Mitochondrial Protein Import Mechanisms and Dynamics

Mitochondria are essential organelles whose functions span energy conversion, metabolism and signalling. Most of their 1,000–1,500 proteins are synthesised in the cytosol and rely on an intricate import system to reach specific subcompartments. Entry is mediated by the translocase of the outer membrane (TOM) complex, which recognises targeting signals such as presequences or internal motifs. Following outer‐membrane passage, precursors engage distinct pathways: the TIM23 complex and its associated motor (PAM) for matrix and inner‐membrane preproteins, and the TIM22 complex for carrier proteins. These translocases harness membrane potential and ATP‐powered chaperone cycles to drive directional translocation. Import is further integrated with mitochondrial dynamics via contact sites that coordinate membrane fusion and fission, linking proteome maintenance to organelle morphology. Quality‐control modules at the entry gate and within the matrix monitor stalled or misfolded precursors, directing them to ubiquitination, deubiquitination or proteolytic removal. Recent advances have elucidated the structural plasticity of import assemblies, their regulation by post‐translational modifications and their responsiveness to cellular stress, highlighting a dynamic interplay between protein trafficking, organelle biogenesis and metabolic adaptation.

Research from Nature Portfolio

High‐resolution complexome profiling in yeast has resolved over 5,200 assembly peaks across the mitochondrial proteome, revealing distinct modules for respiratory complexes, import receptors and quality‐control factors. This resource uncovers pathways for preprotein ubiquitylation, deubiquitylation and degradation at the entry gate, and identifies a constitutive removal route for mislocalised precursors. In human cells, delayed mitochondrial import under stress triggers upregulation of chaperones and induces an immunoproteasome subunit, PSMB9, via EEF1A2. This adaptation modulates proteasome composition and activity to preserve cellular proteostasis, offering new therapeutic angles for neurodegenerative diseases.

Mitochondrial Protein Import Mechanisms and Dynamics publication trend

The graph below shows the total number of articles in mitochondrial protein import mechanisms and dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Presequence: An N‐terminal targeting signal that directs a precursor protein to the mitochondrial matrix or inner membrane.

TOM complex: The translocase of the outer mitochondrial membrane that recognises and imports cytosolic preproteins.

TIM23 complex: The translocase of the inner mitochondrial membrane responsible for presequence‐containing proteins, often associated with a motor in the matrix.

Complexome profiling: A quantitative method for mapping the composition and interactions of protein assemblies within organelles.

Proteostasis: The maintenance of cellular protein homeostasis through synthesis, folding, trafficking and degradation mechanisms.

References

1. Mitochondrial complexome reveals quality-control pathways of protein import. Nature (2023).
2. Immunoproteasome-specific subunit PSMB9 induction is required to regulate cellular proteostasis upon mitochondrial dysfunction. Nature Communications (2023).
3. Mitochondrial Machineries for Protein Import and Assembly. Annual Review of Biochemistry (2017).
4. MitoFates: Improved Prediction of Mitochondrial Targeting Sequences and Their Cleavage Sites*[S]. Molecular & Cellular Proteomics (2015).
5. Hsp70 at the membrane: driving protein translocation. BMC Biology (2018).