TIMM29

TIMM29 is a metazoan-specific subunit of the human TIM22 carrier translocase in the mitochondrial inner membrane, where it underpins the import of hydrophobic multi-spanning carrier proteins from the cytosol (PMID:27554484, PMID:27718247). Integrated into the inner membrane with its C-terminus exposed to the intermembrane space, TIMM29 is required for the structural stability of the ~440 kDa TIM22 complex, facilitates assembly of the hTim22 channel, and physically bridges the TIM22 complex to the TOM complex to enable transport of substrates across the aqueous intermembrane space (PMID:27554484, PMID:27718247). It assembles with TIMM22 and AGK as a core constituent of the complex, with AGK contributing independently of its kinase activity (PMID:28712724). Through this import activity, TIMM29 supports delivery of iron transporters to mitochondria; its loss reduces mitochondrial iron uptake and disrupts iron-sulfur cluster biogenesis, a defect rescued by reconstituting mitochondrial iron levels in cells and in zebrafish (PMID:41418755). A biallelic loss-of-function variant (p.Trp172Arg) causes a severe form of Sengers syndrome marked by combined respiratory chain complex deficiency and reduced ANT1 levels (PMID:40022150). Independently of its translocase role, TIMM29 binds the preS1 region of the hepatitis B virus large S protein and restricts HBV replication, acting partly through upregulation of the host factors SRSF1 and ARRDC3 (PMID:32970362, PMID:38294104, PMID:39956808).

1. 2016 High

   Established that an uncharacterized inner-membrane protein (C19orf52) is a bona fide subunit of the carrier translocase, answering how the metazoan TIM22 complex is organized and connected to the import machinery.

   Evidence Reciprocal co-IP, subcellular fractionation, localization, and knockdown import assays in human cells; replicated by blue-native PAGE and siRNA import assays in a parallel study

   PMID:27554484 PMID:27718247

   Open questions at the time

   • No high-resolution structure of TIM29 within the assembled complex
   • Molecular details of the TIM22-TOM bridging contact not defined
2. 2017 High

   Defined the broader subunit composition of the TIM22 complex by showing AGK co-assembles with TIMM22 and TIMM29, clarifying that import function is structural rather than catalytic.

   Evidence Mitochondrial interactome MS, co-IP, import assays, and kinase-dead complementation in human cells

   PMID:28712724

   Open questions at the time

   • Stoichiometry of TIMM29 relative to AGK and TIMM22 not resolved
   • Direct interaction surface between TIMM29 and AGK not mapped
3. 2020 Medium

   Revealed a non-import function by showing TIMM29 directly binds HBV preS1 and restricts viral replication, raising the question of host antiviral roles for a mitochondrial translocase subunit.

   Evidence preS1 peptide IP, GST-pulldown, immunofluorescence co-localization, and HBV replication readouts in TIMM29 OE and KO cell lines

   PMID:32970362

   Open questions at the time

   • Single lab, no reciprocal validation in other models
   • Mechanism linking preS1 binding to replication restriction not established at this stage
4. 2024 Medium

   Began to define the downstream pathway of HBV restriction by linking TIMM29 overexpression to reduced core promoter activity via SRSF1 induction.

   Evidence TIM22/TIM29 overexpression in hepatocyte lines with HBV replication assays, core promoter reporters, and SRSF1 expression analysis

   PMID:38294104

   Open questions at the time

   • No KO confirmation that SRSF1 is required
   • Single lab; connection between mitochondrial role and SRSF1 induction unclear
5. 2025 Medium

   Mapped the TIMM29 domain and a second effector required for HBV restriction, showing the aa 99-192 region drives ARRDC3 upregulation to suppress viral transcription.

   Evidence Domain deletion mutants reconstituted into KO cells with gene expression microarrays and HBV replication assays

   PMID:39956808

   Open questions at the time

   • ARRDC3 sufficiency and necessity not directly tested by epistasis
   • Cell-type variability of BASP1 effect unexplained
   • Single lab
6. 2025 High

   Connected TIMM29 import activity to organismal physiology by showing its loss impairs mitochondrial iron uptake and Fe-S cluster biogenesis, with iron reconstitution rescuing the defect.

   Evidence CRISPR KO and co-essentiality analysis, Fe-S biogenesis assays, iron reconstitution rescue, and zebrafish timm29 knockdown rescue

   PMID:41418755

   Open questions at the time

   • Identity of the specific iron transporters dependent on TIM22 import not fully enumerated
   • Whether the iron defect fully accounts for proliferation phenotypes
7. 2025 Medium

   Established TIMM29 as a disease gene by linking a biallelic loss-of-function variant to a severe form of Sengers syndrome with combined respiratory chain deficiency and reduced ANT1.

   Evidence Homozygosity mapping, sequencing, patient tissue biochemistry, and Drosophila orthologue RNAi knockdown

   PMID:40022150

   Open questions at the time

   • Single family/study
   • Genotype-phenotype correlation across other variants not established
   • Mechanistic basis of ANT1 reduction not directly demonstrated

• How TIMM29 reconciles its core carrier-import function with its distinct HBV-restriction activity, and whether the two operate through the same molecular surface, remains unresolved.
• No structural model of TIM29 in the assembled TIM22 complex
• Unclear whether HBV restriction depends on translocase activity or is independent
• Full substrate repertoire of the TIM22 complex incompletely defined