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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.
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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:
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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.
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Related Experiment Video

Updated: Jun 12, 2026

Unveiling Xenobiotic Transport and Effects in Isolated Mitochondria: Insights from Respirometric and Enzymatic Assays

Unveiling Xenobiotic Transport and Effects in Isolated Mitochondria: Insights from Respirometric and Enzymatic Assays

Published on: March 7, 2025

Mitochondrial metabolite transport.

Ferdinando Palmieri¹, Ciro Leonardo Pierri

¹Department of Pharmaco-Biology, Laboratory of Biochemistry and Molecular Biology, University of Bari, 70125 Bari, Italy. fpalm@farmbiol.uniba.it

Essays in Biochemistry

|June 11, 2010

Summary

Mitochondrial carriers (MCs) transport essential molecules across the inner mitochondrial membrane. Recent studies reveal conserved structural features and a common transport mechanism for these vital proteins.

Area of Science:

Biochemistry
Molecular Biology
Cell Biology

Background:

Mitochondrial carriers (MCs) are nuclear-coded secondary transporters crucial for metabolite, nucleotide, and coenzyme flux across the inner mitochondrial membrane.
These proteins are vital in all eukaryotes, involved in numerous metabolic pathways and cellular functions, with genetic alterations linked to diseases.
MCs possess conserved sequence features, enabling their identification in biological databases.

Purpose of the Study:

To elucidate the transport mechanism of mitochondrial carriers (MCs).
To understand the structural basis for substrate translocation in MCs.

Main Methods:

Functional characterization of 22 MC subfamilies through transport assays.
Heterologous gene expression, protein purification, and reconstitution into liposomes.

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Analysis of sequence conservation and homology modeling.

Main Results:

Evidence suggests a common transport mechanism for all MCs, despite variations in substrate and transport modes.
New insights point to a substrate-binding site within the carrier cavity.
Conserved proline and glycine residues in transmembrane helices and the presence of cytosolic and matrix gates are identified as key structural elements.

Conclusions:

The identified structural properties, including gates and conserved residues, are critical for the conformational changes enabling substrate translocation.
Understanding MC structure and mechanism provides insights into mitochondrial function and disease pathogenesis.