38YK

Cryo-EM structure of pSTAT1 bound to importin alpha 5 (2:1 assembly)

Summary for 38YK

• Entry DOI: 10.2210/pdb38yk/pdb
• Related: 11JG 11PH 38HT
• EMDB information: 75737 75922 78826 79237
• Descriptor: Importin subunit alpha-5, Signal transducer and activator of transcription 1-alpha/beta (2 entities in total)
• Functional Keywords: importin, transcription factor, transport protein, transcription
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 3
• Total formula weight: 235318.64

Authors

Kumar, P.,Vinkemeier, U.,Cingolani, G. (deposition date: 2026-09-23, release date: 2026-11-04)

Primary citation

Kumar, P.,Cavey, J.R.,Yang, R.,White, O.,Begitt, A.,He, L.,Suinn, S.S.,Bellis, N.F.,Lokareddy, R.K.,Vinkemeier, U.,Cingolani, G.
Cytokine-induced nuclear translocation of STAT1 via a non-transferable NLS.
Biorxiv, 2026

PubMed Abstract: The targeting function of nuclear localization signals (NLSs) is generally considered independent of a protein's native sequence or fold and is readily transferable to heterologous cargos. Contrary to this paradigm, rapid nuclear translocation of phosphorylated STAT1 (pSTAT1) following cytokine stimulation requires importin β, Ran-GTP, and the importin α5 isoform, which recognizes a non-transferable NLS. Here, we present cryo-EM structures of pSTAT1 bound to importin α5, revealing an asymmetric 2:1 complex that diverges from canonical NLS-mediated cargo recognition. Importin α5 occupies the DNA-binding groove of the pSTAT1 dimer, with a single STAT1 N-terminal domain positioning the C-terminal Armadillo repeats 9-10 (S1B domain) orthogonal to the DNA-binding interface. This interface is also targeted by the Ebola virus protein VP24, an antagonist of interferon signaling. We further show that Ran-GTP alone is insufficient to trigger nuclear release of pSTAT1, which additionally requires the exportin CAS. A cryo-EM reconstruction of the CAS-Ran-GTP-α5 complex, supported by in vitro competition assays, demonstrates that CAS and pSTAT1 are mutually exclusive ligands for importin α5. Together, these findings define the molecular choreography of cytokine-induced STAT1 nuclear translocation and release, establishing a general paradigm for STAT family signaling.

PubMed: 42856475
DOI: 10.64898/2026.09.28.754937

Experimental method

ELECTRON MICROSCOPY (3.6 Å)