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M9M is a synthetic high-affinity nuclear transport peptide widely used as a selective inhibitor of Kapβ2/Transportin-1 (TNPO1)-mediated nuclear import. The peptide was developed by structure-based optimization of PY-type nuclear localization signal motifs and is commonly described in the literature as a superaffinity or “super-NLS” ligand for the Transportin pathway.
Unlike generic nuclear localization peptides, M9M is primarily used as a mechanistic research tool to competitively occupy the PY-NLS binding site of Kapβ2/Transportin. Because of its exceptionally tight interaction with the receptor, M9M has become a valuable reagent for dissecting pathway-specific nuclear import, differentiating Transportin-dependent cargoes from other import pathways, and evaluating the biological consequences of blocking Kapβ2 function.
Transportin/Kapβ2 recognizes PY-NLS-containing cargo proteins and mediates their nuclear import. In the original structure-guided design study, M9M was engineered as a Kapβ2-specific inhibitor with substantially higher affinity than natural PY-NLS ligands. Subsequent reviews and mechanistic studies have described M9M as a highly selective probe for the Transportin pathway rather than a general nuclear import inhibitor.
Applications in Biomedical Research
Nuclear Import and Transportin Pathway Studies
M9M is widely used to block TNPO1/Kapβ2-mediated import in cell-based and biochemical assays. Researchers use this peptide to validate whether a protein, peptide, or engineered construct depends on the Transportin pathway for nuclear entry.
- Kapβ2/Transportin inhibition assays
- Pathway-specific nuclear import studies
- Competitive binding studies with PY-NLS cargoes
- Nuclear transport mechanism research
RNA-Binding Protein and Neurodegeneration Research
The Transportin pathway is highly relevant to RNA-binding proteins such as FUS and hnRNP family members. Published studies have used M9M to interrogate Kapβ2-mediated chaperoning functions and to test how inhibition of Kapβ2 affects phase separation, stress granule behavior, and aggregation of disease-relevant proteins.
- FUS nuclear import studies
- Phase separation and condensate biology
- TDP-43 and aggregation-related research
- ALS/FTD mechanistic studies
Mitotic Assembly and Cell Biology
M9M has also been used as a tool to probe non-transport roles of Transportin in mitosis. In published Xenopus and cell studies, inhibition of Transportin with M9M helped reveal direct roles for Transportin in spindle assembly and nuclear pore-associated mitotic events.
- Mitotic spindle assembly studies
- Nuclear pore and kinetochore regulation
- Ran-dependent cell biology assays
- Cell cycle mechanism research
Wnt / β-Catenin Signaling Research
More recent studies have used M9M to inhibit TNPO1-dependent nuclear import of β-catenin, supporting its utility in probing Wnt pathway regulation and nuclear signaling mechanisms.
- β-catenin nuclear transport studies
- Wnt signaling pathway research
- Transport receptor target validation
- Cell signaling and transcriptional regulation assays
Key Features of M9M Peptide
- High-affinity Kapβ2/Transportin ligand
- Selective inhibitor of Transportin-dependent nuclear import
- Useful for competitive binding and mechanistic assays
- Widely cited tool in nuclear transport research
- Applicable to cell biology, neurobiology, and signaling studies
Why Researchers Use M9M
M9M is particularly useful when researchers need to distinguish Transportin-mediated import from importin α/β-dependent or other nuclear transport routes. Because it acts through competitive receptor engagement, it is often incorporated into mechanistic workflows where genetic knockout or knockdown approaches are impractical or where acute pathway inhibition is preferred.
The peptide is also useful in studies of Kapβ2 cargo recognition, cargo displacement, receptor occupancy, and nuclear transport regulation under stress, disease, or signaling conditions.
Research Use Statement
This product is intended for research use only. Not for human or therapeutic use.
Selected References
- Cansizoglu AE et al. Structure-based design of a pathway-specific nuclear import inhibitor.
- Chook YM and Suel KE. Nuclear import by Karyopherin-βs: recognition and inhibition.
- Bernis C et al. Transportin acts to regulate mitotic assembly events by target binding rather than Ran sequestration.
- Yoshizawa T et al. Nuclear import receptor inhibits phase separation of FUS.
- Hwang WY et al. Kap-β2/Transportin mediates β-catenin nuclear transport in Wnt signaling.
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