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Related Concept Videos

Mitochondrial Protein Sorting01:39

Mitochondrial Protein Sorting

Mitochondria are double-membrane organelles of the eukaryotes involved in cellular metabolism, signaling, ATP synthesis, and programmed cell death.  Each of these processes requires specific proteins and enzymes that must be correctly sorted to the right mitochondrial subcompartment for the proper functioning of the organelle.
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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,...
Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...
Protein Transport into the Inner Mitochondrial Membrane01:34

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 Import into the Peroxisomes01:27

Protein Import into the Peroxisomes

Cells contain membrane-bound organelles called peroxisomes that oxidize organic molecules by transferring hydrogen atoms to oxygen, producing hydrogen peroxide. Peroxisomes enzymatically convert the released hydrogen peroxide into water and oxygen.
Peroxisomal Protein Import:
Peroxisomes lack the genetic machinery required to code for their own proteins. Hence, most peroxisomal membrane, lumenal and transmembrane proteins are synthesized in the cytoplasm or ER and transported to the peroxisome...
Structure of Porins01:21

Structure of Porins

Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a  motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel precursors...

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Related Experiment Video

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Membrane Transport Processes Analyzed by a Highly Parallel Nanopore Chip System at Single Protein Resolution
11:55

Membrane Transport Processes Analyzed by a Highly Parallel Nanopore Chip System at Single Protein Resolution

Published on: August 16, 2016

Peroxisomal matrix protein import: the transient pore model.

Ralf Erdmann1, Wolfgang Schliebs

  • 1Institute for Physiological Chemistry, Faculty of Medicine, Ruhr-University Bochum, Germany. ralf.erdmann@rub.de

Nature Reviews. Molecular Cell Biology
|August 17, 2005
PubMed
Summary

Peroxisomes import folded proteins via a unique mechanism. This study proposes a three-step model involving pore formation, ubiquitylation, and receptor recycling for protein transport across the peroxisomal membrane.

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Organelle Biology

Background:

  • Peroxisomes import folded and oligomeric proteins, unlike other organelles.
  • The precise mechanism of protein transport across the peroxisomal membrane remains largely unknown.

Purpose of the Study:

  • To propose a mechanistic model for protein import into peroxisomes.
  • To elucidate the sequential steps involved in peroxisomal protein translocation.

Main Methods:

  • Conceptual modeling of the protein import pathway.
  • Analysis of peroxisomal protein translocation steps.

Main Results:

  • The proposed model divides peroxisomal protein import into three distinct stages.
  • These stages include translocation pore formation by import receptors, ubiquitylation of these receptors, and subsequent pore disassembly with receptor recycling.

Conclusions:

  • The mechanistic model provides a framework for understanding peroxisomal protein import.
  • This model highlights the roles of import receptors, ubiquitylation, and recycling in the process.