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Kathrin Lang

@klanglab.bsky.social

2.7K followers 969 following 40 posts

Prof for chemical biology at ETH Zurich Interested in: genetic code expansion - chembio tools - bioorthogonal chemistries - PTMs - Ub in all its shades - protein engineering

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Kathrin Lang @klanglab.bsky.social · 16/10/2025

Next, we asked if the system can be generalized. By varying the N-terminal residue, we created Z-XisoK tripeptides and evolved transporters for otherwise impermeable Z ncAAs, using GCE as readout for their delivery! Z-XisoKs even enable co-delivery and co-encoding of two distinct ncAAs! 8/9

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Kathrin Lang @klanglab.bsky.social · 16/10/2025

However, in nutrient-rich media (like 2-YT), uptake was less efficient – tryptic peptides present in such media competed for OppA binding. So we evolved OppA to prefer our substrates. Through FACS screening, we found OppA-iso and made the E. coli strain IsoK12, which thrives in complex media 💪 7/9

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Kathrin Lang @klanglab.bsky.social · 16/10/2025

This revealed how the transporter recognizes and delivers our substrates. What started as ‘unwanted cleavage’ turned into a transport system we could hijack. Opp imports G-XisoKs, peptidases remove G, accumulating high concentrations of XisoKs for efficient incorporation via aaRS/tRNA pairs. 5/9

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Kathrin Lang @klanglab.bsky.social · 16/10/2025

We discovered that E. coli actively imports G-XisoK peptides via the Opp ABC transporter that shuttles small peptides into cells in an ATP-driven manner. We mapped the uptake mechanism, identified the peptidases removing the N-terminal G and solved the OppA:G-SisoK structure with Michael Groll. 4/9

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Kathrin Lang @klanglab.bsky.social · 16/10/2025

Building on previous work from our lab on ubiquitin-protein conjugates, we aimed to incorporate G-XisoK ncAAs. Unexpectedly, the glycine was consistently cleaved off, leaving XisoK efficiently incorporated into proteins via GCE. A setback at first - we needed G-XisoK modified proteins. 2/9

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