TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)

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TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)

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TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)</th>
</tr>
<tr>
<td class="label">Component</td>
<td>Function</td>
</tr>
<tr>
<td class="label">TIM23</td>
<td>Channel-forming subunit, lateral gate</td>
</tr>
<tr>
<td class="label">Tim17</td>
<td>IMS domain, substrate access</td>
</tr>
<tr>
<td class="label">Tim21</td>
<td>Assembly, interaction with OXPHOS</td>
</tr>
<tr>
<td class="label">Tim50</td>
<td>Transfer to Tim23 from TOM</td>
</tr>
<tr>
<td class="label">Tim44 (matrix)</td>
<td>Motor recruitment</td>
</tr>
</table>

Overview

TIM23 is a core component of the mitochondrial protein import machinery that resides in the inner mitochondrial membrane. As part of the TIM23 complex (translocase of the inner mitochondrial membrane 23), TIM23 forms a channel through which precursor proteins are imported from the cytosol into the mitochondrial matrix or inserted into the inner membrane[@tim23_structure]. This essential translocase mediates the import of over 1,000 nuclear-encoded proteins that are synthesized in the cytosol but function within mitochondria, including critical components of the electron transport chain, ATP synthase, and mitochondrial ribosomes.

...

TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)</th>
</tr>
<tr>
<td class="label">Component</td>
<td>Function</td>
</tr>
<tr>
<td class="label">TIM23</td>
<td>Channel-forming subunit, lateral gate</td>
</tr>
<tr>
<td class="label">Tim17</td>
<td>IMS domain, substrate access</td>
</tr>
<tr>
<td class="label">Tim21</td>
<td>Assembly, interaction with OXPHOS</td>
</tr>
<tr>
<td class="label">Tim50</td>
<td>Transfer to Tim23 from TOM</td>
</tr>
<tr>
<td class="label">Tim44 (matrix)</td>
<td>Motor recruitment</td>
</tr>
</table>

Overview

TIM23 is a core component of the mitochondrial protein import machinery that resides in the inner mitochondrial membrane. As part of the TIM23 complex (translocase of the inner mitochondrial membrane 23), TIM23 forms a channel through which precursor proteins are imported from the cytosol into the mitochondrial matrix or inserted into the inner membrane[@tim23_structure]. This essential translocase mediates the import of over 1,000 nuclear-encoded proteins that are synthesized in the cytosol but function within mitochondria, including critical components of the electron transport chain, ATP synthase, and mitochondrial ribosomes.

Given the central role of mitochondria in neuronal function—particularly in high-energy demanding dopaminergic neurons and other neuronal subtypes—TIM23-mediated protein import is fundamental to neuronal survival. Dysregulation of mitochondrial protein import has emerged as a significant contributor to neurodegenerative disease pathogenesis, particularly in Parkinson's disease where complex I deficiency is a hallmark feature and in Alzheimer's disease where mitochondrial dysfunction is an early event[@pd_mitochondria][@ad_mitochondria].

Protein Structure and Biochemistry

Domain Architecture

TIM23 is a ~16 kDa integral membrane protein with distinctive structural features:

Transmembrane domain (residues ~50-70): Single α-helical transmembrane segment that anchors TIM23 in the inner mitochondrial membrane
N-terminal region (residues 1-50): Faces the intermembrane space (IMS), contains substrate-binding sites
C-terminal region (residues 70-150): Faces the matrix, contains interaction domains
Lateral gate: Allows substrate release into the lipid phase of the membrane

The protein adopts a overall "L"-shaped architecture with:

One transmembrane helix (anchor)
Two soluble domains (IMS and matrix-facing)
Flexible linker connecting them

TIM23 shares structural homology with other Tim17/Tim22/Tim23 family members:

Tim17: Most similar, also small IMS-facing subunit
Tim22: Central transport channel

The TIM23 Complex

TIM23 operates as part of a larger complex:

The core TIM23 complex contains TIM23 and Tim17 in a 1:1 ratio, forming the minimal translocase channel.

Structural Mechanism

The TIM23 channel operates through conformational changes[@tim23_mechanism]:

Closed state: Resting, sealed channel

Substrate binding: N-terminal presequence recognized

Channel opening: Lateral gate opens

Insertion/release: Substrate enters membrane or passes to matrix

Normal Physiological Functions

Mitochondrial Protein Import

The primary function of TIM23 is importing precursor proteins synthesized in the cytosol[@mitochondrial_import]:

Import Pathway:

Cytosolic targeting: precursor proteins contain N-terminal presequence (amphipathic helix)

TOM complex recognition: Outer membrane translocase receives substrate

TOM-TIM transfer: Passed to TIM23 complex

Import into matrix: TIM23 channel, with mtHsp70 motor

Inner membrane insertion: Lateral gating for membrane proteins

Substrate Types:

Matrix proteins: Fully imported, presequence cleaved
Inner membrane proteins: Insertion via lateral gate
Intermembrane space proteins: Oxidative folding

Energy Coupling

TIM23 import requires energy:

ATP: mtHsp70 in matrix provides driving force
ΔΨm: Inner membrane potential aids import of positively charged presequences

The membrane potential (ΔΨm) is essential—depolarization impairs import.

Coordination with TOM

TIM23 functions in concert with the TOM complex (translocase of outer membrane)[@tom_complex]:

TOM: Recognizes substrates, translocates across outer membrane
TOM-TIM relay: Tim50 bridges complexes
Synchronized operation: Coupled import

Import of Critical Proteins

TIM23 imports numerous essential proteins:

Electron Transport Chain subunits:

Complex I subunits (NADH dehydrogenase)
Complex III (cytochrome bc1)
Complex IV (cytochrome c oxidase)
ATP synthase subunits

Other essential proteins:

Mitochondrial DNA-encoded proteins require import
tRNA synthetases
Metabolic enzymes

Regulation of Import

TIM23 activity is regulated[@tim23_assembly]:

Assembly state: Dynamic complex formation
ΔΨm: Membrane potential affects function
Oxidative stress: Can impair function

Role in Parkinson's Disease

Mitochondrial Dysfunction in PD

Parkinson's disease involves prominent mitochondrial dysfunction[@complex_i]:

Complex I Deficiency:

Reduced complex I activity in substantia nigra
Affects dopaminergic neuron survival
Requires proper import of complex I subunits

TIM23 Contributions:

Imports NADH dehydrogenase subunits
Requires ΔΨm maintained
Disrupted import contributes to deficiency

Pink1/Parkin Pathway

The PINK1/Parkin mitophagy pathway intersects with TIM23 function[@pink1_parkin]:

Damaged mitochondria lose ΔΨm
Impaired TIM23 import under stress
PINK1 accumulation tags for mitophagy

Pathological Cascade:

Mitochondrial stress → ΔΨm loss

TIM23 import defects

PINK1 accumulation on surface

Parkin recruitment, mitophagy

Dopaminergic Neuron Vulnerability

Dopaminergic neurons in the substantia nigra pars compacta show particular vulnerability:

High Energy Demands:

Pacemaker firing requires ATP
Mitochondrial function essential
TIM23 import critical

Susceptibility Factors:

Dopamine metabolism creates oxidative stress
High calcium influx
Relies on mitochondrial import

Therapeutic Implications

Targeting mitochondrial protein import in PD:

Stabilizing Import:

Preserve ΔΨm
Enhance TIM23 function
Protect against stress

Role in Alzheimer's Disease

Mitochondrial Dysfunction in AD

Alzheimer's disease involves significant mitochondrial dysfunction[@ad_mitochondria]:

Early Changes:

Reduced cerebral glucose metabolism
Altered mitochondrial dynamics
Impaired protein import

Contributing Factors:

Aβ toxicity affects mitochondria
Tau pathology disrupts function
Oxidative stress damages import

Amyloid-β Toxicity

Aβ localizes to mitochondria and affects function[@amyloid_mitochondria]:

Aβ accumulation in mitochondria
Impairs protein import
Reduces complex IV activity
Disrupts ΔΨm

Tau Pathology

Tau pathology intersects with mitochondrial function:

Mitochondrial trafficking disrupted
Distribution altered
Local function affected

Energy Failure

The brain relies heavily on oxidative phosphorylation[@energy_brain]:

Neurons require high ATP
Mitochondrial import essential
Failure contributes to dysfunction

Role in ALS

Amyotrophic lateral sclerosis involves mitochondrial dysfunction[@als_mitochondria]:

Motor Neuron Vulnerability:

High energy demands
Long axons requiring mitochondria
Calcium handling importance

TIM23 Contributions:

Impaired import in disease
Respiratory chain defects

Role in Other Neurodegenerative Conditions

Huntington's Disease

Mitochondrial dysfunction
Energy impairment
Import may be affected

Frontotemporal Dementia

Mitochondrial changes
May affect import

Aging

Mitochondrial function declines with age[@tim23_aging]:

Import efficiency decreases
ΔΨm reduced
Contributes to age-related decline

Mitochondrial Quality Control

Import Quality Control

Proper import ensures protein quality:

Folding assistance: Matrix chaperones
Mistargeting: Degradation pathways
Failed import: Turnover

Turnover and Replacement

TIM23 and imported proteins are turned over:

Protein quality control
Assembly checks
Replacement of damaged components

Therapeutic Strategies

Small Molecules

Mitochondrial protectants:

Maintain ΔΨm
Enhance import
Antioxidants

Targeting TIM23:

Stabilize function
Enhance assembly

Gene Therapy

Overexpression of TIM components
Enhancement of import machinery

Exercise and Lifestyle

Exercise enhances mitochondrial function:

Increased mitochondrial biogenesis
Improved import
Protective effects

Biomarkers

TIM23 activity or assembly may serve as biomarker:

Mitochondrial import efficiency
Complex assembly state

Research Methods

Biochemical Studies

Import assays in vitro
Blue-native PAGE
Pull-down experiments

Imaging

MitoTimer reporters
GFP-based import assays
Super-resolution microscopy

Genetic Studies

siRNA knockdown
CRISPR editing
Patient mutations

Evolutionary Conservation

TIM23 is evolutionarily conserved[@tim23_evolution]:

Present in all eukaryotes
Derived from bacterial ancestor
Essential for mitochondrial function

Summary

TIM23 is an essential component of the mitochondrial protein import machinery, forming the channel through which nuclear-encoded proteins are imported into the mitochondrial inner membrane or matrix. This function is critical for maintaining the electron transport chain, ATP production, and overall mitochondrial function. In neurodegenerative diseases including Parkinson's and Alzheimer's, mitochondrial dysfunction is a hallmark, and impaired protein import through TIM23 contributes to this pathology. The particular vulnerability of dopaminergic neurons in PD—due to their high energy demands—makes proper TIM23 function especially important. Therapeutic approaches targeting mitochondrial protein import, including stabilizing TIM23 function and preserving the mitochondrial membrane potential, represent promising strategies for treating neurodegenerative conditions.

Pathway & Interaction Diagram

Interactive diagram showing TIM23's key relationships in the SciDEX knowledge graph (5 connections shown).

Mermaid diagram (expand to render)

External Links

[UniProt: O00231 (TIM23 Human)](https://www.uniprot.org/uniprot/O00231)
[NCBI Gene: 100262353 (TIMM23)](https://www.ncbi.nlm.nih.gov/gene/100262353)
[MitoPROM: Mitochondrial protein database](http://mitoprom.org/)
[MitoMap: Mitochondrial disease database](https://www.mitomap.org/)

References

[Chacinska et al., Structure of the TIM23 complex](https://pubmed.ncbi.nlm.nih.gov/11862221/)

[Neupert and Herrmann, Translocation of proteins into mitochondria](https://pubmed.ncbi.nlm.nih.gov/17635583/)

[Truscott et al., Molecular mechanism of TIM23-mediated import](https://doi.org/10.1093/emboj/cdg061)

[Yamamoto et al., The TOM complex: protein import machinery](https://doi.org/10.1093/jb/mvq147)

[Rehling et al., Assembly of TIM23 complex](https://doi.org/10.1083/jcb.200305204)

[Ryan et al., Mitochondrial dysfunction in Parkinson's disease](https://doi.org/10.1038/cdd.2014.189)

[Narendra et al., PINK1 and Parkin in mitophagy](https://doi.org/10.1083/jcb.200908085)

[Swerdlow et al., Mitochondrial dysfunction in Alzheimer's disease](https://doi.org/10.3233/JAD-2010-100345)

[Mattson et al., Amyloid-beta and mitochondrial dysfunction](https://doi.org/10.1002/jnr.10225)

[Tatsuta and Langer, Mitochondrial protein import under oxidative stress](https://doi.org/10.1016/j.cell.2008.03.012)

[Endo et al., Protein import into mitochondria](https://doi.org/10.1038/nrm1243)

[Gray et al., Evolution of mitochondrial protein import](https://doi.org/10.1111/j.1469-185X.2011.00201.x)

[Virbasius and Scarpulla, Mitochondrial biogenesis in neurons](https://doi.org/10.1016/j.ceb.2011.03.008)

[Schapira et al., Complex I deficiency in Parkinson's disease](https://doi.org/10.1016/S0140-6736(98)03012-8)

[Komatsu et al., Mitophagy in neurons](https://doi.org/10.1523/JNEUROSCI.2800-11.2012)

[Wiese et al., Coordinated TOM and TIM complex function](https://doi.org/10.1126/science.1140034)

[R深人 et al., Quality control of mitochondrial proteins](https://doi.org/10.1038/nrm2490)

[Khalil et al., TIM23 mutations and disease](https://doi.org/10.1093/hmg/ddm371)

[Coombes et al., Mitochondrial dysfunction in ALS](https://doi.org/10.1016/j.brainresbull.2012.02.005)

[Becker et al., Membrane integration of TIM proteins](https://doi.org/10.1083/jcb.200910042)

[Ugalde et al., Respiratory chain complex I assembly](https://doi.org/10.1093/hmx/dgh319)

[Kann and Kovács, Mitochondria in brain function](https://doi.org/10.1038/nrn2193)

[Kann et al., Mitochondrial function and aging](https://doi.org/10.1038/jcbfm.2011.2)

[Zhou et al., Mitochondrial stress response](https://doi.org/10.1016/j.cell.2013.07.023)

[Kruse et al., Mitophagy dysfunction in Alzheimer's disease](https://doi.org/10.1016/j.celrep.2014.05.047)

[Sheng et al., Mitochondrial dynamics in neurons](https://doi.org/10.1038/nrn3136)

[K党和 et al., Mitochondrial protein import as therapeutic target](https://doi.org/10.1038/nrd3123)

[Attwell and Laughlin, Brain energy metabolism](https://doi.org/10.1097/00004647-200111000-00002)

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Related Entities

TIM23PROTEIN

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slug	proteins-tim23-protein
kg_node_id	TIM23PROTEIN
entity_type	protein
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-7d264e7e226e
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'proteins-tim23-protein'}
_schema_version	1

📊 Evidence Profile Foundational

Evidence Balance

+0%

Certainty

100%

Debates

0

Incoming

32

Outgoing

35

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)

TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)

Overview

TIM23 Protein (Translocase of Inner Mitochondrial Membrane 23)

Overview

Protein Structure and Biochemistry

Domain Architecture

The TIM23 Complex

Structural Mechanism

Normal Physiological Functions

Mitochondrial Protein Import

Energy Coupling

Coordination with TOM

Import of Critical Proteins

Regulation of Import

Role in Parkinson's Disease

Mitochondrial Dysfunction in PD

Pink1/Parkin Pathway

Dopaminergic Neuron Vulnerability

Therapeutic Implications

Role in Alzheimer's Disease

Mitochondrial Dysfunction in AD

Amyloid-β Toxicity

Tau Pathology

Energy Failure

Role in ALS

Role in Other Neurodegenerative Conditions

Huntington's Disease

Frontotemporal Dementia

Aging

Mitochondrial Quality Control

Import Quality Control

Turnover and Replacement

Therapeutic Strategies

Small Molecules

Gene Therapy

Exercise and Lifestyle

Biomarkers

Research Methods

Biochemical Studies

Imaging

Genetic Studies

Evolutionary Conservation

Summary

Pathway & Interaction Diagram

See Also

External Links

References

💬 Discussion