultaneously for the catalytic site. A protease that appears selective against a single synthetic substrate can produce widespread off-target cuts when exposed to a whole proteome.
Directed-evolution campaigns report variants as specific when they cleave a chosen reporter while sparing a handful of counter-substrates in microbial hosts such as Escherichia coli. This assay format strips out the cellular context entirely. It leaves unresolved whether off-target cleavage is primarily encoded in the recognition sequence or imposed by the background proteome itself through substrate abundance, steric hindrance, and molecular competition. Until recently, measuring the full distribution of cleavable sites across thousands of variants was technically impractical. While modern DNA-recording readouts can quantify cleavage landscapes for tens of thousands of variants in living cells, they do so within a single host where the proteome context remains fixed. Nobody has measured whether a protease's proteome-wide cleavage-site ranking survives when transferred from a microbial selection host to a mammalian background.
The Protease Engineering Apodex Lab establishes this transferability by profiling an eight-member panel of OmpT protease variants across both Escherichia coli and HEK293 cell lysates. Using subtiligase-based N-terminomics and high-resolution mass spectrometry, the measurement compares four lightly engineered variants carrying 0–2 contact substitutions against four heavily engineered variants carrying 5–7 substitutions. It delivers replicate-calibrated transfer coefficients that quantify how consistently cleavage-site rankings hold between the two proteomes. If the mean transfer coefficient falls at or below 0.70, selection-host specificity assays cannot support off-target claims, mandating cleavage profiling in the intended deployment background before locking therapeutic candidates. If group means reach 0.80 or above, selection-host rankings are validated for candidate triage, confirming that sequence-encoded preferences dominate proteome context.
WHY NOW
Why the field is spending on an assumption
Protease specificity is routinely evolved against single reporter substrates, treating off-target cleavage as downstream quality control. While DNA-recording readouts can now screen 29,716 variants in a single campaign, they profile sequences within a single host. Subtiligase N-terminomics allows whole-proteome cleavage-site mapping by mass spectrometry, yet these methods have not been paired. The field cannot determine how much residual off-target cleavage reflects intrinsic sequence preference versus host proteome context, such as substrate abundance spanning six orders of magnitude and cleavage-site accessibility. Consequently, specificity rankings obtained in a selection host cannot be guaranteed to hold in target mammalian proteomes.
WHAT WE’D BUY
What we would ask a laboratory to run
We are not buying the answer. We are buying a measurement with an interval — and the bars it will be compared against.
Eight OmpT protease variants on one scaffold, comprising four with 0–2 substituted contact positions and four with 5–7, are expressed, purified from Escherichia coli, and matched by activity on a fluorogenic substrate. Each variant is applied to cell-free Escherichia coli and HEK293 lysates, with cleavage sites mapped by subtiligase N-terminomics and mass spectrometry across 42 runs. The measurement returns replicate-calibrated transfer coefficients that quantify how cleavage-site rankings correlate across backgrounds. Deliverables include mean transfer coefficients for both mutation-load groups with 95% bootstrap confidence intervals of half-width about 0.07, eight individual variant coefficients with interval half-widths no greater than 0.12, and the group difference to about 0.13.
SCOPE & LIMITS
Because cell-free lysates lack intact compartmentalisation and native complex assembly, the measured context dependence reflects substrate abundance, accessibility, and competition rather than compartmental exclusion inside intact cells.
WHO EXECUTES
The kind of lab that can run this
A protein-engineering CRO with E. coli and mammalian expression capability, a DNA-recording/deep-sequencing workstream, and an in-house LC-MS/MS proteomics core able to run N-terminomics (TAILS or subtiligase-based) cleavage-site profiling on whole proteome lysates.
EXECUTOR KIND
wet-lab
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