Related Experiment Video

Updated: Jun 23, 2026

Experimental Approaches to Study Mitochondrial Localization and Function of a Nuclear Cell Cycle Kinase, Cdk1
13:15

Experimental Approaches to Study Mitochondrial Localization and Function of a Nuclear Cell Cycle Kinase, Cdk1

Published on: February 25, 2016

Mitochondrial targeting of cytochrome P450 proteins containing NH2-terminal chimeric signals involves an unusual

Hindupur K Anandatheerthavarada1, Naresh Babu V Sepuri1, Narayan G Avadhani1

  • 1From the Department of Animal Biology and the Mari Lowe Center for Comparative Oncology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104.

The Journal of Biological Chemistry
|April 30, 2009
PubMed

Insights

This study reveals how chimeric signals guide cytochrome P450 proteins to mitochondria. Chaperone interactions with mitochondrial outer membrane translocases (TOMs) dictate import pathways, showing evolved targeting mechanisms.

Area of Science:

  • Mitochondrial biology
  • Protein import
  • Cellular signaling

Background:

  • Xenobiotic-inducible cytochrome P450 (CYP) proteins are targeted to both endoplasmic reticulum and mitochondria.
  • Understanding the precise mechanisms of mitochondrial protein import is crucial for cellular function.

Purpose of the Study:

  • To investigate the mechanism of delivery for chimeric signal-containing CYP proteins to mitochondrial outer membrane translocases (TOMs).
  • To elucidate the role of specific TOM components and cytosolic chaperones in this import process.

Main Methods:

  • Utilized chimeric CYP proteins with varying signal sequences.
  • Assessed protein translocation through TOM complexes.
  • Investigated interactions with cytosolic chaperones Hsp70 and Hsp90.
  • Examined the role of specific TOM40 domains in protein import.

Main Results:

  • Different chimeric CYP signals exhibited distinct requirements for peripheral TOM proteins (TOM70, TOM20, TOM22).
  • Interaction with Hsp70 alone was sufficient for recognition by peripheral TOMs.
  • Sequential interaction with Hsp70 and Hsp90 facilitated bypass of peripheral TOMs.
  • Hsp90-mediated import required specific N-terminal domains of TOM40.

Conclusions:

  • Chimeric mitochondrial targeting signals are highly evolved and dynamic.
  • The interplay between cytosolic chaperones and TOM complex components governs the import pathway of chimeric signal-containing CYPs.
  • These findings offer new insights into the complexity of mitochondrial protein targeting.

More Related Videos

Reconstitution of Msp1 Extraction Activity with Fully Purified Components05:52

Reconstitution of Msp1 Extraction Activity with Fully Purified Components

Published on: August 10, 2021

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

Related Concept Videos

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,...
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...
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...
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...
Energy to Drive Translocation01:37

Energy to Drive Translocation

Mitochondrial protein import is powered by two distinct energy sources: ATP hydrolysis and electrochemical potential across the inner membrane. Newly synthesized precursors are bound by cytosolic chaperones of the Hsp70 family, which guide them to the import receptors on the mitochondrial surface. Utilizing the energy of ATP hydrolysis, Hsp70 chaperones transfer these precursors to the TOM receptors on the mitochondrial outer membrane.
Generally, polypeptides are unfolded by two distinct...
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...