MIM complex

GO:0140595 · Other · Multiprotein complex · Proposed

A protein complex located in the mitochondrial outer membrane that functions as an insertase, mediating the insertion of alpha-helical proteins from the cytosol into the outer membrane. Client proteins are usually single- and multi-span proteins that include components of the TOM complex. [GO:0140595]

MIM deletion and heterologous rescue phenotypes in W303-derived Saccharomyces cerevisiae, not an image of the MIM complex itself. Full Figure 5: mito-GFP fluorescence and bright-field images of wild type, mim1 deletion, mim2 deletion and double-deletion cells carrying empty vector or trypanosomal pATOM36 (A; scale bars 5 micrometers), with tubular versus fragmented mitochondrial morphology quantified across three experiments (B). pATOM36 expression restores tubular morphology; it is a functional substitute, not a MIM constituent. Original multipanel figure retained. FLUORESCENCE · *Saccharomyces cerevisiae* (`NCBITaxon:4932`) · Daniela G Vitali, Sandro Käser, Antonia Kolb, Kai S Dimmer, Andre Schneider, Doron Rapaport; CC BY, via PubMed Central · CC_BY_4_0 · source: PMC PMC6010339.1 fig5 · `DOI:10.7554/eLife.34488`

Synonyms: mitochondrial outer import machinery

Part of: mitochondrial outer membrane (GO:0005741)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
Outer membrane protein, MIM1/TOM13, mitochondrial	Protein	part of	`InterPro:IPR013262`	MIM1, TOM13			Mim1 subunit of the mitochondrial outer-membrane alpha-helical protein import complex. `DOI:10.1016/j.celrep.2020.107567` Mim1 and Mim2 co-purify with imported Msp1 and Fis1; mim1-23 disrupts MIM-dependent import while preserving TOM and SAM complexes. `DOI:10.7554/eLife.34488` Both Mim1 and Mim2 are needed for effective heterologous rescue of ATOM-complex assembly. This does not establish fixed native subunit copy numbers. `InterPro:IPR013262` Verified MIM1/TOM13 family; the historical TOM13 name does not make Mim1 a constitutive TOM subunit.
Mim2	Protein	part of	`InterPro:IPR037652`	MIM2			Partner subunit of Mim1 in the mitochondrial outer-membrane import complex. `DOI:10.1016/j.celrep.2020.107567` Mim2 accompanies Mim1 in substrate-associated complexes purified after precursor import. `DOI:10.7554/eLife.34488` Coexpressed Mim1 and Mim2 form a native-like complex in trypanosomes; expression dominated by either subunit alone does not rescue ATOM assembly. Heterologous complementation is not natural taxonomic occurrence. `InterPro:IPR037652` Verified Mim2 family, distinct from the Mim1/TOM13 family.

Taxonomic distribution

NCBITaxon:4932 Saccharomyces cerevisiae — COMMON: Experimentally characterized in budding-yeast YPH499 derivatives; no universal fungal or eukaryotic distribution is asserted. [DOI:10.1016/j.celrep.2020.107567]

Canonical examples

NCBITaxon:4932 Saccharomyces cerevisiae — YPH499-derived strains provide isolated-mitochondrial import, affinity-purification and native-gel evidence. The separate 2018 deletion/rescue microscopy uses W303 derivatives. Heterologous expression in Trypanosoma brucei is not evidence for a native trypanosome MIM complex. [DOI:10.1016/j.celrep.2020.107567]

Functions

alpha helical protein insertion into mitochondrial outer membrane GO:7770059 — Promotes biogenesis of selected signal-anchored, tail-anchored and multispanning alpha-helical mitochondrial outer-membrane proteins; dependence varies with substrate and assay.
- DOI:10.1016/j.celrep.2020.107567 Radiolabeled precursor import, mim1-23 controls and precursor co-purification support an import role. Fis1 and Gem1 import are impaired under these isolated-mitochondrial assay conditions; these results do not prove an exclusive route.
- DOI:10.1016/j.isci.2019.100779 Msp1 import is strongly MIM dependent, Gem1 is only moderately dependent, and Fis1 and Mcr1 mitochondrial levels are largely MIM independent. This preserves the contrast with the later import assays.
- DOI:10.7554/eLife.34488 Loss of Mim1/Mim2 impairs Tom20 and Ugo1 import. Heterologous pATOM36 rescues Tom20 much more effectively than Ugo1, so functional interchangeability is substrate limited.

Mechanism graphs

MIM-dependent import and distinct TOM/SAM-associated populations (FUNCTION)

MIM promotes selected precursor-import and assembly reactions and associates separately with TOM and SAM.

Subject	Predicate	Object	Evidence
MIM complex	associates with	mitochondrial outer membrane translocase complex	`DOI:10.1016/j.celrep.2020.107567` Figure 3A: Tom20-His affinity purification and BN-PAGE recover a TOM-MIM population distinct from free MIM and SAM-associated MIM.
MIM complex	associates with	SAM complex	`DOI:10.1016/j.celrep.2020.107567` Figure 3A: Sam35-His affinity purification and BN-PAGE recover SAM-associated MIM. Apparent native-gel size does not determine stoichiometry.
MIM complex	promotes	Import of tested signal-anchored precursors	`DOI:10.1016/j.celrep.2020.107567` Figure 1: deletion and mim1-23 import assays plus substrate co-purification distinguish MIM involvement from secondary loss of TOM/SAM. The Mcr1 claim concerns the membrane form, not the soluble intermembrane-space isoform.
MIM complex	promotes	Import of tested tail-anchored precursors	`DOI:10.1016/j.celrep.2020.107567` Figure 2: import is impaired in mim1-deletion and mim1-23 mitochondria; imported His-Fis1 co-purifies Mim1 and Mim2. MIM assistance is not equivalent to absolute dependence.
MIM complex	promotes formation of	SAM-associated Tom6 assembly intermediate	`DOI:10.1016/j.celrep.2020.107567` Figure 4C-D: mim1 perturbations reduce the intermediate, Sam35-HA antibody shift identifies SAM association, and a Sam50 POTRA deletion enhances both MIM-SAM association and Tom6 intermediate formation. Direct molecular handoff is inferred rather than visualized.

Discussions

INTERPRETATION (RESOLVED): Distinguish MIM constituents from interacting import systems, substrates and functional substitutes. TOM and SAM association, precursor binding and heterologous rescue do not establish additional constitutive MIM components.
CONTROVERSY (OPEN): Resolve the assay-dependent differences in Fis1 and Mcr1 dependence on MIM. The iScience study finds largely preserved mitochondrial levels of Fis1 and Mcr1 and only minor Fis1 mistargeting, whereas the later Cell Reports import assays detect MIM-dependent effects. Steady-state abundance, targeting fidelity and import kinetics are different readouts; these sources do not establish which experimental differences explain the contrast.
CURATION_TODO (OPEN): Resolve native MIM stoichiometry and the proposed exchange between free, TOM-associated and SAM-associated populations. Native-gel migration and complementation do not resolve an intact atomic structure or fixed copy number. Competition and altered association support a dynamic-exchange model without directly observing exchange. The hosted microscopy shows organelle morphology, not molecular MIM localization or structure.

Evidence

DOI:10.1016/j.celrep.2020.107567 Doan et al. (2020), The Mitochondrial Import Complex MIM Functions as Main Translocase for alpha-Helical Outer Membrane Proteins. Main text, Figures 1-4 and experimental methods inspected in the institutional publisher PDF. CC BY-NC-ND: figures not hosted.
DOI:10.7554/eLife.34488 Independent evolution of functionally exchangeable mitochondrial outer membrane import complexes. Relevant yeast and heterologous Results, Discussion, strain/microscopy methods and Figure 5 inspected in checksum-verified PMC6010339 version 1.
DOI:10.1016/j.isci.2019.100779 The Biogenesis of Mitochondrial Outer Membrane Proteins Show Variable Dependence on Import Factors. Signal-anchored and tail-anchored Results, Discussion and limitations inspected in checksum-verified PMC6965732 version 1.
GO:0098799 Broader is-a parent: outer mitochondrial membrane protein complex.
GO:0005741 Containing mitochondrial outer membrane, not an is-a parent.

Curation history

2026-10-04T23:11:03Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-04T23:13:24Z codex · EXPANDED_RECORD — Added verified Mim1/Mim2 families, yeast-bounded examples, exact GO insertion function, five source-cited functional edges and explicit substrate-dependence, partner-boundary and architecture limits.
2026-10-04T23:14:29Z pmc_oa · ADD_IMAGE — Added PMC6010339.1 fig5; version, CC licence, JATS figure identity and media md5 verified through the PMC OA S3 dataset.

Source: data/structures/other/mim_complex.yaml