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Updated: Jul 14, 2026
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Nitrogen Cavitation and Differential Centrifugation Allows for Monitoring the Distribution of Peripheral Membrane Proteins in Cultured Cells
Published on: August 18, 2017
Early sorting of inner nuclear membrane proteins is conserved
Sharon C Braunagel1, Shawn T Williamson, Qi Ding
1Department of Biology, Texas Agricultural Experiment Station, Texas A&M University, College Station, TX 77843, USA.
Summary
Insect cells
Area of Science:
- Cell Biology
- Molecular Biology
- Protein Trafficking
Background:
- Importin-alpha-16 in Spodoptera frugiperda (Sf9) cells is a translocon-associated protein crucial for sorting baculovirus integral membrane proteins to the inner nuclear membrane (INM).
- Investigating conserved sorting mechanisms between insect and mammalian cells is vital for understanding protein transport.
- The inner nuclear membrane (INM) plays a critical role in nuclear structure and gene regulation.
Purpose of the Study:
- To determine if similar protein complexes involved in INM protein sorting, as observed in insect cells, are formed with mammalian INM proteins.
- To identify mammalian importin-alpha isoforms that may recognize INM-directed proteins.
- To explore the conservation of the early sorting pathway for INM proteins.
Main Methods:
- Cross-linking experiments were performed using Sf9 importin-alpha-16 with human inner nuclear membrane proteins lamin B receptor (LBR) and nurim.
- Analysis of protein complex formation during cotranslational membrane integration and after release from the translocon.
- Testing of human importin-alpha isoforms for cross-linking with a viral-derived INM sorting motif sequence.
Main Results:
- Both human LBR and nurim cross-linked with Sf9 importin-alpha-16 during membrane integration and remained associated after release from the translocon.
- A specific 16-kDa isoform of importin-alpha, encoded by KPNA4 (KPNA-4-16), was found to cross-link with the viral INM sorting motif.
- KPNA-4-16 was detected in microsomal membranes from both recombinant virus-infected cells and HeLa cells.
Conclusions:
- The early sorting pathway for INM-directed proteins mediated by importin-alpha-16 shows high conservation between insect and mammalian systems.
- Mammalian KPNA-4-16 is identified as a potential partner protein involved in the sorting of integral membrane proteins to the inner nuclear membrane.
- These findings suggest conserved molecular mechanisms for targeting proteins to the INM across different species.
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