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Related Concept Videos

Nuclear Export01:42

Nuclear Export

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The nucleus restricts several proteins within and allows others to pass. The restricted proteins possess a nuclear retention sequence or NRS, anchoring them to the nuclear lamins and preventing their transport to the cytosol. The non-restricted proteins, after their synthesis, are transported to their site of action, such as the cytosol or other organelles, with the help of nuclear export signals or NES.
NES are of three types- the canonical 10-residue long leucine-rich signal and other...
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Nuclear Protein Sorting01:34

Nuclear Protein Sorting

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Nuclear protein sorting is the selective trafficking of histones, polymerases, gene regulatory proteins into the nucleus and exporting RNAs and ribosomes to the cytosol. It is a tightly controlled process that regulates gene expression within a cell.
Proteins targeted to the nucleus carry nuclear localization signals or NLS recognized by import receptors in the cytosol. Similarly, proteins with nuclear export signals are recognized by export receptors. Import and export receptors are...
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Post-translational Translocation of Proteins to the RER01:27

Post-translational Translocation of Proteins to the RER

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A sizable fraction of proteins destined for ER are first synthesized in the cell cytosol and then transported across the ER membrane–a process called post-translational translocation. Similar to cotranslationally translocated proteins, these proteins also use the Sec translocon complex to enter the ER lumen.
Targeting proteins to the ER
Hsp40 and Hsp70 chaperone molecules bind the translated proteins in the cytosol to prevent their folding. The chaperone binding helps to keep the signal...
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Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

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Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
Sec61 channel partners for cotranslational translocation
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...
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Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
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Protein Translocation Machinery on the ER Membrane01:28

Protein Translocation Machinery on the ER Membrane

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The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
In eukaryotes, the translocon complex comprises a core heterotrimeric translocator channel called the Sec61 complex. This channel includes three transmembrane proteins, Sec61α, Sec61β, and Sec61γ, and is the largest subunit of the...
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Related Experiment Video

Updated: Sep 9, 2025

Purification of the Membrane Compartment for Endoplasmic Reticulum-associated Degradation of Exogenous Antigens in Cross-presentation
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Purification of the Membrane Compartment for Endoplasmic Reticulum-associated Degradation of Exogenous Antigens in Cross-presentation

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Nucleotide-dependent conformational changes direct peptide export by the transporter associated with antigen

James Lee1, Victor Manon2, Jue Chen3

  • 1Laboratory of Membrane Biophysics and Biology, the Rockefeller University, New York, NY 10065, USA.

Immunity
|August 30, 2025
PubMed
Summary

The transporter associated with antigen processing (TAP) moves peptides into the endoplasmic reticulum for immune responses. Cryo-EM structures reveal how TAP changes shape to transport and release peptides, preventing ER stress.

Keywords:
ABC transporterMHC-Iadaptive immunityantigen presentationnucleotide-binding domaintransporter associated with antigen processing

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Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies
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Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies
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Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies

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Area of Science:

  • Molecular Biology
  • Immunology
  • Structural Biology

Background:

  • The transporter associated with antigen processing (TAP) is crucial for adaptive immunity.
  • TAP facilitates the transport of antigenic peptides from the cytoplasm to the endoplasmic reticulum (ER).
  • This process is essential for loading peptides onto major histocompatibility complex class I (MHC-I) molecules.

Purpose of the Study:

  • To elucidate the structural mechanisms of peptide transport and release by the human TAP heterodimer.
  • To understand the functional states of TAP throughout its transport cycle.
  • To provide a structural basis for phenomena like vanadate trapping and trans-inhibition.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) was used to determine high-resolution structures.
  • Structures of the human TAP heterodimer were captured in multiple functional states.
  • Analysis focused on conformational changes related to ATP binding and hydrolysis.

Main Results:

  • Distinct inward-facing and outward-facing conformations of TAP were resolved.
  • ATP binding stabilizes the inward-facing state, exposing the peptide cavity to the cytosol.
  • Transition to the outward-facing state reconfigures the peptide-binding site for ER lumenal release.
  • ATP hydrolysis and nucleotide-binding domain separation drive the transport cycle and reset the transporter.

Conclusions:

  • A comprehensive structural framework for TAP-mediated peptide transport has been established.
  • The findings explain the mechanism of unilateral peptide transport and release.
  • The study illuminates the structural basis of trans-inhibition, a feedback mechanism preventing ER stress.