Related Experiment Video

Updated: Jul 30, 2026

Immunodetection of Outer Membrane Proteins by Flow Cytometry of Isolated Mitochondria
11:53

Immunodetection of Outer Membrane Proteins by Flow Cytometry of Isolated Mitochondria

Published on: September 18, 2014

Cloning and characterization of a 35-kDa mouse mitochondrial outer membrane protein MOM35 with high homology to Tom40

I L Rivera1, G C Shore, E Schleiff

  • 1Department of Biochemistry, McGill University, Montreal Quebec, Canada.

Journal of Bioenergetics and Biomembranes
|January 5, 2002
PubMed

Insights

Researchers identified MOM35, a mouse mitochondrial protein homologous to Tom40. This protein is imported into the outer mitochondrial membrane and interacts with preproteins, suggesting a role in mitochondrial protein import.

Area of Science:

  • Mitochondrial biogenesis and protein import
  • Molecular biology
  • Cellular and molecular physiology

Background:

  • Mitochondrial protein import is crucial for cellular function.
  • The TOM complex (Translocase of the Outer Membrane) is a key component of the mitochondrial protein import machinery.
  • Tom40 is a central pore-forming subunit of the TOM complex, but its mammalian homolog has not been fully characterized.

Purpose of the Study:

  • To identify and characterize a mammalian homolog of Tom40.
  • To investigate the function and localization of the identified protein within mitochondria.
  • To explore the interaction of this protein with other components of the mitochondrial import pathway.

Main Methods:

  • Cloning of a mouse cDNA library.
  • In vitro import assays into isolated mitochondria.
  • Proteolytic treatment (trypsin digestion) to assess membrane integration and structure.
  • In vitro interaction studies using purified proteins.

Main Results:

  • A 35-kDa protein, named MOM35, was cloned and found to share amino acid identity with yeast (yTom40) and Neurospora crassa (nTom40) Tom40 proteins.
  • Both long and short versions of MOM35 were successfully imported into mouse mitochondria in vitro.
  • MOM35 localized to the outer mitochondrial membrane and exhibited trypsin resistance similar to nTom40.
  • A highly conserved region within MOM35 specifically interacted in vitro with preproteins targeted by the Tom40-dependent pathway.

Conclusions:

  • MOM35 represents a functional homolog of Tom40 in mouse mitochondria.
  • The protein is integrated into the outer mitochondrial membrane.
  • MOM35 plays a role in the mitochondrial protein import pathway, potentially through interactions with preproteins via its conserved region.

More Related Videos

Two-Step Tag-Free Isolation of Mitochondria for Improved Protein Discovery and Quantification09:04

Two-Step Tag-Free Isolation of Mitochondria for Improved Protein Discovery and Quantification

Published on: June 2, 2023

An Improved Method to Isolate Mitochondrial Contact Sites07:55

An Improved Method to Isolate Mitochondrial Contact Sites

Published on: June 16, 2023

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...
Mitochondrial Precursor Proteins01:39

Mitochondrial Precursor Proteins

Mitochondrial precursors are partially unfolded or loosely folded polypeptide chains. Newly synthesized precursors are inhibited from spontaneously folding into their native conformation by the cytosolic chaperones, heat shock proteins 70 (Hsp70), and mitochondrial import stimulation factors (MSFs). Precursors bound to MSFs are guided to the TOM70-TOM37 receptors, while precursors bound to Hsp70  chaperones are targetted to TOM20-TOM22 receptor complexes.
Most of the 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...
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...