ATAD3B

ATAD3B is a primate-specific mitochondrial AAA-ATPase that hetero-oligomerizes with ATAD3A and negatively regulates ATAD3A's interaction with mitochondrial matrix nucleoid complexes, contributing to mitochondrial fragmentation and mtDNA organization (PMID:22664726). Under basal conditions, the ATAD3B C-terminus is sequestered in the intermembrane space through ATAD3A binding, but oxidative stress or mtDNA damage disrupts this hetero-oligomer, exposing a LIR motif at the outer mitochondrial membrane that directly recruits LC3 to drive PINK1-independent mitophagy and selective clearance of damaged mtDNA (PMID:33665835). Knockdown of ATAD3B causes polynucleation, decreased proliferation, and increased apoptosis, indicating a required role in cell division (PMID:16909202). Deletions generating chimeric ATAD3B/ATAD3A fusion genes cause a fatal neurological disorder with mtDNA abnormalities and altered cholesterol metabolism (PMID:28549128).

1. 2006 Medium

   The initial characterization of ATAD3B established it as a mitochondrial AAA-ATPase with two isoforms required for normal cell division, resolving whether this gene encodes a functional protein or a pseudogene.

   Evidence siRNA knockdown in human cells with RT-PCR, Western blot, confocal imaging, and cell-cycle analysis

   PMID:16909202

   Open questions at the time

   • Mechanism linking mitochondrial ATAD3B to polynucleation unknown
   • ATPase activity not directly demonstrated
   • Relationship to the paralog ATAD3A not defined
2. 2012 Medium

   ATAD3B was shown to hetero-oligomerize with ATAD3A and negatively regulate ATAD3A's association with nucleoid complexes, establishing the first functional relationship between the two paralogs and linking ATAD3B to mtDNA organization and mitochondrial morphology.

   Evidence Co-IP, gain- and loss-of-function experiments, mitochondrial morphology assays in human cells

   PMID:22664726

   Open questions at the time

   • Stoichiometry and structural basis of the ATAD3A–ATAD3B oligomer unresolved
   • Direct contact sites with nucleoid proteins not mapped
   • Regulatory signals controlling hetero-oligomerization unknown
3. 2017 Medium

   Patient genetics demonstrated that disruption of the ATAD3 gene cluster (generating ATAD3B/ATAD3A chimeric fusions) causes a fatal neurological disorder with mtDNA abnormalities and altered cholesterol metabolism, establishing disease relevance and a dual role in mtDNA maintenance and lipid homeostasis.

   Evidence SNP array, WES, mtDNA analysis, and cholesterol assays in fibroblasts from four unrelated families

   PMID:28549128

   Open questions at the time

   • Contribution of ATAD3B loss versus gain of a chimeric protein not disentangled
   • Mechanism linking ATAD3 proteins to cholesterol metabolism not defined
4. 2021 High

   The key mechanistic advance was demonstrating that ATAD3B acts as a mitophagy receptor: oxidative stress disrupts ATAD3A–ATAD3B hetero-oligomerization, exposing a C-terminal LIR motif on the outer mitochondrial membrane that directly binds LC3 to drive PINK1-independent mitophagy and selective clearance of damaged mtDNA.

   Evidence Reciprocal Co-IP, LIR motif mutagenesis, LC3 binding assays, subcellular fractionation, mitophagy flux assays under oxidative stress, mtDNA depletion experiments

   PMID:33665835

   Open questions at the time

   • Structural basis for how ATAD3A masks the ATAD3B LIR motif unresolved
   • Whether ATAD3B also functions in non-stress mitophagy not tested
   • In vivo validation in animal models lacking ATAD3B not possible due to primate specificity
5. 2026 Medium

   SEC62 at mitochondria-associated membranes was identified as a direct ATAD3B interactor that downregulates ATAD3B, linking impaired ATAD3B-dependent mitophagy to mitochondrial ROS accumulation and inflammatory responses in metabolic disease (MASH).

   Evidence Co-IP, SEC62 overexpression/knockout in hepatocytes, mitophagy assays, ROS measurement

   PMID:42001994

   Open questions at the time

   • Mechanism by which SEC62 reduces ATAD3B expression (transcriptional vs. post-translational) not defined
   • Whether SEC62 disrupts ATAD3A–ATAD3B hetero-oligomerization specifically not tested
   • In vivo relevance in human MASH liver tissue not confirmed

• The structural basis of ATAD3A–ATAD3B hetero-oligomerization, the mechanism by which oligomer disassembly exposes the LIR motif, and the ATPase-dependent versus ATPase-independent functions of ATAD3B remain unresolved.
• No crystal or cryo-EM structure of the ATAD3A–ATAD3B complex
• ATPase activity of ATAD3B not directly measured
• Selectivity mechanism for damaged versus healthy mtDNA nucleoids not defined