Abstract
N-terminal signal peptides (SPs) are traditionally considered as drivers of co-translational translocation of newly synthesised proteins into the endoplasmic reticulum (ER). However, growing evidences suggest that proteins with SPs can also undergo post-translational insertion into the ER membrane after synthesis is complete. Recently, an intermediate third mechanism has been uncovered where proteins with marginally hydrophobic or suboptimal SPs are translocated following an initial delay after translation initiation. Here, we show that this “delayed translocation” allows a temporary exposure of the nascent chain to the cytosolic environment, enabling exoplasmic domain modifications by cytosolic enzymes. We report that programmed death ligand-1 (PD-L1) follows this pathway, featuring a suboptimal SP that exposes its extracellular domain to the cytosol, enabling AMPK-dependent regulation of PD-L1 function. Importantly, optimising the SP of PD-L1 eliminates the cytosolic exposure, disrupting PD-L1’s trafficking and maturation, highlighting the physiological importance of the delayed translocation mechanism.
Data availability
All data are available in the article and supplementary information. The source data for all data presented in the figures are provided with this paper as a Source Data file. Original uncropped gels are provided in the supplementary information file. Material is available upon request. The presented research complies with all relevant ethical regulations. Source data are provided with this paper.
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Acknowledgements
We acknowledge Bruno Goud (Institut Curie, Paris), Maria Antonietta De Matteis (Tigem, Pozzuoli), Stefano Bonatti and Tommaso Russo (DMMBM, UNINA) for sharing reagents, scientific support and helpful discussions. We acknowledge Alice Ting for the plasmid V5-TurboID-NES_pCDNA3 (Addgene plasmid #107169). We thank the Cell and Tissue Imaging (PICT-IBiSA, Institut Curie), a member of the French National Research Infrastructure France-BioImaging (ANR10-INBS-04). This work in the M.D.A. lab has been funded by the Italian Minister for Research and University (PRIN B53D2300249006), the Italian Minister for Research and University (PRIN 20177XJCHX) to M.R., and the STAR-Junior Principal Investigator Grants 2018 to S.R. The work in F.P. lab has been supported by the Fondation pour la Recherche Médicale (EQU201903007925), by the Agence Nationale de la Recherche (ANR-19-CE13- 0006-03; ANR-20-CE14-0017-02; ANR-19-CE13-0002-03; ANR-11-LABX-0038), and has also received support under the program «Investissements d’Avenir» launched by the French Government and implemented by ANR with the references CelTisPhyBio (11-LBX-0038), ANR-10-IDEX-0001-02 PSL. The work of M.C.S. has been supported by grants ANR-11-LABX-0038 and ANR-10-IDEX-0001-02.
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Conceptualisation: M. D. A., F. P. and M. C. S. Experiments design: G. S., M. C. S., F. V., S. R., L. M., M. R., F. P., M. D. A. Investigation: G. S., M. C. S., F. V., R. B., P. P., M. G. C., S. R. and L. M. Funding acquisition: M. D. A., F. P. and M. R. Writing – original draft: M. D. A., F. P. and M. C. S. Writing – review & editing: All the authors read, revised and edited the manuscript.
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Cannata Serio, M., Vitale, F., Scerra, G. et al. A delayed translocation into the endoplasmic reticulum controls the post-translational modifications of PD-L1. Nat Commun (2026). https://doi.org/10.1038/s41467-026-71760-x
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DOI: https://doi.org/10.1038/s41467-026-71760-x
