ALDH16A1

ALDH16A1 is a pseudoenzyme member of the aldehyde dehydrogenase superfamily that has lost catalytic aldehyde oxidation activity due to the absence of the conserved catalytic cysteine, as confirmed by crystal structure determination, SAXS, and in vitro enzymatic assays (PMID:30529746). It retains the three-domain ALDH fold and forms a unique homodimer that mimics the classic ALDH dimer-of-dimers architecture (PMID:30529746). ALDH16A1 is expressed in kidney proximal and distal tubule cells and zone 3 hepatocytes; knockout mice exhibit dysregulated urate transporter expression and altered lipid metabolism, indicating a non-enzymatic regulatory role in renal homeostasis (PMID:28254523). ALDH16A1 directly binds thioredoxin (TXN), occluding its active site and promoting its lysosomal degradation, thereby sensitizing cells to ferroptosis within a SMARCA4–ALDH16A1–TXN regulatory axis (PMID:40897711).

1. 2009 Medium

   Identifying ALDH16A1's first physical interaction partner established that this uncharacterized ALDH family member participates in protein–protein interactions, specifically with the spastic paraplegia gene product maspardin/ACP33.

   Evidence Co-immunoprecipitation with mass spectrometry, reciprocal pull-down, and colocalization of overexpressed proteins in mammalian cells

   PMID:19184135

   Open questions at the time

   • Functional consequence of the ALDH16A1–maspardin interaction is unknown
   • Endogenous interaction not validated
   • No structural detail on the binding interface
2. 2013 Low

   Computational analysis predicted that mammalian ALDH16A1 is a non-catalytic pseudoenzyme (lacking the essential Cys-302) and proposed an interaction with the purine salvage enzyme HPRT1 that could link ALDH16A1 to uric acid metabolism.

   Evidence Molecular modeling, sequence alignment across species, and structural prediction of HPRT1 binding

   PMID:23348497

   Open questions at the time

   • HPRT1 interaction was computationally predicted only and has not been experimentally validated
   • Pseudoenzyme status was inferred from sequence alone without biochemical confirmation
   • Gout-associated variant effect on interaction remains unconfirmed experimentally
3. 2017 Medium

   Generation of Aldh16a1 knockout mice revealed that loss of ALDH16A1 dysregulates urate transporters and lipid metabolism in the kidney, establishing an in vivo non-enzymatic regulatory function and defining its tissue expression pattern.

   Evidence Gene-targeted knockout mouse with RNA-seq, plasma metabolomics, and immunohistochemistry

   PMID:28254523

   Open questions at the time

   • Molecular mechanism by which ALDH16A1 influences urate transporter expression is unknown
   • Direct binding partners mediating the renal phenotype were not identified
   • Single-lab study without independent replication
4. 2018 High

   Crystal structures of bacterial ALDH16 and SAXS analysis of human ALDH16A1 definitively confirmed the pseudoenzyme status and revealed a unique three-domain fold with a C-terminal Rossmann-like domain that creates a novel dimeric architecture mimicking the classic ALDH tetramer.

   Evidence High-resolution X-ray crystallography of Loktanella ALDH16 (four structures), in vitro aldehyde oxidation and esterase assays, SAXS on recombinant human ALDH16A1

   PMID:30529746

   Open questions at the time

   • No high-resolution crystal structure of human ALDH16A1 itself
   • Whether the NAD+-binding site in human ALDH16A1 retains any ligand-binding function is untested
   • Structural basis for any protein–protein interaction is unresolved
5. 2025 High

   Discovery that ALDH16A1 directly binds TXN, occludes its active site, and promotes its lysosomal degradation provided the first complete molecular mechanism for the pseudoenzyme, placing it in a SMARCA4–ALDH16A1–TXN axis that governs ferroptosis susceptibility in cancer cells.

   Evidence ATAC-seq, co-immunoprecipitation, TXN enzymatic activity assays, lysosomal translocation/degradation assays, SMARCA4 KO/rescue, and in vivo tumor models in NSCLC

   PMID:40897711

   Open questions at the time

   • Structural basis of ALDH16A1–TXN binding and active-site occlusion has not been resolved at atomic resolution
   • Whether the SMARCA4–ALDH16A1–TXN axis operates in non-cancerous tissues (e.g., kidney) is unknown
   • Relationship between the TXN-regulatory function and the previously observed maspardin interaction is unexplored

• Key unresolved questions include the atomic-resolution structure of human ALDH16A1 in complex with TXN, whether the predicted HPRT1 interaction exists and connects to the renal urate phenotype, and how ALDH16A1's pseudoenzyme scaffold integrates maspardin binding with TXN regulation.
• No high-resolution structure of human ALDH16A1 alone or in complex with any partner
• HPRT1 interaction never experimentally validated
• Functional integration of maspardin and TXN interactions is completely unexplored