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Post-translational Translocation of Proteins to the RER

Post-translational Translocation of Proteins to the RER

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...

Cotranslational Protein Translocation

Cotranslational Protein Translocation

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...

Overview of Protein Sorting and Transport

Overview of Protein Sorting and Transport

Eukaryotic cells have different membrane-bound organelles with distinct protein requirements. The process by which proteins are targeted to a specific organelle is called protein sorting.
Protein sorting can be of two types: signal-based sorting and vesicle-based trafficking. In signal-based sorting, specific amino acid sequences called sorting signals target proteins to the proper location inside the cell either via gated transport or by protein translocation. In gated transport, folded...

Protein Transport to the Thylakoids

Protein Transport to the Thylakoids

Thylakoids are membrane-bound sac-like structures within the chloroplast that serve as sites for photosynthesis. Thylakoid lumen contains many electron transport proteins and is enclosed by a thylakoid membrane rich in the light-harvesting complex. Proteins targeted to the thylakoids are transported as precursors and are sorted by the general TOC/TIC import pathway. Once the precursor reaches the stroma, stromal processing peptidases remove their transit signal and expose thylakoid signal...

Protein Transport into the Inner Mitochondrial Membrane

Protein Transport into the Inner Mitochondrial Membrane

Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation.
Transport of mitochondrial precursors across the TIM23 channel is driven by...

Protein Translocation Machinery on the ER Membrane

Protein Translocation Machinery on the ER Membrane

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 translocon complex.

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Updated: May 9, 2026

Development of a Microfluidics-Based Approach for Investigating Microtubule Polymer Mechanics

Development of a Microfluidics-Based Approach for Investigating Microtubule Polymer Mechanics

Published on: May 30, 2025

Polymer translocation through a gradient channel.

Shuang Zhang¹, Chao Wang, Li-Zhen Sun

¹Department of Physics, Zhejiang University, Hangzhou 310027, China.

The Journal of Chemical Physics

|August 2, 2013

Summary

This summary is machine-generated.

This study investigates polymer translocation through channels with energy gradients. We found a minimum translocation time dependent on the energy gradient, with distinct scaling behaviors for short and long polymers.

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Single-Molecule Diffusion and Assembly on Polymer-Crowded Lipid Membranes

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Published on: July 19, 2022

Area of Science:

Polymer physics
Soft matter physics
Statistical mechanics

Background:

Understanding polymer translocation through confined geometries is crucial for nanotechnology and biophysics.
The influence of channel-polymer interactions on translocation dynamics is a key research area.

Purpose of the Study:

To investigate the impact of a linear energy gradient on polymer translocation dynamics.
To determine the mean first passage time (τ) for polymers of varying lengths (N) through a channel of length (L).
To analyze the scaling relationships of translocation time under different driving forces (f) and energy gradients (k).

Main Methods:

Utilizing the Fokker-Planck equation to model polymer translocation.
Calculating the mean first passage time (τ) for two cases: N > L and N < L.
Assuming a constant diffusion rate (D) for the polymer.

Main Results:

A minimum mean first passage time (τ) is observed at a critical energy gradient (k = k(c)) for both N > L and N < L cases.
The critical gradient k(c) depends on the initial potential energy (E0) and the driving force (f).
For long polymers and large driving forces, τ scales linearly with polymer length (τ ∼ N).

Conclusions:

The energy gradient significantly influences polymer translocation time, with an optimal gradient for fastest translocation.
Scaling relationships are dependent on both polymer length and the presence/strength of an energy gradient.
This work provides insights into controlling polymer dynamics in nanopores and channels.