ALDH16A1

ALDH16A1 is a catalytically inactive member of the aldehyde dehydrogenase superfamily that operates as a pseudoenzyme scaffold, exerting its biological effects through protein-protein interactions rather than enzymatic catalysis (PMID:30529746, PMID:40897711). Although the bacterial ortholog ALDH16 is a bona fide NAD+-dependent enzyme, human ALDH16A1 lacks the essential catalytic cysteine and shows no measurable aldehyde oxidation activity while retaining the conserved ALDH dimer fold (PMID:30529746). Functionally, ALDH16A1 binds directly to thioredoxin (TXN), occluding its active site to inhibit its oxidoreductase activity and facilitating TXN translocation to the lysosome for degradation; this axis lies downstream of SMARCA4, which opens chromatin at the ALDH16A1 locus to drive its expression and thereby sensitizes non-small-cell lung cancer cells to ferroptosis (PMID:40897711). ALDH16A1 also physically interacts with the SPG21 protein maspardin/ACP33 and colocalizes with it in cells (PMID:19184135), and in mouse it localizes to renal proximal and distal tubule cells and zone-3 hepatocytes, where its loss dysregulates urate transporter expression and plasma lipid profiles, implicating it in uric acid homeostasis (PMID:28254523).

1. 2009 Medium

   Before any function was assigned, the first direct binding partner of ALDH16A1 was identified, establishing it as an interaction partner of the spastic paraplegia protein maspardin.

   Evidence Co-immunoprecipitation with mass spectrometry, orthogonal pull-down, and immunofluorescence colocalization

   PMID:19184135

   Open questions at the time

   • Functional consequence of the maspardin interaction not defined
   • Interaction interface and stoichiometry unmapped
   • Work from a single lab without independent replication
2. 2013 Low

   Sequence analysis raised the possibility that human ALDH16A1 is enzymatically dead and computationally linked it to purine metabolism, framing it as a non-catalytic interactor relevant to gout.

   Evidence Bioinformatic sequence analysis and molecular modeling/docking of the HPRT1 interaction and the gout-associated ALDH16A1*2 variant

   PMID:23348497

   Open questions at the time

   • HPRT1 interaction is computational only, with no in vitro or cellular confirmation
   • Catalytic inactivity inferred from sequence, not yet demonstrated biochemically
   • Functional effect of the ALDH16A1*2 variant not tested experimentally
3. 2017 Medium

   A knockout mouse converted in silico inference into in vivo physiology, defining where ALDH16A1 is expressed and tying it to renal urate handling.

   Evidence Aldh16a1 knockout mouse with RNA-seq, plasma metabolomics, and immunohistochemistry showing urate transporter dysregulation and altered lipid profiles

   PMID:28254523

   Open questions at the time

   • Molecular mechanism linking ALDH16A1 to transporter expression unknown
   • No demonstrated direct interaction with urate transporters or purine enzymes
   • Single-lab phenotype not replicated
4. 2018 High

   Structural and biochemical work established definitively that human ALDH16A1 is a pseudoenzyme by comparing it to a catalytically competent bacterial ortholog.

   Evidence Crystal structures of bacterial ALDH16 with enzyme assays, plus SAXS and in vitro activity assays on recombinant human ALDH16A1

   PMID:30529746

   Open questions at the time

   • High-resolution atomic structure of human ALDH16A1 not solved
   • Non-catalytic functional surfaces for partner binding not mapped
   • Physiological consequence of pseudoenzyme status not addressed in this study
5. 2019 Low

   Crystallographic effort on the catalytically active frog homolog was undertaken to provide a structural counterpoint to the inactive human protein.

   Evidence Recombinant Xenopus tropicalis ALDH16B1 expressed, purified, and crystallized with diffraction data to 2.5 Å

   PMID:30894314

   Open questions at the time

   • Structure not solved at time of publication; finding is preliminary
   • No comparison of active-site architecture to human ALDH16A1 yet available
6. 2025 High

   A defined molecular function was finally established: ALDH16A1 acts as a TXN-inhibiting, TXN-degrading scaffold within a SMARCA4-driven ferroptosis pathway in cancer.

   Evidence Reciprocal Co-IP, TXN oxidoreductase activity assay, lysosomal fractionation, ATAC-seq, and SMARCA4 loss-of-function with ferroptosis assays in NSCLC cells

   PMID:40897711

   Open questions at the time

   • Structural basis of TXN active-site occlusion not resolved
   • Mechanism of ALDH16A1-mediated lysosomal targeting of TXN undefined
   • Relationship between the TXN/ferroptosis role and the renal/urate role unexplored

• How the distinct ALDH16A1 activities — maspardin binding, renal urate regulation, and TXN-mediated ferroptosis control — are integrated into a single mechanistic framework remains unresolved.
• No unifying model connecting the trans-Golgi/endosomal maspardin interaction to the lysosomal TXN-degradation function
• Predicted HPRT1 interaction still lacks experimental confirmation
• No high-resolution structure of human ALDH16A1 bound to any partner