Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0030943 mitochondrion targeting sequence binding	IBA GO_REF:0000033	ACCEPT	Summary: TOMM40 forms the channel that translocates presequence-containing precursors. The beta-barrel pore interacts with targeting sequences during translocation. Well supported by yeast Tom40 studies and human data (PMID:15644312).
GO:0030150 protein import into mitochondrial matrix	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: TOMM40 is the central channel through which matrix-destined preproteins pass. However, TOMM40 is involved in ALL mitochondrial import pathways, not only matrix import. This annotation captures only one pathway (TOM-TIM23-PAM). Reason: Matrix import is one of several import routes through the TOM channel.
GO:0005742 mitochondrial outer membrane translocase complex	IBA GO_REF:0000033	ACCEPT	Summary: TOMM40 is the defining channel subunit of the TOM complex. Directly demonstrated in human cells by co-immunoprecipitation and BN-PAGE (PMID:12198123, PMID:15644312, PMID:18331822).
GO:0008320 protein transmembrane transporter activity	IBA GO_REF:0000033	ACCEPT	Summary: TOMM40 is the protein-conducting channel of the outer membrane. This MF term accurately describes its core molecular function. Supporting Evidence: file:human/TOMM40/TOMM40-deep-research-falcon.md Primary molecular function: Tom40 (TOMM40 product) is a β‑barrel translocation pore in the mitochondrial outer membrane that enables import of nuclear-encoded mitochondrial precursor proteins into mitochondria as part of the TOM complex.
GO:0008320 protein transmembrane transporter activity	IEA GO_REF:0000002	ACCEPT	Summary: Redundant with IBA annotation for the same term. InterPro-based inference is correct — TOMM40 has protein transmembrane transporter activity.
GO:0030150 protein import into mitochondrial matrix	IEA GO_REF:0000002	KEEP AS NON CORE	Summary: Redundant with IBA for same term. Correct but captures only one of several import pathways through TOM. Reason: Matrix import is one specific pathway; TOMM40 serves all import routes.
GO:0055085 transmembrane transport	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Very generic parent term. The more specific GO:0008320 (protein transmembrane transporter activity) is already annotated and more informative. Reason: Too general; subsumed by more specific annotations.
GO:0005515 protein binding	IPI PMID:31412244 TOM40 Targets Atg2 to Mitochondria-Associated ER Membranes f...	REMOVE	Summary: PMID:31412244 shows TOM40 targets Atg2 to MAM for phagophore expansion. Protein binding is uninformative per curation guidelines. The actual function is recruitment of ATG2A to ER-mitochondria contact sites. Reason: Protein binding is uninformative. The interaction with ATG2A represents a non-core MAM/autophagy function.
GO:0030150 protein import into mitochondrial matrix	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: Redundant with IBA and IEA for same term. Correct but non-core — matrix import is one of many pathways served by the TOM channel.
GO:0005739 mitochondrion	IDA GO_REF:0000052	MARK AS OVER ANNOTATED	Summary: Correct but too general — TOMM40 specifically localizes to the mitochondrial outer membrane. The more specific CC term GO:0005741 is already annotated. Reason: Subsumed by more specific mitochondrial outer membrane annotation.
GO:0005741 mitochondrial outer membrane	EXP PMID:15644312 Dissection of the mitochondrial import and assembly pathway ...	ACCEPT	Summary: Humphries et al. 2005 demonstrated TOMM40 localization to the outer membrane by subcellular fractionation and protease protection assays. Core CC.
GO:0005741 mitochondrial outer membrane	EXP PMID:31206022 BAP31 regulates mitochondrial function via interaction with ...	ACCEPT	Summary: Namba 2019 confirmed TOMM40 at OM via immunofluorescence and co-IP. Redundant with PMID:15644312 evidence for same term.
GO:0030150 protein import into mitochondrial matrix	IMP PMID:15644312 Dissection of the mitochondrial import and assembly pathway ...	KEEP AS NON CORE	Summary: Humphries et al. showed depletion of TOMM40 compromises protein import. However, this is expected for the general import channel. Non-core because TOMM40 serves all import routes, not specifically matrix import.
GO:0005741 mitochondrial outer membrane	NAS PMID:18331822 Identification of Tom5 and Tom6 in the preprotein translocas...	ACCEPT	Summary: Kato & Mihara 2008 identified Tom5 and Tom6 in the human TOM complex and confirmed Tom40 as an outer membrane component. Redundant with EXP evidence.
GO:0045040 protein insertion into mitochondrial outer membrane	NAS PMID:18331822 Identification of Tom5 and Tom6 in the preprotein translocas...	MODIFY	Summary: This term refers to insertion of proteins INTO the outer membrane (e.g., alpha-helical or beta-barrel proteins). TOMM40 itself is inserted into the OM but does not catalyze insertion of others — that is the role of SAM (for beta-barrels) and MTCH2/MIM (for alpha-helical proteins). TOMM40 facilitates translocation THROUGH the outer membrane, not insertion into it. Reason: TOMM40 is a translocation channel, not an insertase. It translocates proteins across the OM, not into the OM lipid bilayer. Proposed replacements: protein transmembrane transporter activity
GO:0140596 TOM complex	NAS PMID:18331822 Identification of Tom5 and Tom6 in the preprotein translocas...	ACCEPT	Summary: Kato & Mihara confirmed TOMM40 in the human TOM complex via immuno-isolation. GO:0140596 (TOM complex) is a more specific CC term than GO:0005742 (mitochondrial outer membrane translocase complex). Both are correct.
GO:0005739 mitochondrion	HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an...	MARK AS OVER ANNOTATED	Summary: High-throughput mitochondrial proteome confirms TOMM40 as mitochondrial. Too general — more specific OM annotation exists. Reason: Subsumed by mitochondrial outer membrane annotation.
GO:0005515 protein binding	IPI PMID:31206022 BAP31 regulates mitochondrial function via interaction with ...	REMOVE	Summary: Namba 2019 showed TOMM40 interacts with BCAP31 at ER-mitochondria contact sites. Protein binding is uninformative per guidelines. Reason: Protein binding is uninformative. The BCAP31 interaction is a non-core MAM function.
GO:0044233 mitochondria-associated endoplasmic reticulum membrane contact site	IDA PMID:31206022 BAP31 regulates mitochondrial function via interaction with ...	KEEP AS NON CORE	Summary: Namba 2019 demonstrated TOMM40 localizes to MAM via interaction with BCAP31. This is a secondary localization beyond its primary OM residence. The MAM function (facilitating Complex I assembly) is a non-core role. Reason: MAM localization is secondary to the core TOM complex function.
GO:0070585 protein localization to mitochondrion	IGI PMID:31206022 BAP31 regulates mitochondrial function via interaction with ...	KEEP AS NON CORE	Summary: Namba 2019 showed BAP31-TOMM40 complex mediates NDUFS4 translocation to mitochondria. This is a specific aspect of TOMM40 general import function. The term is quite general but captures TOMM40 role in protein localization. Reason: General term; the specific Complex I assembly role via BAP31 is non-core.
GO:0005743 mitochondrial inner membrane	IDA PMID:24746669 Cyclin B1/Cdk1 coordinates mitochondrial respiration for cel...	REMOVE	Summary: PMID:24746669 is about Cyclin B1/Cdk1 and mitochondrial respiration. TOMM40 is an outer membrane beta-barrel protein. Inner membrane localization is incorrect — TOMM40 may contact the IM via supercomplex formation with TIM complexes, but it is not an IM resident protein. Reason: TOMM40 is an outer membrane protein. Inner membrane annotation is incorrect; likely an artifact of co-fractionation.
GO:0005515 protein binding	IPI PMID:27554484 Tim29 is a novel subunit of the human TIM22 translocase and ...	REMOVE	Summary: Kang et al. 2016 showed TIMM29 interacts with TOMM40, linking TIM22 to TOM complex. Protein binding is uninformative per guidelines. Reason: Protein binding is uninformative. The TIM22-TOM interaction via TIMM29 is better captured by TOM complex CC annotation.
GO:0005741 mitochondrial outer membrane	TAS Reactome:R-HSA-5205661	ACCEPT	Summary: Reactome pathway for PINK1 recruitment to mitochondria. Confirms TOMM40 at the outer membrane. Redundant with direct experimental evidence.
GO:0016020 membrane	IDA PMID:15644312 Dissection of the mitochondrial import and assembly pathway ...	MARK AS OVER ANNOTATED	Summary: Extremely generic CC term. TOMM40 is specifically in the mitochondrial outer membrane (GO:0005741), which is already well-annotated. Reason: Too general; subsumed by mitochondrial outer membrane.
GO:0008320 protein transmembrane transporter activity	ISS GO_REF:0000024	ACCEPT	Summary: Ortholog-based transfer of transporter activity. Correct and redundant with IBA evidence for same term.
GO:0005739 mitochondrion	IMP NOT PMID:11745481 Genetic identity and differential expression of p38.5 (Hayma...	REMOVE	Summary: PMID:11745481 (Das et al. 2001) identified TOMM40 as p38.5/Haymaker and reported differential expression in malignant cells. The NOT annotation for mitochondrion localization is incorrect — TOMM40 is definitively a mitochondrial protein. This may reflect early confusion about the gene identity. Reason: The NOT\|mitochondrion annotation contradicts overwhelming evidence that TOMM40 is a core mitochondrial outer membrane protein.
GO:0005741 mitochondrial outer membrane	ISS PMID:10980201 Characterization of rat TOM40, a central component of the pr...	ACCEPT	Summary: Based on rat Tom40 characterization (Suzuki et al. 2000). Correct — outer membrane localization is conserved.
GO:0005742 mitochondrial outer membrane translocase complex	IDA PMID:12198123 Insertion and assembly of human tom7 into the preprotein tra...	ACCEPT	Summary: Johnston et al. 2002 identified TOMM40 in the ~380 kDa TOM complex by BN-PAGE and supershift analysis. Direct experimental evidence for TOM complex membership.
GO:0005742 mitochondrial outer membrane translocase complex	IDA PMID:15644312 Dissection of the mitochondrial import and assembly pathway ...	ACCEPT	Summary: Humphries et al. 2005 confirmed TOMM40 in TOM complex by BN-PAGE. Redundant with PMID:12198123 but independent confirmation.
GO:0008320 protein transmembrane transporter activity	TAS PMID:15644312 Dissection of the mitochondrial import and assembly pathway ...	ACCEPT	Summary: Humphries et al. described TOMM40 as the channel-forming subunit essential for protein import. Core MF annotation.

Core Functions

TOMM40 is the central beta-barrel channel of the TOM complex, the main entry gate for nuclear-encoded mitochondrial precursor proteins. Two copies of TOMM40 form a dimeric pore in the outer membrane through which virtually all imported proteins pass, regardless of their final destination (matrix, inner membrane, IMS, or outer membrane). The channel interacts with mitochondrial targeting sequences during translocation.

Molecular Function:

protein transmembrane transporter activity

Directly Involved In:

protein import into mitochondrial matrix protein import into mitochondrial intermembrane space

Cellular Locations:

mitochondrial outer membrane

In Complex:

mitochondrial outer membrane translocase complex

Supporting Evidence:

PMID:15644312
Tom40 is the channel-forming subunit of the translocase of the mitochondrial outer membrane (TOM complex), essential for protein import into mitochondria.
PMID:12198123
We found that the 120-kDa complex contains Tom40 and lacks receptor components. This intermediate can be chased to the stable approximately 380-kDa mammalian TOM complex that additionally contains Tom22.
file:human/TOMM40/TOMM40-deep-research-falcon.md
**Primary molecular function:** Tom40 (TOMM40 product) is a **β‑barrel translocation pore** in the mitochondrial outer membrane that enables **import of nuclear-encoded mitochondrial precursor proteins** into mitochondria as part of the TOM complex.

References

file:human/TOMM40/TOMM40-deep-research-falcon.md

Falcon deep research report for TOMM40

Falcon corroborates TOMM40 as the beta-barrel TOM complex pore in the mitochondrial outer membrane and separates this core import function from less direct APOE-region disease association signals.

"**Primary molecular function:** Tom40 (TOMM40 product) is a **β‑barrel translocation pore** in the mitochondrial outer membrane that enables **import of nuclear-encoded mitochondrial precursor proteins** into mitochondria as part of the TOM complex."

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000024

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000052

Gene Ontology annotation based on curation of immunofluorescence data

PMID:10980201

Characterization of rat TOM40, a central component of the preprotein translocase of the mitochondrial outer membrane.

Mammalian Tom40 is embedded in the mitochondrial outer membrane likely as a beta-barrel, lacking predicted alpha-helical transmembrane segments.

"Although it has no predictable alpha-helical transmembrane segments, OM38 is resistant to alkaline carbonate extraction and is inaccessible to proteases and polyclonal antibodies added from outside the mitochondria, suggesting that it is embedded in the membrane, probably in a beta-barrel structure"
Tom40 is a component of an ~400-kDa TOM complex, firmly associating with Tom22 and with the import receptor Tom20.

"Blue native polyacrylamide gel electrophoresis revealed that OM38 is a component of a approximately 400-kDa complex, firmly associating with rTOM22 and loosely associating with rTOM20."
Tom40 is essential for preprotein import activity of the mitochondrial outer membrane.

"The preprotein in transit to the matrix interacted with the TOM complex containing OM38, and immunodepletion of OM38 resulted in the loss of preprotein import activity of the detergent-solubilized and reconstituted outer membrane vesicles."

PMID:11745481

Genetic identity and differential expression of p38.5 (Haymaker) in human malignant and nonmalignant cells.

Identifies the p38.5 (Haymaker) protein as the chromosome-19 gene product later recognized as TOMM40, with elevated expression in malignant cells.

"Sequence analyses of these cDNA clones reveal open reading frames (ORFs) that include the previously identified 11-mer peptide from purified, native p38.5 and that have identical sequences to a gene of unknown function on chromosome 19."

PMID:12198123

Insertion and assembly of human tom7 into the preprotein translocase complex of the outer mitochondrial membrane.

In human mitochondria, newly imported Tom7 assembles into a ~120-kDa Tom40-containing intermediate that is chased into the mature ~380-kDa TOM complex upon addition of Tom22.

"We found that the 120-kDa complex contains Tom40 and lacks receptor components. This intermediate can be chased to the stable approximately 380-kDa mammalian TOM complex that additionally contains Tom22."
Tom40 is the channel-forming core of the general import pore complex that translocates preproteins into mitochondria.

"Tom7 is a component of the translocase of the outer mitochondrial membrane (TOM) and assembles into a general import pore complex that translocates preproteins into mitochondria."

PMID:15644312

Dissection of the mitochondrial import and assembly pathway for human Tom40.

TOMM40 is the channel-forming subunit of the human TOM complex and is essential for protein import into mitochondria.

"Tom40 is the channel-forming subunit of the translocase of the mitochondrial outer membrane (TOM complex), essential for protein import into mitochondria."
Hsp90 chaperones delivery of the Tom40 precursor to mitochondria in an ATP-dependent manner before its assembly via the TOM and SAM complexes.

"We identify that Hsp90 is involved in delivery of the Tom40 precursor to mitochondria in an ATP-dependent manner. The precursor then forms its first stable intermediate with the outer face of the TOM complex before its membrane integration and assembly."
Efficient assembly of human Tom40 into the mature TOM complex requires the outer membrane SAM complex (Sam50).

"we show that Tom40 assembly is reduced in mitochondria depleted of human Sam50."

PMID:18331822

Identification of Tom5 and Tom6 in the preprotein translocase complex of human mitochondrial outer membrane.

Human Tom40 is the central import channel of the TOM complex and small Tom5/Tom6/Tom7 subunits maintain the structural integrity of the complex.

"The fungal preprotein translocase of the mitochondrial outer membrane (TOM complex) comprises import receptors Tom70, Tom20, and Tom22, import channel Tom40, and small Tom proteins Tom5, Tom6, and Tom7"
Depletion of TOMM40 in human cells reduces the steady-state levels of all small Tom subunits, indicating Tom40 is required for their stability in the TOM complex.

"Conversely, knockdown of hTom40 decreased the level of all small Tom proteins."

PMID:24746669

Cyclin B1/Cdk1 coordinates mitochondrial respiration for cell-cycle G2/M progression.

Cited in the context of mitochondrial respiration regulation; the study shows cyclin B1/Cdk1 phosphorylates mitochondrial complex I subunits in the matrix (not a direct TOMM40 function paper).

"a fraction of cyclin B1/Cdk1 proteins localizes to the matrix of mitochondria and phosphorylates a cluster of mitochondrial proteins, including the complex I (CI) subunits in the respiratory chain."

PMID:27554484

Tim29 is a novel subunit of the human TIM22 translocase and is involved in complex assembly and stability.

TOMM40 physically interacts with Tim29 to couple the outer-membrane TOM complex to the inner-membrane TIM22 carrier translocase in human mitochondria.

"Furthermore, Tim29 contacts the Translocase of the Outer Mitochondrial Membrane, TOM complex, enabling a mechanism for transport of hydrophobic carrier substrates across the aqueous intermembrane space."
Chemical cross-linking and co-immunoprecipitation demonstrate a direct hTom40-Tim29 interaction that bridges the TIM22 and TOM complexes.

"we found hTom40 cross-linked to Tim29... these results suggest that Tim29 acts as a bridge between the TIM22 and TOM complexes."

PMID:31206022

BAP31 regulates mitochondrial function via interaction with Tom40 within ER-mitochondria contact sites.

TOMM40 interacts with the ER membrane protein BAP31 at ER-mitochondria contact sites to facilitate import of the complex I subunit NDUFS4.

"BAP31 interacts with mitochondria-localized proteins, including Tom40, to stimulate the translocation of NDUFS4, the component of complex I from the cytosol to the mitochondria."
Disruption of the BAP31-Tom40 bridging complex impairs mitochondrial complex I activity and oxygen consumption due to reduced NDUFS4 import.

"Disruption of the BAP31-Tom40 complex inhibits mitochondrial complex I activity and oxygen consumption by the decreased NDUFS4 localization to the mitochondria."

PMID:31412244

TOM40 Targets Atg2 to Mitochondria-Associated ER Membranes for Phagophore Expansion.

TOMM40 directly binds the autophagy lipid-transfer protein Atg2A via its C-terminal MAM localization domain, recruiting Atg2A to mitochondria- associated ER membranes during phagophore expansion.

"Proteomic analysis identifies the outer mitochondrial membrane protein TOM40 as a MLD-interacting partner. The Atg2A-TOM40 interaction is responsible for MAM localization of Atg2A and requires the TOM receptor protein TOM70."
The TOM70-TOM40 complex recruits Atg2A to the MAM to enable lipid transfer for autophagosome expansion.

"we propose a model that the TOM70-TOM40 complex recruits Atg2A to the MAM for vesicular and/or non-vesicular lipid transport into the expanding phagophore to grow the size of autophagosomes for efficient autophagic flux."

PMID:34800366

Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context.

TOMM40 is included in the high-confidence human mitochondrial proteome (MitoCoP), confirming its mitochondrial localization as a translocase subunit.

"We classified >8,000 proteins in mitochondrial preparations of human cells and defined a mitochondrial high-confidence proteome of >1,100 proteins (MitoCoP). We identified interactors of translocases, respiratory chain, and ATP synthase assembly factors."

Reactome:R-HSA-5205661

Pink1 is recruited from the cytoplasm to the mitochondria

Deep Research

Falcon

(TOMM40-deep-research-falcon.md)

Research Report: Human **TOMM40** (UniProt **O96008**) — Functional Annotation, Mechanism, and Disease-Linked Evidence (2023–2024 prioritized) Falcon Edison Scientific Literature 28 citations 2026-05-11T00:07:58.383091

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research Report: Human TOMM40 (UniProt O96008) — Functional Annotation, Mechanism, and Disease-Linked Evidence (2023–2024 prioritized)

1. Target verification (identity, organism, family/domain alignment)

The literature retrieved and analyzed consistently refers to human TOMM40 (Tom40) as the pore-forming β‑barrel subunit of the mitochondrial translocase of the outer membrane (TOM) complex, matching the UniProt O96008 description (“mitochondrial import receptor subunit TOM40 homolog”) and its porin/β‑barrel domain architecture. Tom40 is described as a 19‑β‑strand β‑barrel channel in the mitochondrial outer membrane (OMM). (nussberger2024newinsightsinto pages 2-4, su2024structureofthe pages 3-5)

2. Key concepts and definitions (current understanding)

2.1 TOM complex and mitochondrial protein import

In human cells, the TOM complex is the primary entry gate for the vast majority of nuclear-encoded mitochondrial precursor proteins (preproteins) that must cross the outer mitochondrial membrane en route to the OMM, intermembrane space (IMS), inner membrane (IMM), or matrix. (nussberger2024newinsightsinto pages 1-2)

2.2 TOMM40/Tom40 molecular function

TOMM40 encodes Tom40, the central translocation pore of the TOM complex. Structurally, Tom40 is a β‑barrel channel (19 β‑strands) that provides the conduit for preproteins to move from cytosol into the IMS as the first step in mitochondrial import. (su2024structureofthe pages 3-5, nussberger2024newinsightsinto pages 2-4)

2.3 Receptor–pore coupling: Tom20/Tom22/Tom70

Preproteins are initially recognized by TOM receptors (classically Tom20, Tom22, Tom70), then routed to the Tom40 channel for translocation. A 2024 review summarizes that Tom20 preferentially recognizes cleavable N‑terminal presequences and Tom70 binds other precursor classes including hydrophobic carrier precursors, contextualizing how substrates are delivered to the pore. (borgert2024conservedqualitycontrol pages 3-4)

3. Subcellular localization and complex membership

3.1 Localization

Tom40 is an integral OMM protein forming the TOM pore. (su2024structureofthe pages 3-5, nussberger2024newinsightsinto pages 2-4)

3.2 Core subunits and structural organization

A 2024 cryo‑EM study of the human TOM holo complex reports the core complex composition as Tom40, Tom22, Tom5, Tom6, Tom7, with receptor Tom20 positioned asymmetrically on the complex. (su2024structureofthe pages 3-5)

A key structural view of the human TOM holo complex subunit arrangement (Tom40/Tom22/Tom5/Tom6/Tom7) is provided in Figure 1 of Su et al. 2024. (su2024structureofthe media 4747d2ba)

4. Recent developments (prioritizing 2023–2024)

4.1 High-resolution structural insights into human TOM/Tom40 (2024)

A 2024 expert review synthesizing recent sub‑nanometer to near‑atomic structures reports that Tom40 is a 19‑β‑strand β‑barrel and that human TOM core structures show two Tom40 pores that create a cytosolic-side “preprotein funnel”. The review cites a human TOM core complex at 2.53 Å resolution (PDB 7VD2) and notes Tom40 dimerization involves β1–β19 interactions (analogous to VDAC). (nussberger2024newinsightsinto pages 2-4)

4.2 Structural plasticity and receptor positioning (Tom20) in the human TOM holo complex (Su et al., 2024)

Su et al. determined a cryo‑EM structure of the human TOM holo complex including an intact Tom20 receptor (PNAS Nexus; June 2024, https://doi.org/10.1093/pnasnexus/pgae269). Tom20 was resolved as a single subunit located near the center of the complex and stabilized by interactions with Tom22, Tom40, and Tom6. (su2024structureofthe pages 3-5)

The structure supports a model in which receptor positioning and TOM architecture allow simultaneous receptor engagement for efficient preprotein delivery into Tom40. Tom20 binding is associated with conformational changes in Tom22 (reported shifts/displacements on the order of a few Å), consistent with a dynamic, plastic receptor–pore interface. (su2024structureofthe pages 3-5)

4.3 Mechanistic open questions and emerging models (2024)

Despite structural advances, a 2024 review emphasizes that there is still no general physical model for how diverse unfolded polypeptides cross the outer membrane pore and overcome entropic/energetic barriers, especially since the OMM lacks a strong membrane potential. The review highlights hypotheses in which downstream IMS/IMM import machineries can provide pulling forces and mtHsp70 ATP hydrolysis contributes to driving matrix import. (nussberger2024newinsightsinto pages 1-2)

5. Pathways, interaction partners, and functional context

5.1 TOM–TIM coupling and downstream import routes

The TOM complex is functionally coupled to downstream translocases that determine ultimate destination (IMM/matrix/IMS). Recent synthesis highlights evidence for direct TOM interactions with the IMM translocase TIM23 during matrix translocation, reinforcing that Tom40 acts as the upstream pore for multiple import pathways. (nussberger2024newinsightsinto pages 1-2)

5.2 Quality control at the TOM pore (import stress, clogging, UPS)

A 2024 review of mitochondrial import quality control describes how import can stall and clog TOM, triggering cytosolic proteotoxic stress. It emphasizes conserved mechanisms coupling the TOM machinery to the ubiquitin–proteasome system to remove arrested precursors and maintain import competence. Although not TOMM40-specific at residue-level, this review provides mechanistic context for Tom40 as the pore whose occupancy and clearance are central to import surveillance. (borgert2024conservedqualitycontrol pages 3-4)

6. Current applications and real-world implementations

6.1 Structural biology as a platform for mechanistic inference

The 2024 human TOM holo-complex cryo‑EM structure provides a concrete framework for interpreting how receptors (e.g., Tom20) interact with Tom40 and other core subunits, enabling hypothesis-driven studies (e.g., mutagenesis of receptor–pore interfaces) relevant to mitochondrial biogenesis and import regulation. (su2024structureofthe pages 3-5, su2024structureofthe media 4747d2ba)

6.2 TOMM40 genetic variation used in clinical-trial stratification (TOMMORROW)

The TOMMORROW study (a phase 3 trial program) used TOMM40 rs10524523 (“523” poly‑T length) together with APOE genotype to stratify cognitively normal older adults into AD risk groups. A 2024 analysis leveraging TOMMORROW trial data reports enrollment of 3,465 participants aged 65–83 (trial conducted 2013–2018; ClinicalTrials.gov identifier NCT01931566 is noted in the paper). This illustrates real-world implementation of TOMM40 variation in longitudinal cognitive research and trial design. (mahedy2024investigationofgenetic pages 1-2)

7. Expert opinions and authoritative analyses (selected 2024 sources)

7.1 TOM complex as a dynamic, mechanistically unresolved but structurally tractable gateway

The Biochemical Society Transactions review (April 2024; https://doi.org/10.1042/bst20231236) frames current expert consensus: TOM is the essential OMM gateway, but critical mechanistic questions remain about capture/translocation energetics and how pore dynamics and membrane environment regulate import. (nussberger2024newinsightsinto pages 1-2, nussberger2024newinsightsinto pages 2-4)

7.2 TOMM40 within the APOE locus: interpretation cautions

A 2024 Nature Genetics autopsy-based analysis highlights how association signals within the broader APOE region often resolve to APOE ε effects after adjustment, emphasizing interpretive challenges when assigning causality to TOMM40 from common-variant GWAS in this locus. (shade2024gwasofmultiple pages 2-3)

8. Disease associations: Alzheimer’s disease locus evidence (2023–2024 prioritized)

8.1 Autopsy-based neuropathology GWAS suggests limited TOMM40-independent signal after APOE adjustment (2024)

A large autopsy-based GWAS of 11 neuropathology endophenotypes (NACC/ROSMAP/ACT; n = 7,804 total autopsied participants) evaluated multiple phenotypes (amyloid plaques, Braak stage, CAA, CERAD score, LATE-NC, etc.). APOE itself (rs429358) was the top variant in the APOE region for multiple phenotypes, but after adjusting for APOE ε diplotypes, rs429358 was no longer associated with the five APOE-linked neuropathology phenotypes; no other variants remained genome-wide significant for the other APOE-associated phenotypes, while one locus (lead variant rs7247551, between APOC2 and CLPTM1) remained significantly associated with CAA (OR = 0.81; P = 8.0 × 10−12). These results support the interpretation that, for these neuropathology endpoints, many regional signals are driven by APOE ε rather than clearly separable TOMM40 effects. (shade2024gwasofmultiple pages 2-3, shade2024gwasofmultiple pages 1-2)

8.2 Proteome-wide association implicates TOMM40 as part of an AD dementia risk network (2024)

A 2024 American Journal of Human Genetics study developed an omnibus proteome-wide association framework (PWAS‑O) and applied it to AD dementia using dorsolateral prefrontal cortex proteomic reference data. The authors report 43 PWAS risk genes and note a connected protein interaction network including well-known AD risk genes TOMM40 and neighbors in the APOE region. They report validation of causal genetic effects mediated through proteome abundance for 27/43 (63%) PWAS‑O risk genes. (hu2024omnibusproteomewideassociation pages 1-3, hu2024omnibusproteomewideassociation pages 6-7)

8.3 APOE-genotype-stratified epigenetics highlights TOMM40 CpG differences but not clear expression mediation (2024)

A 2024 Translational Psychiatry study analyzed methylation in 2,021 blood samples and 697 brain samples and found multiple APOE-region CpG differences between APOE ε4 carriers and non-carriers. In brain, the most significant APOE-region CpG was located in TOMM40 (cg02613937) and was hypomethylated in ε4 carriers (P = 1.3 × 10−13 in total sample; evidence largely from AD cases P = 7.0 × 10−13). However, the authors report this TOMM40 CpG was not significantly associated with expression of genes in the APOE region in brain, complicating a direct mechanistic interpretation. (panitch2024apoegenotypespecificmethylation pages 4-5, panitch2024apoegenotypespecificmethylation pages 1-2)

8.4 Linkage disequilibrium (LD) patterns constrain “independence” claims for TOMM40 polymorphisms

Whole-genome sequencing-based analysis of TOMM40′523 genotyping reports LD relationships showing that the APOE ε4 marker rs429358 can have high LD with TOMM40′523 haplotypes (example r2 ~0.869 reported) and that rs2075650 shows more moderate LD with a 523 haplotype (example r2 ~0.421 reported). These data support the widely recognized challenge that many common-variant signals in TOMM40/APOE are difficult to disentangle without careful conditional/haplotype analyses. (vialle2025genotypingtomm40′523 pages 20-22)

9. Relevant statistics and data highlights (from retrieved studies)

Human TOM holo complex cryo‑EM (Jun 2024): overall ~6.87 Å; local resolution ~5.6 Å for core and ~4.7 Å for Tom20-containing region; Tom20 present as one copy and positioned centrally with extensive interactions to Tom22/Tom40/Tom6. (su2024structureofthe pages 3-5)
Autopsy neuropathology GWAS (Nature Genetics, 2024): n = 7,804 autopsied participants; after APOE ε adjustment, only rs7247551 remained significant for CAA (OR = 0.81; P = 8.0 × 10−12). (shade2024gwasofmultiple pages 2-3)
Methylation study (Translational Psychiatry, 2024): 2,021 blood samples, 697 brain samples; TOMM40 CpG cg02613937 P = 1.3 × 10−13 (total brain sample) and P = 7.0 × 10−13 (AD cases). (panitch2024apoegenotypespecificmethylation pages 4-5)
TOMMORROW trial cohort used for longitudinal cognitive-change GWAS (Translational Psychiatry, 2024): 3,465 cognitively healthy adults aged 65–83, with APOE and TOMM40′523 used for risk grouping. (mahedy2024investigationofgenetic pages 1-2)

10. Summary table of evidence (2023–2024 focus)

The following table consolidates the main functional, structural, and disease-association evidence used in this report.

Topic	Key finding	System/approach	Quantitative details (resolution, sample size, p-values, OR, etc.)	Publication (first author, year, journal)	URL/DOI	Citation ID
structure/function	Human TOMM40 (Tom40) is the core pore-forming subunit of the TOM complex and forms the channel for mitochondrial preprotein translocation; the human TOM core is arranged as a dimer with two Tom40 β-barrels plus Tom22, Tom5, Tom6, and Tom7.	Cryo-EM structure of human TOM holo/core complex	Overall map ~6.87 Å; local resolution ~5.6 Å for core and ~4.7 Å for Tom20-containing region; two Tom40 pores visible in binocular-like dimeric assembly	Su, 2024, PNAS Nexus	https://doi.org/10.1093/pnasnexus/pgae269	(su2024structureofthe pages 3-5, su2024structureofthe media 4747d2ba)
structure/function	Tom40 is a 19-β-strand β-barrel pore-forming subunit; high-resolution structures show two Tom40 barrels forming a cytosolic “preprotein funnel.”	Review synthesizing recent cryo-EM/structural work on TOM	Human TOM core cited at 2.53 Å (PDB 7VD2); Tom40 dimer interface involves β1 and β19 strands	Nussberger, 2024, Biochemical Society Transactions	https://doi.org/10.1042/bst20231236	(nussberger2024newinsightsinto pages 2-4)
mechanism	TOM is the main outer-membrane entry gate for nuclear-encoded mitochondrial proteins destined for outer membrane, intermembrane space, inner membrane, or matrix; energetic/mechanical aspects remain incompletely resolved because the outer membrane lacks a strong membrane potential.	Expert review	Import is proposed to be assisted by pulling forces from IMS/IMM machineries and mtHsp70 ATP hydrolysis for matrix import	Nussberger, 2024, Biochemical Society Transactions	https://doi.org/10.1042/bst20231236	(nussberger2024newinsightsinto pages 1-2)
mechanism	Tom20 docks asymmetrically on the human TOM holo complex and contacts Tom40, Tom22, and Tom6, supporting receptor-guided substrate delivery into the Tom40 pore.	Cryo-EM with chemical cross-linking to stabilize Tom20 in human TOM	Tom20 induces conformational shifts in Tom22 (~4.4 Å C-terminus, ~3.6 Å N-terminus displacement)	Su, 2024, PNAS Nexus	https://doi.org/10.1093/pnasnexus/pgae269	(su2024structureofthe pages 3-5)
localization	TOMM40 localizes to the mitochondrial outer membrane as the central channel of the TOM translocase.	Structural review and primary structural study	Outer-membrane β-barrel channel; two-pore TOM core architecture	Nussberger, 2024, Biochemical Society Transactions; Su, 2024, PNAS Nexus	https://doi.org/10.1042/bst20231236 ; https://doi.org/10.1093/pnasnexus/pgae269	(su2024structureofthe pages 3-5, nussberger2024newinsightsinto pages 2-4)
interactions	Key TOMM40 partners in the human TOM complex include Tom22 and the small TOM proteins Tom5, Tom6, and Tom7; receptor Tom20 engages one side of the complex.	Cryo-EM structural mapping	Figure-level structural assignment of Tom40/Tom22/Tom5/Tom6/Tom7 arrangement in human holo complex	Su, 2024, PNAS Nexus	https://doi.org/10.1093/pnasnexus/pgae269	(su2024structureofthe media 4747d2ba)
quality control	The vast majority of mitochondrial proteins pass through the TOM complex, and clogged import channels are cleared by conserved quality-control mechanisms linked to the ubiquitin-proteasome system.	Review of mitochondrial import surveillance	Human cells estimated to import ~900–1300 proteins via mitochondrial pathways; clogged precursors trigger proteotoxic stress and require extraction/degradation pathways	Borgert, 2024, Journal of Inherited Metabolic Disease	https://doi.org/10.1002/jimd.12756	(borgert2024conservedqualitycontrol pages 3-4)
disease genetics	In a large autopsy-based GWAS of neuropathology endophenotypes, most APOE-region signals were accounted for by APOE ε diplotypes rather than independent TOMM40 effects.	GWAS/meta-analysis of neuropathology endophenotypes across NACC, ROSMAP, ACT	n = 7,804 autopsied participants total; after APOE adjustment, rs429358 lost significance for five phenotypes; only rs7247551 (between APOC2 and CLPTM1) remained significant for CAA, OR = 0.81, P = 8.0 × 10^-12	Shade, 2024, Nature Genetics	https://doi.org/10.1038/s41588-024-01939-9	(shade2024gwasofmultiple pages 2-3, shade2024gwasofmultiple pages 1-2)
disease proteomics	PWAS-O identified TOMM40 among 43 AD dementia risk genes, supporting a genetically regulated proteome-level link at the APOE/TOMM40 region.	Omnibus proteome-wide association study using DLPFC proteomics integrated with AD GWAS	43 PWAS risk genes identified; 27/43 (63%) showed validated causal genetic effects mediated through the proteome	Hu, 2024, American Journal of Human Genetics	https://doi.org/10.1016/j.ajhg.2024.07.001	(hu2024omnibusproteomewideassociation pages 1-3, hu2024omnibusproteomewideassociation pages 6-7)
disease epigenetics	In brain, the strongest APOE-genotype-associated CpG in the APOE region was in TOMM40, hypomethylated in APOE ε4 carriers, but this CpG was not significantly associated with expression of APOE-region genes in brain.	Genome-wide methylation analysis in blood and brain	2,021 blood samples and 697 brain samples; TOMM40 cg02613937 in brain: total sample P = 1.3 × 10^-13, AD cases P = 7.0 × 10^-13; 7 APOE-region CpGs reached P < 5 × 10^-8 between ε4 carriers and non-carriers	Panitch, 2024, Translational Psychiatry	https://doi.org/10.1038/s41398-024-02834-x	(panitch2024apoegenotypespecificmethylation pages 4-5, panitch2024apoegenotypespecificmethylation pages 1-2)
disease/cognition	The TOMMORROW trial embedded TOMM40 rs10524523 (“523”) with APOE genotype in risk stratification for cognitively normal older adults, reflecting ongoing real-world use of TOMM40 variation in longitudinal cognitive studies.	Clinical-trial cohort design for longitudinal cognition GWAS	Trial enrolled 3,465 adults aged 65–83 years; TOMM40 “523” used with APOE ε2/3/4 to classify high vs low AD risk groups	Mahedy, 2024, Translational Psychiatry	https://doi.org/10.1038/s41398-023-02726-6	(mahedy2024investigationofgenetic pages 1-2)
disease genetics/interpretation	Recent reviews of AD/CVD shared genetics still place TOMM40 within the broader APOE locus rather than establishing TOMM40 as an unequivocally independent causal AD gene.	Scoping review of genetic overlap literature	2,918 articles screened; 274 included; authors emphasize shared loci/mechanisms but limitations in longitudinal and diverse cohorts	Moore, 2024, Genes	https://doi.org/10.3390/genes15121509	(moore2024istherelationship pages 1-2)

Table: This table compiles the main 2023-2024 structural, mechanistic, localization, quality-control, and disease-association evidence for human TOMM40/Tom40. It is useful for separating well-supported core mitochondrial import functions from more ambiguous disease-genetics signals at the APOE locus.

11. Practical functional annotation (concise)

Primary molecular function: Tom40 (TOMM40 product) is a β‑barrel translocation pore in the mitochondrial outer membrane that enables import of nuclear-encoded mitochondrial precursor proteins into mitochondria as part of the TOM complex. (su2024structureofthe pages 3-5, nussberger2024newinsightsinto pages 2-4)

Cellular location: Mitochondrial outer membrane (integral membrane β‑barrel). (su2024structureofthe pages 3-5, nussberger2024newinsightsinto pages 2-4)

Core pathway membership: Mitochondrial protein import via TOM, coordinating with downstream translocases such as TIM23 for matrix-directed import. (nussberger2024newinsightsinto pages 1-2)

Key interaction partners (complex subunits): Tom22, Tom5, Tom6, Tom7 (core); receptor Tom20 docks and contacts Tom40/Tom22/Tom6. (su2024structureofthe pages 3-5, su2024structureofthe media 4747d2ba)

Disease interpretation (AD locus): TOMM40 is repeatedly implicated in APOE-region multi-omics analyses, but autopsy-based neuropathology genetics indicates many signals in this locus are largely accounted for by APOE ε effects after adjustment; LD between TOMM40 variants and APOE alleles complicates claims of TOMM40-independent causality without conditional/haplotype modeling. (shade2024gwasofmultiple pages 2-3, vialle2025genotypingtomm40′523 pages 20-22)

References

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Citations

nussberger2024newinsightsinto pages 1-2
borgert2024conservedqualitycontrol pages 3-4
su2024structureofthe pages 3-5
nussberger2024newinsightsinto pages 2-4
mahedy2024investigationofgenetic pages 1-2
shade2024gwasofmultiple pages 2-3
panitch2024apoegenotypespecificmethylation pages 4-5
moore2024istherelationship pages 1-2
shade2024gwasofmultiple pages 1-2
hu2024omnibusproteomewideassociation pages 1-3
hu2024omnibusproteomewideassociation pages 6-7
panitch2024apoegenotypespecificmethylation pages 1-2
https://doi.org/10.1093/pnasnexus/pgae269
https://doi.org/10.1042/bst20231236
https://doi.org/10.1002/jimd.12756
https://doi.org/10.1038/s41588-024-01939-9
https://doi.org/10.1016/j.ajhg.2024.07.001
https://doi.org/10.1038/s41398-024-02834-x
https://doi.org/10.1038/s41398-023-02726-6
https://doi.org/10.3390/genes15121509
https://doi.org/10.1042/bst20231236,
https://doi.org/10.1093/pnasnexus/pgae269,
https://doi.org/10.1002/jimd.12756,
https://doi.org/10.1038/s41398-023-02726-6,
https://doi.org/10.1038/s41588-024-01939-9,
https://doi.org/10.1016/j.ajhg.2024.07.001,
https://doi.org/10.1038/s41398-024-02834-x,
https://doi.org/10.3390/genes15121509,

📄 View Raw YAML

id: O96008
gene_symbol: TOMM40
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: Channel-forming subunit of the translocase of the outer mitochondrial
  membrane (TOM) complex. TOMM40 forms the central beta-barrel pore through which
  most nuclear-encoded mitochondrial precursor proteins are translocated across the
  outer membrane. The TOM complex contains two copies of TOMM40 forming a dimeric
  channel, together with receptor subunits (TOMM20, TOMM22, TOMM70) and small subunits
  (TOMM5, TOMM6, TOMM7). Also involved in ER-mitochondria contact sites via BCAP31
  interaction, and in PINK1/Parkin mitophagy signaling through TOM-VDAC2 interaction.
alternative_products:
- name: '1'
  id: O96008-1
- name: '2'
  id: O96008-2
  sequence_note: VSP_008589, VSP_008590
existing_annotations:
- term:
    id: GO:0030943
    label: mitochondrion targeting sequence binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: TOMM40 forms the channel that translocates presequence-containing precursors.
      The beta-barrel pore interacts with targeting sequences during translocation.
      Well supported by yeast Tom40 studies and human data (PMID:15644312).
    action: ACCEPT
- term:
    id: GO:0030150
    label: protein import into mitochondrial matrix
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: TOMM40 is the central channel through which matrix-destined preproteins
      pass. However, TOMM40 is involved in ALL mitochondrial import pathways, not
      only matrix import. This annotation captures only one pathway (TOM-TIM23-PAM).
    action: KEEP_AS_NON_CORE
    reason: Matrix import is one of several import routes through the TOM channel.
- term:
    id: GO:0005742
    label: mitochondrial outer membrane translocase complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: TOMM40 is the defining channel subunit of the TOM complex. Directly
      demonstrated in human cells by co-immunoprecipitation and BN-PAGE (PMID:12198123,
      PMID:15644312, PMID:18331822).
    action: ACCEPT
- term:
    id: GO:0008320
    label: protein transmembrane transporter activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: TOMM40 is the protein-conducting channel of the outer membrane. This
      MF term accurately describes its core molecular function.
    action: ACCEPT
    supported_by:
    - reference_id: file:human/TOMM40/TOMM40-deep-research-falcon.md
      supporting_text: >-
        **Primary molecular function:** Tom40 (TOMM40 product) is a **β‑barrel
        translocation pore** in the mitochondrial outer membrane that enables
        **import of nuclear-encoded mitochondrial precursor proteins** into
        mitochondria as part of the TOM complex.
- term:
    id: GO:0008320
    label: protein transmembrane transporter activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Redundant with IBA annotation for the same term. InterPro-based inference
      is correct — TOMM40 has protein transmembrane transporter activity.
    action: ACCEPT
- term:
    id: GO:0030150
    label: protein import into mitochondrial matrix
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Redundant with IBA for same term. Correct but captures only one of
      several import pathways through TOM.
    action: KEEP_AS_NON_CORE
    reason: Matrix import is one specific pathway; TOMM40 serves all import routes.
- term:
    id: GO:0055085
    label: transmembrane transport
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: Very generic parent term. The more specific GO:0008320 (protein transmembrane
      transporter activity) is already annotated and more informative.
    action: MARK_AS_OVER_ANNOTATED
    reason: Too general; subsumed by more specific annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31412244
  review:
    summary: PMID:31412244 shows TOM40 targets Atg2 to MAM for phagophore expansion.
      Protein binding is uninformative per curation guidelines. The actual function
      is recruitment of ATG2A to ER-mitochondria contact sites.
    action: REMOVE
    reason: Protein binding is uninformative. The interaction with ATG2A represents
      a non-core MAM/autophagy function.
- term:
    id: GO:0030150
    label: protein import into mitochondrial matrix
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: Redundant with IBA and IEA for same term. Correct but non-core — matrix
      import is one of many pathways served by the TOM channel.
    action: KEEP_AS_NON_CORE
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  review:
    summary: Correct but too general — TOMM40 specifically localizes to the mitochondrial
      outer membrane. The more specific CC term GO:0005741 is already annotated.
    action: MARK_AS_OVER_ANNOTATED
    reason: Subsumed by more specific mitochondrial outer membrane annotation.
- term:
    id: GO:0005741
    label: mitochondrial outer membrane
  evidence_type: EXP
  original_reference_id: PMID:15644312
  review:
    summary: Humphries et al. 2005 demonstrated TOMM40 localization to the outer
      membrane by subcellular fractionation and protease protection assays. Core CC.
    action: ACCEPT
- term:
    id: GO:0005741
    label: mitochondrial outer membrane
  evidence_type: EXP
  original_reference_id: PMID:31206022
  review:
    summary: Namba 2019 confirmed TOMM40 at OM via immunofluorescence and co-IP.
      Redundant with PMID:15644312 evidence for same term.
    action: ACCEPT
- term:
    id: GO:0030150
    label: protein import into mitochondrial matrix
  evidence_type: IMP
  original_reference_id: PMID:15644312
  review:
    summary: Humphries et al. showed depletion of TOMM40 compromises protein import.
      However, this is expected for the general import channel. Non-core because
      TOMM40 serves all import routes, not specifically matrix import.
    action: KEEP_AS_NON_CORE
- term:
    id: GO:0005741
    label: mitochondrial outer membrane
  evidence_type: NAS
  original_reference_id: PMID:18331822
  review:
    summary: Kato & Mihara 2008 identified Tom5 and Tom6 in the human TOM complex
      and confirmed Tom40 as an outer membrane component. Redundant with EXP evidence.
    action: ACCEPT
- term:
    id: GO:0045040
    label: protein insertion into mitochondrial outer membrane
  evidence_type: NAS
  original_reference_id: PMID:18331822
  review:
    summary: This term refers to insertion of proteins INTO the outer membrane (e.g.,
      alpha-helical or beta-barrel proteins). TOMM40 itself is inserted into the OM
      but does not catalyze insertion of others — that is the role of SAM (for beta-barrels)
      and MTCH2/MIM (for alpha-helical proteins). TOMM40 facilitates translocation
      THROUGH the outer membrane, not insertion into it.
    action: MODIFY
    reason: TOMM40 is a translocation channel, not an insertase. It translocates
      proteins across the OM, not into the OM lipid bilayer.
    proposed_replacement_terms:
    - id: GO:0008320
      label: protein transmembrane transporter activity
- term:
    id: GO:0140596
    label: TOM complex
  evidence_type: NAS
  original_reference_id: PMID:18331822
  review:
    summary: Kato & Mihara confirmed TOMM40 in the human TOM complex via immuno-isolation.
      GO:0140596 (TOM complex) is a more specific CC term than GO:0005742
      (mitochondrial outer membrane translocase complex). Both are correct.
    action: ACCEPT
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HTP
  original_reference_id: PMID:34800366
  review:
    summary: High-throughput mitochondrial proteome confirms TOMM40 as mitochondrial.
      Too general — more specific OM annotation exists.
    action: MARK_AS_OVER_ANNOTATED
    reason: Subsumed by mitochondrial outer membrane annotation.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31206022
  review:
    summary: Namba 2019 showed TOMM40 interacts with BCAP31 at ER-mitochondria contact
      sites. Protein binding is uninformative per guidelines.
    action: REMOVE
    reason: Protein binding is uninformative. The BCAP31 interaction is a non-core
      MAM function.
- term:
    id: GO:0044233
    label: mitochondria-associated endoplasmic reticulum membrane contact site
  evidence_type: IDA
  original_reference_id: PMID:31206022
  review:
    summary: Namba 2019 demonstrated TOMM40 localizes to MAM via interaction with
      BCAP31. This is a secondary localization beyond its primary OM residence.
      The MAM function (facilitating Complex I assembly) is a non-core role.
    action: KEEP_AS_NON_CORE
    reason: MAM localization is secondary to the core TOM complex function.
- term:
    id: GO:0070585
    label: protein localization to mitochondrion
  evidence_type: IGI
  original_reference_id: PMID:31206022
  review:
    summary: Namba 2019 showed BAP31-TOMM40 complex mediates NDUFS4 translocation
      to mitochondria. This is a specific aspect of TOMM40 general import function.
      The term is quite general but captures TOMM40 role in protein localization.
    action: KEEP_AS_NON_CORE
    reason: General term; the specific Complex I assembly role via BAP31 is non-core.
- term:
    id: GO:0005743
    label: mitochondrial inner membrane
  evidence_type: IDA
  original_reference_id: PMID:24746669
  review:
    summary: PMID:24746669 is about Cyclin B1/Cdk1 and mitochondrial respiration.
      TOMM40 is an outer membrane beta-barrel protein. Inner membrane localization
      is incorrect — TOMM40 may contact the IM via supercomplex formation with TIM
      complexes, but it is not an IM resident protein.
    action: REMOVE
    reason: TOMM40 is an outer membrane protein. Inner membrane annotation is
      incorrect; likely an artifact of co-fractionation.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:27554484
  review:
    summary: Kang et al. 2016 showed TIMM29 interacts with TOMM40, linking TIM22
      to TOM complex. Protein binding is uninformative per guidelines.
    action: REMOVE
    reason: Protein binding is uninformative. The TIM22-TOM interaction via TIMM29
      is better captured by TOM complex CC annotation.
- term:
    id: GO:0005741
    label: mitochondrial outer membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-5205661
  review:
    summary: Reactome pathway for PINK1 recruitment to mitochondria. Confirms TOMM40
      at the outer membrane. Redundant with direct experimental evidence.
    action: ACCEPT
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IDA
  original_reference_id: PMID:15644312
  review:
    summary: Extremely generic CC term. TOMM40 is specifically in the mitochondrial
      outer membrane (GO:0005741), which is already well-annotated.
    action: MARK_AS_OVER_ANNOTATED
    reason: Too general; subsumed by mitochondrial outer membrane.
- term:
    id: GO:0008320
    label: protein transmembrane transporter activity
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: Ortholog-based transfer of transporter activity. Correct and redundant
      with IBA evidence for same term.
    action: ACCEPT
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IMP
  original_reference_id: PMID:11745481
  negated: true
  review:
    summary: PMID:11745481 (Das et al. 2001) identified TOMM40 as p38.5/Haymaker and
      reported differential expression in malignant cells. The NOT annotation for
      mitochondrion localization is incorrect — TOMM40 is definitively a mitochondrial
      protein. This may reflect early confusion about the gene identity.
    action: REMOVE
    reason: The NOT|mitochondrion annotation contradicts overwhelming evidence that
      TOMM40 is a core mitochondrial outer membrane protein.
- term:
    id: GO:0005741
    label: mitochondrial outer membrane
  evidence_type: ISS
  original_reference_id: PMID:10980201
  review:
    summary: Based on rat Tom40 characterization (Suzuki et al. 2000). Correct —
      outer membrane localization is conserved.
    action: ACCEPT
- term:
    id: GO:0005742
    label: mitochondrial outer membrane translocase complex
  evidence_type: IDA
  original_reference_id: PMID:12198123
  review:
    summary: Johnston et al. 2002 identified TOMM40 in the ~380 kDa TOM complex
      by BN-PAGE and supershift analysis. Direct experimental evidence for TOM
      complex membership.
    action: ACCEPT
- term:
    id: GO:0005742
    label: mitochondrial outer membrane translocase complex
  evidence_type: IDA
  original_reference_id: PMID:15644312
  review:
    summary: Humphries et al. 2005 confirmed TOMM40 in TOM complex by BN-PAGE.
      Redundant with PMID:12198123 but independent confirmation.
    action: ACCEPT
- term:
    id: GO:0008320
    label: protein transmembrane transporter activity
  evidence_type: TAS
  original_reference_id: PMID:15644312
  review:
    summary: Humphries et al. described TOMM40 as the channel-forming subunit
      essential for protein import. Core MF annotation.
    action: ACCEPT
core_functions:
- molecular_function:
    id: GO:0008320
    label: protein transmembrane transporter activity
  description: >-
    TOMM40 is the central beta-barrel channel of the TOM complex, the main entry
    gate for nuclear-encoded mitochondrial precursor proteins. Two copies of TOMM40
    form a dimeric pore in the outer membrane through which virtually all imported
    proteins pass, regardless of their final destination (matrix, inner membrane,
    IMS, or outer membrane). The channel interacts with mitochondrial targeting
    sequences during translocation.
  directly_involved_in:
  - id: GO:0030150
    label: protein import into mitochondrial matrix
  - id: GO:0045041
    label: protein import into mitochondrial intermembrane space
  locations:
  - id: GO:0005741
    label: mitochondrial outer membrane
  in_complex:
    id: GO:0005742
    label: mitochondrial outer membrane translocase complex
  supported_by:
  - reference_id: PMID:15644312
    supporting_text: >-
      Tom40 is the channel-forming subunit of the translocase of the mitochondrial
      outer membrane (TOM complex), essential for protein import into mitochondria.
  - reference_id: PMID:12198123
    supporting_text: >-
      We found that the 120-kDa complex contains Tom40 and lacks receptor
      components. This intermediate can be chased to the stable approximately
      380-kDa mammalian TOM complex that additionally contains Tom22.
  - reference_id: file:human/TOMM40/TOMM40-deep-research-falcon.md
    supporting_text: >-
      **Primary molecular function:** Tom40 (TOMM40 product) is a **β‑barrel
      translocation pore** in the mitochondrial outer membrane that enables
      **import of nuclear-encoded mitochondrial precursor proteins** into
      mitochondria as part of the TOM complex.
references:
- id: file:human/TOMM40/TOMM40-deep-research-falcon.md
  title: Falcon deep research report for TOMM40
  findings:
  - statement: >-
      Falcon corroborates TOMM40 as the beta-barrel TOM complex pore in the
      mitochondrial outer membrane and separates this core import function from
      less direct APOE-region disease association signals.
    supporting_text: >-
      **Primary molecular function:** Tom40 (TOMM40 product) is a **β‑barrel
      translocation pore** in the mitochondrial outer membrane that enables
      **import of nuclear-encoded mitochondrial precursor proteins** into
      mitochondria as part of the TOM complex.
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
    by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: PMID:10980201
  title: Characterization of rat TOM40, a central component of the preprotein translocase
    of the mitochondrial outer membrane.
  findings:
  - statement: >-
      Mammalian Tom40 is embedded in the mitochondrial outer membrane likely as a
      beta-barrel, lacking predicted alpha-helical transmembrane segments.
    supporting_text: >-
      Although it has no predictable alpha-helical transmembrane segments, OM38
      is resistant to alkaline carbonate extraction and is inaccessible to
      proteases and polyclonal antibodies added from outside the mitochondria,
      suggesting that it is embedded in the membrane, probably in a beta-barrel
      structure
    reference_section_type: ABSTRACT
  - statement: >-
      Tom40 is a component of an ~400-kDa TOM complex, firmly associating with
      Tom22 and with the import receptor Tom20.
    supporting_text: >-
      Blue native polyacrylamide gel electrophoresis revealed that OM38 is a
      component of a approximately 400-kDa complex, firmly associating with
      rTOM22 and loosely associating with rTOM20.
    reference_section_type: ABSTRACT
  - statement: >-
      Tom40 is essential for preprotein import activity of the mitochondrial
      outer membrane.
    supporting_text: >-
      The preprotein in transit to the matrix interacted with the TOM complex
      containing OM38, and immunodepletion of OM38 resulted in the loss of
      preprotein import activity of the detergent-solubilized and reconstituted
      outer membrane vesicles.
    reference_section_type: ABSTRACT
- id: PMID:11745481
  title: Genetic identity and differential expression of p38.5 (Haymaker) in human
    malignant and nonmalignant cells.
  findings:
  - statement: >-
      Identifies the p38.5 (Haymaker) protein as the chromosome-19 gene product
      later recognized as TOMM40, with elevated expression in malignant cells.
    supporting_text: >-
      Sequence analyses of these cDNA clones reveal open reading frames (ORFs)
      that include the previously identified 11-mer peptide from purified,
      native p38.5 and that have identical sequences to a gene of unknown
      function on chromosome 19.
    reference_section_type: ABSTRACT
- id: PMID:12198123
  title: Insertion and assembly of human tom7 into the preprotein translocase complex
    of the outer mitochondrial membrane.
  findings:
  - statement: >-
      In human mitochondria, newly imported Tom7 assembles into a ~120-kDa
      Tom40-containing intermediate that is chased into the mature ~380-kDa TOM
      complex upon addition of Tom22.
    supporting_text: >-
      We found that the 120-kDa complex contains Tom40 and lacks receptor
      components. This intermediate can be chased to the stable approximately
      380-kDa mammalian TOM complex that additionally contains Tom22.
    reference_section_type: ABSTRACT
  - statement: >-
      Tom40 is the channel-forming core of the general import pore complex that
      translocates preproteins into mitochondria.
    supporting_text: >-
      Tom7 is a component of the translocase of the outer mitochondrial membrane
      (TOM) and assembles into a general import pore complex that translocates
      preproteins into mitochondria.
    reference_section_type: ABSTRACT
- id: PMID:15644312
  title: Dissection of the mitochondrial import and assembly pathway for human Tom40.
  findings:
  - statement: >-
      TOMM40 is the channel-forming subunit of the human TOM complex and is
      essential for protein import into mitochondria.
    supporting_text: >-
      Tom40 is the channel-forming subunit of the translocase of the
      mitochondrial outer membrane (TOM complex), essential for protein import
      into mitochondria.
    reference_section_type: ABSTRACT
  - statement: >-
      Hsp90 chaperones delivery of the Tom40 precursor to mitochondria in an
      ATP-dependent manner before its assembly via the TOM and SAM complexes.
    supporting_text: >-
      We identify that Hsp90 is involved in delivery of the Tom40 precursor to
      mitochondria in an ATP-dependent manner. The precursor then forms its
      first stable intermediate with the outer face of the TOM complex before
      its membrane integration and assembly.
    reference_section_type: ABSTRACT
  - statement: >-
      Efficient assembly of human Tom40 into the mature TOM complex requires
      the outer membrane SAM complex (Sam50).
    supporting_text: >-
      we show that Tom40 assembly is reduced in mitochondria depleted of human
      Sam50.
    reference_section_type: ABSTRACT
- id: PMID:18331822
  title: Identification of Tom5 and Tom6 in the preprotein translocase complex of
    human mitochondrial outer membrane.
  findings:
  - statement: >-
      Human Tom40 is the central import channel of the TOM complex and small
      Tom5/Tom6/Tom7 subunits maintain the structural integrity of the complex.
    supporting_text: >-
      The fungal preprotein translocase of the mitochondrial outer membrane
      (TOM complex) comprises import receptors Tom70, Tom20, and Tom22, import
      channel Tom40, and small Tom proteins Tom5, Tom6, and Tom7
    reference_section_type: ABSTRACT
  - statement: >-
      Depletion of TOMM40 in human cells reduces the steady-state levels of all
      small Tom subunits, indicating Tom40 is required for their stability in
      the TOM complex.
    supporting_text: >-
      Conversely, knockdown of hTom40 decreased the level of all small Tom
      proteins.
    reference_section_type: ABSTRACT
- id: PMID:24746669
  title: Cyclin B1/Cdk1 coordinates mitochondrial respiration for cell-cycle G2/M
    progression.
  findings:
  - statement: >-
      Cited in the context of mitochondrial respiration regulation; the study
      shows cyclin B1/Cdk1 phosphorylates mitochondrial complex I subunits in
      the matrix (not a direct TOMM40 function paper).
    supporting_text: >-
      a fraction of cyclin B1/Cdk1 proteins localizes to the matrix of
      mitochondria and phosphorylates a cluster of mitochondrial proteins,
      including the complex I (CI) subunits in the respiratory chain.
    reference_section_type: ABSTRACT
- id: PMID:27554484
  title: Tim29 is a novel subunit of the human TIM22 translocase and is involved in
    complex assembly and stability.
  findings:
  - statement: >-
      TOMM40 physically interacts with Tim29 to couple the outer-membrane TOM
      complex to the inner-membrane TIM22 carrier translocase in human
      mitochondria.
    supporting_text: >-
      Furthermore, Tim29 contacts the Translocase of the Outer Mitochondrial
      Membrane, TOM complex, enabling a mechanism for transport of hydrophobic
      carrier substrates across the aqueous intermembrane space.
    reference_section_type: ABSTRACT
  - statement: >-
      Chemical cross-linking and co-immunoprecipitation demonstrate a direct
      hTom40-Tim29 interaction that bridges the TIM22 and TOM complexes.
    supporting_text: >-
      we found hTom40 cross-linked to Tim29... these results suggest that Tim29
      acts as a bridge between the TIM22 and TOM complexes.
    reference_section_type: RESULTS
- id: PMID:31206022
  title: BAP31 regulates mitochondrial function via interaction with Tom40 within
    ER-mitochondria contact sites.
  findings:
  - statement: >-
      TOMM40 interacts with the ER membrane protein BAP31 at ER-mitochondria
      contact sites to facilitate import of the complex I subunit NDUFS4.
    supporting_text: >-
      BAP31 interacts with mitochondria-localized proteins, including Tom40, to
      stimulate the translocation of NDUFS4, the component of complex I from
      the cytosol to the mitochondria.
    reference_section_type: ABSTRACT
  - statement: >-
      Disruption of the BAP31-Tom40 bridging complex impairs mitochondrial
      complex I activity and oxygen consumption due to reduced NDUFS4 import.
    supporting_text: >-
      Disruption of the BAP31-Tom40 complex inhibits mitochondrial complex I
      activity and oxygen consumption by the decreased NDUFS4 localization to
      the mitochondria.
    reference_section_type: ABSTRACT
- id: PMID:31412244
  title: TOM40 Targets Atg2 to Mitochondria-Associated ER Membranes for Phagophore
    Expansion.
  findings:
  - statement: >-
      TOMM40 directly binds the autophagy lipid-transfer protein Atg2A via its
      C-terminal MAM localization domain, recruiting Atg2A to mitochondria-
      associated ER membranes during phagophore expansion.
    supporting_text: >-
      Proteomic analysis identifies the outer mitochondrial membrane protein
      TOM40 as a MLD-interacting partner. The Atg2A-TOM40 interaction is
      responsible for MAM localization of Atg2A and requires the TOM receptor
      protein TOM70.
    reference_section_type: ABSTRACT
  - statement: >-
      The TOM70-TOM40 complex recruits Atg2A to the MAM to enable lipid
      transfer for autophagosome expansion.
    supporting_text: >-
      we propose a model that the TOM70-TOM40 complex recruits Atg2A to the MAM
      for vesicular and/or non-vesicular lipid transport into the expanding
      phagophore to grow the size of autophagosomes for efficient autophagic
      flux.
    reference_section_type: ABSTRACT
- id: PMID:34800366
  title: Quantitative high-confidence human mitochondrial proteome and its dynamics
    in cellular context.
  findings:
  - statement: >-
      TOMM40 is included in the high-confidence human mitochondrial proteome
      (MitoCoP), confirming its mitochondrial localization as a translocase
      subunit.
    supporting_text: >-
      We classified >8,000 proteins in mitochondrial preparations of human
      cells and defined a mitochondrial high-confidence proteome of >1,100
      proteins (MitoCoP). We identified interactors of translocases, respiratory
      chain, and ATP synthase assembly factors.
    reference_section_type: ABSTRACT
- id: Reactome:R-HSA-5205661
  title: Pink1 is recruited from the cytoplasm to the mitochondria
  findings: []

TOMM40

Gene Description

Existing Annotations Review

Core Functions

References

Deep Research

Falcon

Research Report: Human TOMM40 (UniProt O96008) — Functional Annotation, Mechanism, and Disease-Linked Evidence (2023–2024 prioritized)

1. Target verification (identity, organism, family/domain alignment)

2. Key concepts and definitions (current understanding)

2.1 TOM complex and mitochondrial protein import

2.2 TOMM40/Tom40 molecular function

2.3 Receptor–pore coupling: Tom20/Tom22/Tom70

3. Subcellular localization and complex membership

3.1 Localization

3.2 Core subunits and structural organization

4. Recent developments (prioritizing 2023–2024)

4.1 High-resolution structural insights into human TOM/Tom40 (2024)

4.2 Structural plasticity and receptor positioning (Tom20) in the human TOM holo complex (Su et al., 2024)

4.3 Mechanistic open questions and emerging models (2024)

5. Pathways, interaction partners, and functional context

5.1 TOM–TIM coupling and downstream import routes

5.2 Quality control at the TOM pore (import stress, clogging, UPS)

6. Current applications and real-world implementations

6.1 Structural biology as a platform for mechanistic inference

6.2 TOMM40 genetic variation used in clinical-trial stratification (TOMMORROW)

7. Expert opinions and authoritative analyses (selected 2024 sources)

7.1 TOM complex as a dynamic, mechanistically unresolved but structurally tractable gateway

7.2 TOMM40 within the APOE locus: interpretation cautions

8. Disease associations: Alzheimer’s disease locus evidence (2023–2024 prioritized)

8.1 Autopsy-based neuropathology GWAS suggests limited TOMM40-independent signal after APOE adjustment (2024)

8.2 Proteome-wide association implicates TOMM40 as part of an AD dementia risk network (2024)

8.3 APOE-genotype-stratified epigenetics highlights TOMM40 CpG differences but not clear expression mediation (2024)

8.4 Linkage disequilibrium (LD) patterns constrain “independence” claims for TOMM40 polymorphisms

9. Relevant statistics and data highlights (from retrieved studies)

10. Summary table of evidence (2023–2024 focus)

11. Practical functional annotation (concise)

Citations

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