dph2

UniProt ID: A4QN59
Organism: Danio rerio
Review Status: COMPLETE
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Gene Description

Dph2 is a subunit of the Dph1-Dph2 heterodimeric complex that catalyzes the first step of diphthamide biosynthesis, the transfer of a 3-amino-3-carboxypropyl (ACP) group from S-adenosyl-L-methionine to a conserved histidine of eukaryotic translation elongation factor 2 (eEF2). Dph2 binds a [4Fe-4S] cluster that facilitates reduction of the catalytic iron-sulfur cluster in the Dph1 subunit. Diphthamide is a unique post-translational modification of eEF2 that ensures translational fidelity and is the target of diphtheria toxin ADP-ribosylation. Loss of DPH2 function in humans causes diphthamide-deficiency syndrome, an autosomal recessive developmental disorder.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0017183 protein histidyl modification to diphthamide
IBA
GO_REF:0000033
ACCEPT
Summary: Phylogenetic inference from orthologs in yeast (DPH1, DPH2) and mouse correctly places dph2 in the diphthamide biosynthesis pathway. The DPH1-DPH2 heterodimer catalyzes the first step of diphthamide synthesis on eEF2, a pathway conserved from archaea to vertebrates.
Supporting Evidence:
PMID:32576952
The gene products DPH1 and DPH2 are components of a heterodimeric enzyme complex that mediates the first step of the posttranslational diphthamide modification on the nonredundant eukaryotic translation elongation factor 2 (eEF2)
file:DANRE/dph2/dph2-deep-research-falcon.md
DPH2 (together with DPH1) functions in the ...first committed step... of diphthamide biosynthesis: transfer of a ...3-amino-3-carboxypropyl (ACP)... group derived from ...S-adenosylmethionine (SAM/AdoMet)... onto the ...C2 of the imidazole ring... of a conserved eEF2 histidine. This ACP addition generates an early diphthamide-pathway intermediate on eEF2
GO:0017183 protein histidyl modification to diphthamide
IEA
GO_REF:0000120
ACCEPT
Summary: Combined automated annotation from InterPro domain matches (IPR010014, IPR016435) and UniPathway correctly assigns diphthamide biosynthesis. Consistent with the well-characterized biochemical role of DPH2 family proteins.
Supporting Evidence:
PMID:20559380
Diphthamide biosynthesis requires an organic radical generated by an iron-sulphur enzyme
GO:0090560 2-(3-amino-3-carboxypropyl)histidine synthase activity
IEA
GO_REF:0000002
MARK AS OVER ANNOTATED
Summary: InterPro2GO mapping from IPR016435 (Diphthamide synthesis DPH1/DPH2 family) assigns the ACP synthase activity with an implicit enables qualifier. However, Dph2 does not independently catalyze the reaction; the radical chemistry resides in the Dph1 subunit. The ISS annotation (below) correctly uses contributes_to. This IEA annotation over-annotates by implying Dph2 independently enables the activity.
Reason: The IEA annotation assigns the full enables qualifier, but Dph2 only contributes to the complex activity. The ISS annotation with contributes_to qualifier is the correct representation.
Supporting Evidence:
PMID:20559380
Diphthamide biosynthesis requires an organic radical generated by an iron-sulphur enzyme
PMID:24422557
Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent to the homodimer of PhDph2 and is sufficient to catalyze the first step in vitro in the presence of dithionite as the reductant
GO:0120513 2-(3-amino-3-carboxypropyl)histidine synthase complex
ISS
GO_REF:0000024
ACCEPT
Summary: Sequence similarity transfer from yeast DPH2 (P32461). Dph2 is a subunit of the Dph1-Dph2 heterodimer in eukaryotes, which together with Dph3 and NADH-dependent reductase forms the ACP synthase complex. Well supported by biochemical evidence in yeast and archaea.
Supporting Evidence:
PMID:24422557
Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent to the homodimer of PhDph2 and is sufficient to catalyze the first step in vitro
file:DANRE/dph2/dph2-deep-research-falcon.md
Modern pathway summaries indicate the initial step is catalyzed by an Fe–S DPH1/DPH2 heterodimer, with involvement of DPH3/DPH4 in supporting the reaction
GO:0017183 protein histidyl modification to diphthamide
ISS
GO_REF:0000024
ACCEPT
Summary: Sequence similarity transfer from yeast DPH2 (P32461). This duplicates the IBA and IEA annotations for the same term but with ISS evidence. The annotation is correct as DPH2 is required for diphthamide biosynthesis.
Supporting Evidence:
PMID:32576952
The gene products DPH1 and DPH2 are components of a heterodimeric enzyme complex that mediates the first step of the posttranslational diphthamide modification on the nonredundant eukaryotic translation elongation factor 2 (eEF2)
GO:0051539 4 iron, 4 sulfur cluster binding
ISS
GO_REF:0000024
ACCEPT
Summary: Sequence similarity transfer from yeast DPH2 (P32461). The zebrafish Dph2 has three conserved cysteine residues (Cys89, Cys110, Cys341) that coordinate a [4Fe-4S] cluster, as annotated in UniProt by similarity. The Dph2 cluster facilitates reduction of the catalytic cluster in Dph1 rather than directly participating in radical chemistry.
Supporting Evidence:
PMID:34154323
all radical S-adenosylmethionine (radical-SAM) enzymes, including the noncanonical radical-SAM enzyme diphthamide biosynthetic enzyme Dph1-Dph2, require at least one [4Fe-4S](Cys)3 cluster for activity
file:DANRE/dph2/dph2-deep-research-falcon.md
One Fe-S cluster per subunit; atypical cysteine motifs instead of canonical CX3CX2C radical-SAM motif
GO:0090560 2-(3-amino-3-carboxypropyl)histidine synthase activity
ISS
GO_REF:0000024
ACCEPT
Summary: Sequence similarity transfer from yeast DPH2 (P32461) with the correct contributes_to qualifier. Dph2 is required for ACP synthase activity as part of the Dph1-Dph2 complex but does not independently catalyze the radical SAM reaction. The contributes_to qualifier appropriately reflects that Dph1 houses the catalytic [4Fe-4S] cluster.
Supporting Evidence:
PMID:29590073
Diphthamide biosynthesis involves a carbon-carbon bond-forming reaction catalyzed by a radical S-adenosylmethionine (SAM) enzyme that cleaves a carbon-sulfur (C-S) bond in SAM to generate a 3-amino-3-carboxypropyl (ACP) radical
PMID:24422557
Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent to the homodimer of PhDph2 and is sufficient to catalyze the first step in vitro in the presence of dithionite as the reductant
file:DANRE/dph2/dph2-deep-research-falcon.md
Dph1 and Dph2 are homologous and are thought to form a ...heterodimer... that is functionally analogous to archaeal homodimeric Dph2
GO:0005737 cytoplasm
ISS NEW
Summary: Dph2 functions in the cytoplasm where it forms a complex with Dph1 to modify cytoplasmic eEF2. The diphthamide biosynthesis machinery operates on eEF2 in the cytosol, consistent with its role in translation elongation. No transmembrane domains or signal peptides are present.
Reason: Cytoplasmic localization is implied by the function of the Dph1-Dph2 complex on cytosolic eEF2 but was not explicitly annotated in GOA. The BioReason SFT analysis also identified cytoplasmic localization.
Supporting Evidence:
file:DANRE/dph2/dph2-deep-research-bioreason-sft.md
The cellular component is dictated by where eEF2 resides and where ferredoxin-coupled redox partners operate. The adaptor must access cytosolic eEF2 and the cytosolic ferredoxin/reductase chain, supporting localization to the GO:0005737 cytoplasm
file:DANRE/dph2/dph2-deep-research-falcon.md
diphthamide is a modification on the ...cytosolic translation factor eEF2..., so the pathway is expected to act in the ...cytosol... ...Arabidopsis DPH2 localizes to the cytosol and physically interacts with DPH1..., consistent with a cytosolic biosynthetic complex acting on cytosolic eEF2

Core Functions

Subunit of the Dph1-Dph2 heterodimer that catalyzes transfer of a 3-amino-3-carboxypropyl group from SAM to a conserved histidine of eEF2, the first committed step in diphthamide biosynthesis. Dph2 binds a [4Fe-4S] cluster that facilitates reduction of the catalytic cluster in Dph1, while Dph1 performs the radical SAM chemistry. The resulting diphthamide modification ensures translational reading frame fidelity.

Supporting Evidence:
  • PMID:24422557
    Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent to the homodimer of PhDph2 and is sufficient to catalyze the first step in vitro in the presence of dithionite as the reductant
  • PMID:29590073
    Diphthamide biosynthesis involves a carbon-carbon bond-forming reaction catalyzed by a radical S-adenosylmethionine (SAM) enzyme that cleaves a carbon-sulfur (C-S) bond in SAM to generate a 3-amino-3-carboxypropyl (ACP) radical
  • PMID:34154323
    all radical S-adenosylmethionine (radical-SAM) enzymes, including the noncanonical radical-SAM enzyme diphthamide biosynthetic enzyme Dph1-Dph2, require at least one [4Fe-4S](Cys)3 cluster for activity
  • file:DANRE/dph2/dph2-deep-research-falcon.md
    Mature diphthamide on eEF2 supports translational fidelity and suppresses spurious -1 frameshifting

References

Gene Ontology annotation through association of InterPro records with GO terms
Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
Annotation inferences using phylogenetic trees
Combined Automated Annotation using Multiple IEA Methods
Diphthamide biosynthesis requires an organic radical generated by an iron-sulphur enzyme
  • The Dph2 enzyme in Pyrococcus horikoshii uses a [4Fe-4S] cluster to generate an organic radical from SAM for diphthamide biosynthesis
    "Diphthamide biosynthesis requires an organic radical generated by an iron-sulphur enzyme"
Organometallic and radical intermediates reveal mechanism of diphthamide biosynthesis
  • The diphthamide biosynthetic enzyme generates an organometallic intermediate with an iron-carbon bond between ACP and the [4Fe-4S] cluster, followed by a product-like radical on eEF2
    "Diphthamide biosynthesis involves a carbon-carbon bond-forming reaction catalyzed by a radical S-adenosylmethionine (SAM) enzyme that cleaves a carbon-sulfur (C-S) bond in SAM to generate a 3-amino-3-carboxypropyl (ACP) radical"
Dph3 is an electron donor for Dph1-Dph2 in the first step of eukaryotic diphthamide biosynthesis
  • Dph3 (KTI11) serves as the physiological electron donor to reduce the [4Fe-4S] cluster in the Dph1-Dph2 complex
    "Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent to the homodimer of PhDph2 and is sufficient to catalyze the first step in vitro in the presence of dithionite as the reductant"
Dph3 enables aerobic diphthamide biosynthesis by donating one iron atom to transform a [3Fe-4S] to a [4Fe-4S] cluster in Dph1-Dph2
  • Dph3 donates an iron atom to restore a functional [4Fe-4S] cluster in the Dph1-Dph2 complex under aerobic conditions
    "all radical S-adenosylmethionine (radical-SAM) enzymes, including the noncanonical radical-SAM enzyme diphthamide biosynthetic enzyme Dph1-Dph2, require at least one [4Fe-4S](Cys)3 cluster for activity"
Diphthamide-deficiency syndrome -- a novel human developmental disorder and ribosomopathy
  • Biallelic DPH2 mutations cause diphthamide-deficiency syndrome with intellectual disability, seizures, and developmental abnormalities
    "The gene products DPH1 and DPH2 are components of a heterodimeric enzyme complex that mediates the first step of the posttranslational diphthamide modification on the nonredundant eukaryotic translation elongation factor 2 (eEF2)"
DPH1 and DPH2 variants that confer susceptibility to diphthamide deficiency syndrome in human cells and yeast models
  • DPH2 variants H105P and C341Y abolish diphthamide biosynthesis, confirmed in human cells and yeast functional assays
    "Ten additional human DPH1...and two DPH2 (H105P, C341Y) variants showed reduced functionality and hence are deficiency-susceptibility alleles"
Diphthamide deficiency promotes association of eEF2 with p53 to induce p21 expression and neural crest defects
  • Diphthamide deficiency causes eEF2 to dissociate from ribosomes and associate with p53, driving p21-mediated growth arrest and neural crest defects
    "DPH1 depletion facilitates dissociation of eEF2 from ribosomes and association with p53 to promote transcription of the cell cycle inhibitor p21, resulting in inhibited proliferation"
Diphthamide -- a conserved modification of eEF2 with clinical relevance
  • Comprehensive review of diphthamide as a conserved eEF2 modification affecting translational fidelity, viral susceptibility, and human disease
    "Diphthamide, a complex modification on eukaryotic translation elongation factor 2 (eEF2), assures reading-frame fidelity during translation"
file:DANRE/dph2/dph2-deep-research-bioreason-sft.md
BioReason SFT reasoning trace for dph2 (Danio rerio)
  • BioReason SFT identifies dph2 as a nucleocytoplasmic adaptor for diphthamide biosynthesis that organizes the Dph1-Dph2-Dph3 complex
file:DANRE/dph2/dph2-deep-research-falcon.md
Falcon deep research for zebrafish dph2 (Danio rerio, A4QN59)
  • No zebrafish-specific primary studies naming UniProt A4QN59 or zgc:162269 were retrieved; functional assignments are based on highly conserved, mechanistically characterized eukaryotic/archaeal DPH2 homologs given the strong conservation of the diphthamide biosynthesis pathway from archaea to humans.
    "I did ...not... find zebrafish-specific primary studies explicitly naming UniProt A4QN59 or zgc:162269; therefore, organism-specific phenotypes or expression patterns for zebrafish are not asserted here. Functional statements are based on ...highly conserved, mechanistically characterized eukaryotic/archaeal DPH2 homologs..."
  • Dph2, with Dph1, catalyzes the first committed step of diphthamide biosynthesis - transfer of the 3-amino-3-carboxypropyl (ACP) group from SAM onto the imidazole C2 of a conserved eEF2 histidine.
    "DPH2 (together with DPH1) functions in the ...first committed step... of diphthamide biosynthesis: transfer of a ...3-amino-3-carboxypropyl (ACP)... group derived from ...S-adenosylmethionine (SAM/AdoMet)... onto the ...C2 of the imidazole ring... of a conserved eEF2 histidine"
  • The Dph1-Dph2 catalytic module is a non-canonical radical-SAM enzyme that uses Fe-S clusters but does not employ the canonical CX3CX2C motif and generates an ACP radical rather than the classical 5'-deoxyadenosyl radical.
    "it uses Fe–S clusters but does ...not... rely on the canonical ...CX3CX2C... motif and does ...not... generate the classical 5′-deoxyadenosyl radical; instead it generates an ...ACP radical... from SAM cleavage that is then used to functionalize eEF2 histidine"
  • Diphthamide on eEF2 supports translational fidelity and suppresses spurious -1 frameshifting; in mammalian cells its loss perturbs RRM1 translation and elevates DNA replication stress.
    "Mature diphthamide on eEF2 supports translational fidelity and suppresses spurious -1 frameshifting; deficiency perturbs translation of proteins such as RRM1 and elevates DNA replication stress"
  • Dph2 acts in the cytosol on cytosolic eEF2; experimental cytosolic localization of Arabidopsis DPH2 (interacting with DPH1) supports this expectation for the conserved complex.
    "Arabidopsis DPH2 localizes to the cytosol and physically interacts with DPH1..., consistent with a cytosolic biosynthetic complex acting on cytosolic eEF2"

Suggested Questions for Experts

Q: Is there direct experimental evidence for dph2 function in zebrafish, or are all functional assignments based on orthology to yeast and human DPH2?

Q: Does zebrafish dph2 deficiency produce neural crest or craniofacial phenotypes analogous to those seen in mouse Dph1 knockin models?

Q: Is the [4Fe-4S] cluster in zebrafish dph2 essential for its function, and does Dph3-mediated iron donation operate similarly in fish?

Suggested Experiments

Experiment: CRISPR-Cas9 knockout of dph2 in zebrafish embryos to assess developmental phenotypes, particularly craniofacial and neural crest derivatives, with comparison to dph1 mutants

Experiment: In vitro reconstitution of zebrafish Dph1-Dph2 complex to confirm ACP transferase activity and [4Fe-4S] cluster requirements using site-directed mutagenesis of the three conserved cysteine residues

Deep Research

Bioreason Pro

(dph2-deep-research-bioreason-sft.md)
Thinking Trace Bioreason Pro SFT

Thinking Trace

I begin with the InterPro architecture. Three overlapping family signaturesIPR016435 (Diphthamide synthesis DPH1/DPH2 family, residues 2490), IPR010014 (Diphthamide synthesis DHP2 family, residues 20485), and IPR016435 (DPH1/DPH2 family, residues 29484)span essentially the full polypeptide, indicating a conserved, non-enzymatic adaptor specialized for the diphthamide pathway. Within this scaffold, two homologous-superfamily modules are resolved: IPR042263 (DPH1/DPH2, domain 1, residues 35126) and IPR042265 (DPH1/DPH2, domain 3, residues 264366). Additional family-level matches (IPR016435 [54377]) reinforce that the central body of the protein is devoted to this adaptor role rather than catalysis. The absence of catalytic domain signatures and the dominance of DPH1/DPH2-family scaffolding motifs argue that this proteins primary molecular function is to bind other proteins and organize a redox-coupled transfer reaction rather than to perform the chemistry itself.

This domain layout causes a specific molecular function: it creates a multivalent platform that binds the radical-SAM enzyme DPH1 and the electron-delivery component DPH3, and positions the histidine target on eEF2. Such scaffolding necessarily entails GO:0005515 protein binding as a core activity. The DPH1/DPH2 adaptor stabilizes the DPH1 active site, aligns the [4Fe–4S]-dependent radical generation with the eEF2 histidine, and couples electron flow from NADH via cytosolic ferredoxin and ferredoxin reductase to the DPH1 radical chemistry. Because the adaptor does not house the catalytic iron–sulfur cluster or the radical chemistry, its contribution is to protein–protein recognition and spatial organization of the electron-transfer chain.

From this molecular function, the biological process follows. By enabling the first step of diphthamide formation on eEF2—removal of the 3-amino-3-deoxy ribose on His1a and creation of a 3-(3-amino-3-carboxypropyl)histidine—the adaptor initiates a post-translational modification that tunes translation elongation fidelity and modulates susceptibility to ADP-ribosylating toxins. This places the protein in the diphthamide biosynthetic process (inferred as GO:0017183). In vertebrates, proper eEF2 modification influences tissue morphogenesis and extracellular matrix production; perturbation of this pathway can manifest as defects in skeletal and cartilage development, which rationalizes involvement in GO:0051216 cartilage development.

The cellular component is dictated by where eEF2 resides and where ferredoxin-coupled redox partners operate. The adaptor must access cytosolic eEF2 and the cytosolic ferredoxin/reductase chain, supporting localization to the GO:0005737 cytoplasm. A nuclear pool is also plausible because eEF2 shuttles and certain assembly or quality-control steps can occur near chromatin-associated translation factors; the scaffold’s solubility and lack of transmembrane features are consistent with a nucleocytoplasmic distribution, including the GO:0005634 nucleus.

Mechanistically, the adaptor forms a ternary complex with DPH1 and DPH3, recruits reduced ferredoxin generated by ferredoxin reductase (NADH-dependent), and docks eEF2 so that DPH1’s radical chemistry can proceed on His1a. Downstream enzymes—DPH5, DPH6, DPH7, and the amidoligase (Dph8/DnaJ family in some systems)—complete the maturation to diphthamide. The listed partners align with this model: DPH3 (electron carrier), DPH5/DPH6/DPH7 (later pathway enzymes), and diphthine–ammonia ligase (Dph8) for the final ligation/processing steps. Multiple eEF2 paralogs (eukaryotic translation elongation factor 2 and its like/tandem-duplicate variants) are the direct substrates that the adaptor presents to the radical machinery. A DnaJ/Hsp40 homolog likely assists folding or assembly of the complex, stabilizing the iron–sulfur enzyme and its scaffold during electron transfer cycles. Together, this architecture and partner set produce a controlled, redox-driven modification of eEF2 that impacts translational fidelity and, secondarily, developmental programs such as cartilage formation.

## Functional Summary

A nucleocytoplasmic adaptor that organizes the first step of the diphthamide modification on the histidine of translation elongation factor 2. It binds the radical-generating enzyme and the ferredoxin-based electron-delivery system, aligns eEF2 for precise chemistry, and thereby enables formation of the aminoaldehyde side chain on the target histidine. By ensuring efficient eEF2 modification, it supports accurate translation and influences developmental programs, including cartilage formation.

## UniProt Summary

Required for the first step of diphthamide biosynthesis, a post-translational modification of histidine which occurs in elongation factor 2. DPH1 and DPH2 together assist the reaction catalyzed by DPH1, which transfers a 3-amino-3-deoxy sugar from eEF2 to an active site histidine residue, forming a 3-(3-amino-3-carboxypropyl)histidine residue. DPH1 is a radical-SAM protein and its catalytic cycle is dependent on electron transfer from NADH via FDXR (ferredoxin reductase) and FDX1 (ferredoxin). DPH2 is not a radical-SAM protein but is required for the reaction and probably acts by binding to DPH1 and eEF2 to facilitate the reaction (By similarity).

## InterPro Domains

    - IPR016435: Diphthamide synthesis DPH1/DPH2 (family) [2-490]
- IPR010014: Diphthamide synthesis DHP2 (family) [20-485]
- IPR016435: Diphthamide synthesis DPH1/DPH2 (family) [29-484]
- IPR016435: Diphthamide synthesis DPH1/DPH2 (family) [33-366]
- IPR042263: Diphthamide synthesis DPH1/DPH2, domain 1 (homologous_superfamily) [35-126]
- IPR016435: Diphthamide synthesis DPH1/DPH2 (family) [54-377]
- IPR042265: Diphthamide synthesis DPH1/DPH2, domain 3 (homologous_superfamily) [264-366]

## GO Term Predictions

### Molecular Function


### Biological Process


### Cellular Component

Falcon

(dph2-deep-research-falcon.md)
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 24 citations 1 artifacts 2026-05-30T11:51:28.769584

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research report: dph2 / DPH2 (Danio rerio; UniProt A4QN59) — functional annotation via conserved diphthamide biosynthesis biology

0) Target verification and scope control (critical)

The user-specified zebrafish protein DPH2 (UniProt A4QN59; gene dph2; ORFName zgc:162269) is annotated as “2-(3-amino-3-carboxypropyl)histidine synthase subunit 2 / diphthamide biosynthesis protein 2”, belonging to the DPH1/DPH2 family (DPH2 subfamily). Within the retrieved scientific corpus, I did not find zebrafish-specific primary studies explicitly naming UniProt A4QN59 or zgc:162269; therefore, organism-specific phenotypes or expression patterns for zebrafish are not asserted here. Functional statements are based on highly conserved, mechanistically characterized eukaryotic/archaeal DPH2 homologs, which is appropriate given the strong conservation of the diphthamide biosynthesis pathway from archaea to humans. (liu2004identificationofthe pages 1-2, su2013thebiosynthesisand pages 3-4)

1) Key concepts and definitions (current understanding)

1.1 Diphthamide (the modified residue)

Diphthamide is a post-translationally modified histidine that occurs exclusively on eukaryotic translation elongation factor 2 (eEF2) and is the molecular target of diphtheria toxin–family ADP-ribosylating toxins. Cells lacking diphthamide are toxin-resistant because the toxin substrate is absent. (liu2004identificationofthe pages 1-2, su2013thebiosynthesisand pages 3-4)

1.2 DPH2 as a core enzyme in diphthamide biosynthesis

DPH2 (together with DPH1) functions in the first committed step of diphthamide biosynthesis: transfer of a 3-amino-3-carboxypropyl (ACP) group derived from S-adenosylmethionine (SAM/AdoMet) onto the C2 of the imidazole ring of a conserved eEF2 histidine. This ACP addition generates an early diphthamide-pathway intermediate on eEF2. (liu2004identificationofthe pages 1-2, su2013thebiosynthesisand pages 3-4, utkur2023dph1anddph2 pages 1-2)

1.3 Pathway overview (DPH1–DPH7)

A foundational pathway outline (originally developed through yeast genetics and conserved across eukaryotes) is: (i) ACP transfer to eEF2 histidine; (ii) trimethylation to form diphthine; (iii) final amidation to yield mature diphthamide. (liu2004identificationofthe pages 1-2) More recent pathway summaries add defined roles for DPH6/DPH7 in the final maturation steps. (zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 1-2)

Pathway step Enzyme(s) / gene(s) Core reaction chemistry Key cofactors / partners Evidence type Selected supporting citation(s)
1. ACP transfer to eEF2 histidine (first committed step) DPH1-DPH4; catalytic core is DPH1•DPH2 Transfer of the 3-amino-3-carboxypropyl (ACP) group from SAM/AdoMet to the imidazole C2 of the target histidine on eEF2 (His715 in human; His699 in yeast), initiating diphthamide biosynthesis (liu2004identificationofthe pages 1-2, su2013thebiosynthesisand pages 3-4, utkur2023dph1anddph2 pages 1-2) DPH1•DPH2 heterodimer; DPH3 electron donation; DPH4 required in eukaryotes (su2013thebiosynthesisand pages 3-4, zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 1-2) Biochemical, review, genetics, cell biology Liu et al. 2004, Mol Cell Biol, 2004-11, https://doi.org/10.1128/mcb.24.21.9487-9497.2004; Su et al. 2013, Crit Rev Biochem Mol Biol, 2013-11, https://doi.org/10.3109/10409238.2013.831023; Ütkür et al. 2023, Dis Model Mech, 2023-09, https://doi.org/10.1242/dmm.050207 (liu2004identificationofthe pages 1-2, su2013thebiosynthesisand pages 3-4, utkur2023dph1anddph2 pages 1-2)
1a. Mechanistic detail of the DPH2-containing step DPH2 (archaeal homodimeric Dph2; eukaryotic DPH1•DPH2 analog) Non-canonical radical-SAM-like chemistry: cleavage of the Cγ,Met-S bond of SAM to generate MTA plus an ACP radical, rather than the classical 5'-deoxyadenosyl radical; the ACP radical then attacks eEF2 histidine (su2013thediscoveryand pages 16-21, su2013thebiosynthesisand pages 3-4, su2013thediscoveryand pages 108-116) One Fe-S cluster per subunit; atypical cysteine motifs instead of canonical CX3CX2C radical-SAM motif (utkur2024functionalintegrityof pages 1-2, su2013thebiosynthesisand pages 3-4, su2013thediscoveryand pages 108-116) Biochemical, review Su et al. 2013, Crit Rev Biochem Mol Biol, 2013-11, https://doi.org/10.3109/10409238.2013.831023 (su2013thebiosynthesisand pages 3-4); X. Su thesis summary 2013 (su2013thediscoveryand pages 16-21, su2013thediscoveryand pages 108-116)
1b. 2024 motif-level advance for DPH2 function DPH1•DPH2 Conserved tandem cysteine motifs adjacent to known Fe-S/SAM-binding cysteines are required for full activity and structural integrity; combined DPH2 cysteine substitutions nearly abolish activity and accelerate subunit decay (utkur2024functionalintegrityof pages 1-2, utkur2024functionalintegrityof pages 2-4) Non-canonical Fe-S/cofactor motifs in DPH1 and DPH2; dimer integrity depends on these residues (utkur2024functionalintegrityof pages 1-2, utkur2024functionalintegrityof pages 2-4) Biochemical, genetics Ütkür et al. 2024, Biomolecules, 2024-04, https://doi.org/10.3390/biom14040470 (utkur2024functionalintegrityof pages 1-2, utkur2024functionalintegrityof pages 2-4)
2. Trimethylation of ACP intermediate to diphthine DPH5 Methylation of the ACP-modified eEF2 intermediate to form diphthine (liu2004identificationofthe pages 1-2, zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 1-2) SAM/AdoMet methyl donor (liu2004identificationofthe pages 1-2, zhao2024lossofdiphthamide pages 1-2) Review, genetics, cell biology Liu et al. 2004, Mol Cell Biol, 2004-11, https://doi.org/10.1128/mcb.24.21.9487-9497.2004; Ütkür et al. 2023, Dis Model Mech, 2023-09, https://doi.org/10.1242/dmm.050207; Zhao et al. 2024, ACS Cent Sci, 2024-09, https://doi.org/10.1021/acscentsci.4c00967 (liu2004identificationofthe pages 1-2, utkur2023dph1anddph2 pages 1-2, zhao2024lossofdiphthamide pages 1-2)
3. Demethylation / preparation for amidation DPH7 Converts diphthine to the intermediate used for final amidation; described as a demethylation/preparatory step in recent pathway summaries (zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 1-2) Functions in downstream maturation of modified eEF2 (zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 1-2) Genetics, cell biology Ütkür et al. 2023, Dis Model Mech, 2023-09, https://doi.org/10.1242/dmm.050207; Zhao et al. 2024, ACS Cent Sci, 2024-09, https://doi.org/10.1021/acscentsci.4c00967 (utkur2023dph1anddph2 pages 1-2, zhao2024lossofdiphthamide pages 1-2)
4. Final amidation to diphthamide DPH6 ATP-dependent amidation of the carboxyl group to generate mature diphthamide on eEF2 (liu2004identificationofthe pages 1-2, zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 1-2) ATP-dependent amidation machinery (liu2004identificationofthe pages 1-2, zhao2024lossofdiphthamide pages 1-2) Biochemical, review, genetics Liu et al. 2004, Mol Cell Biol, 2004-11, https://doi.org/10.1128/mcb.24.21.9487-9497.2004; Ütkür et al. 2023, Dis Model Mech, 2023-09, https://doi.org/10.1242/dmm.050207; Zhao et al. 2024, ACS Cent Sci, 2024-09, https://doi.org/10.1021/acscentsci.4c00967 (liu2004identificationofthe pages 1-2, utkur2023dph1anddph2 pages 1-2, zhao2024lossofdiphthamide pages 1-2)
Biological consequence of complete pathway DPH1-DPH7 pathway acting on eEF2 Mature diphthamide on eEF2 supports translational fidelity and suppresses spurious -1 frameshifting; deficiency perturbs translation of proteins such as RRM1 and elevates DNA replication stress (zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 9-10) eEF2 as modified substrate; pathway defects linked to developmental disease and toxin resistance (utkur2023dph1anddph2 pages 9-10, utkur2024functionalintegrityof pages 1-2) Cell biology, genetics Zhao et al. 2024, ACS Cent Sci, 2024-09, https://doi.org/10.1021/acscentsci.4c00967; Ütkür et al. 2023, Dis Model Mech, 2023-09, https://doi.org/10.1242/dmm.050207; Ütkür et al. 2024, Biomolecules, 2024-04, https://doi.org/10.3390/biom14040470 (zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 9-10, utkur2024functionalintegrityof pages 1-2)

Table: This table summarizes the diphthamide biosynthesis pathway with emphasis on the DPH2-containing first step, the enzymes involved across DPH1-7, the reaction chemistry and cofactors, and key recent and foundational citations. It is useful as a compact reference for functional annotation of DPH2 and its pathway context.

2) Primary function of DPH2: reaction, substrate specificity, and mechanism

2.1 Chemical reaction catalyzed (first step)

The DPH2-containing enzyme system catalyzes ACP transfer from SAM to eEF2 histidine, initiating diphthamide formation. This is described explicitly as transfer of the 3-amino-3-carboxypropyl group of SAM/AdoMet to the imidazole C2 of the precursor histidine residue in eEF2. (liu2004identificationofthe pages 1-2, su2013thebiosynthesisand pages 3-4, utkur2023dph1anddph2 pages 1-2)

Substrates (core): SAM/AdoMet and eEF2 (target histidine). (liu2004identificationofthe pages 1-2, su2013thebiosynthesisand pages 3-4)

Key products/byproducts (mechanistic signatures): In archaeal Dph2 biochemistry, SAM cleavage yields 5′-deoxy-5′-methylthioadenosine (MTA) plus an ACP radical, rather than the 5′-deoxyadenosyl radical typical of canonical radical-SAM enzymes. (su2013thebiosynthesisand pages 3-4, su2013thediscoveryand pages 16-21)

2.2 Enzyme class and cofactors: noncanonical radical-SAM-like Fe–S chemistry

Mechanistic work (reviewing archaeal biochemistry and mapping to eukaryotes) supports that DPH2 functions as part of an iron–sulfur (Fe–S) enzyme system that generates an organic radical required for C–C bond formation in the ACP transfer reaction. (su2013thebiosynthesisand pages 10-14, su2013thebiosynthesisand pages 3-4)

A key modern framing is that the Dph1•Dph2 catalytic module constitutes a non-canonical radical SAM enzyme: it uses Fe–S clusters but does not rely on the canonical CX3CX2C motif and does not generate the classical 5′-deoxyadenosyl radical; instead it generates an ACP radical from SAM cleavage that is then used to functionalize eEF2 histidine. (su2013thebiosynthesisand pages 3-4, utkur2024functionalintegrityof pages 1-2)

2.3 Protein partners and complex architecture

In eukaryotes, DPH2 is functionally coupled to DPH1 (forming a heterodimeric core) and requires accessory proteins for efficient catalysis.

  • DPH1–DPH2 partnership: Dph1 and Dph2 are homologous and are thought to form a heterodimer that is functionally analogous to archaeal homodimeric Dph2. (su2013thebiosynthesisand pages 3-4)
  • DPH3 as electron donor: Dph3 can interact with the Dph1–Dph2 complex and is suggested to mediate electron transfer needed for catalysis. (su2013thebiosynthesisand pages 3-4)
  • DPH4 and additional machinery: Modern pathway summaries indicate the initial step is catalyzed by an Fe–S DPH1/DPH2 heterodimer, with involvement of DPH3/DPH4 in supporting the reaction. (utkur2023dph1anddph2 pages 1-2, zhao2024lossofdiphthamide pages 1-2)

3) Subcellular localization and where DPH2 acts

Direct localization evidence in zebrafish was not retrieved. However, diphthamide is a modification on the cytosolic translation factor eEF2, so the pathway is expected to act in the cytosol.

Experimental evidence from plants supports this expectation: Arabidopsis DPH2 localizes to the cytosol and physically interacts with DPH1, consistent with a cytosolic biosynthetic complex acting on cytosolic eEF2. (zhang2025diphthamideformationin pages 1-4)

4) Recent developments and latest research (prioritizing 2023–2024)

4.1 2024: Motif-level and cofactor-binding advances in DPH2-containing Dph1•Dph2

A 2024 study identified conserved tandem cysteine motifs (TCMs) adjacent to the noncanonical Fe–S binding motifs in Dph1 and Dph2, and showed these cysteines are required for full enzymatic activity and dimer stability. Combined substitution of adjacent cysteines in Dph2 (e.g., double substitution in the Dph2 TCM) nearly abolishes activity, and replacing key cysteine ligands accelerates degradation of both subunits—supporting a tight linkage between cofactor integrity and complex stability. (utkur2024functionalintegrityof pages 1-2, utkur2024functionalintegrityof pages 2-4)

These data refine current understanding of how DPH2 (within Dph1•Dph2) binds and maintains Fe–S cofactors in a noncanonical radical-SAM-like context. (utkur2024functionalintegrityof pages 1-2)

4.2 2023: Human DPH2 variant functionalization and disease susceptibility alleles

A 2023 Disease Models & Mechanisms paper functionally tested DPH1/DPH2 missense alleles and identified two human DPH2 variants (H105P, C341Y) with reduced function in diphthamide synthesis assays, supporting their classification as deficiency-susceptibility alleles. This provides contemporary genotype-to-biochemistry mapping and illustrates which conserved residues in DPH2 are particularly critical for activity. (utkur2023dph1anddph2 pages 1-2, utkur2023dph1anddph2 pages 4-5)

4.3 2024: New cellular roles—translation fidelity linked to replication stress via frameshifting

A 2024 ACS Central Science study connected diphthamide deficiency to DNA replication stress by showing that diphthamide modulates translation of RRM1 via −1 frameshifting, and that dysregulated RRM1 translation is causally linked to elevated replication stress in diphthamide-deficient mammalian cells. The paper emphasizes diphthamide’s role in restraining spurious frameshifting and maintaining translational fidelity, expanding the functional consequences of the DPH2-controlled pathway beyond toxin susceptibility. (zhao2024lossofdiphthamide pages 1-2)

5) Current applications and real-world implementations

5.1 Toxin biology and engineered toxins (conceptual/biomedical relevance)

Because diphthamide on eEF2 is the substrate for diphtheria toxin–like ADP-ribosylating toxins, DPH2 pathway status is directly relevant to toxin susceptibility/resistance at the cellular level. This principle underlies experimental systems in which loss of diphthamide biosynthesis confers resistance to toxins and can be used as a selection readout for pathway integrity. (liu2004identificationofthe pages 1-2, utkur2024functionalintegrityof pages 1-2)

5.2 Human genetics and diagnostic interpretation

Functional assays that quantify diphthamide synthesis (or toxin sensitivity) are used to interpret whether human DPH2 variants are likely pathogenic or hypomorphic, informing clinical genetics of diphthamide deficiency syndrome and related ribosomopathies. (utkur2023dph1anddph2 pages 1-2, utkur2023dph1anddph2 pages 4-5)

6) Expert opinions and authoritative synthesis (reviews and consensus framing)

A widely cited 2013 Critical Reviews in Biochemistry and Molecular Biology review frames DPH2 (via archaeal Dph2 biochemistry) as an unusual radical-SAM-type Fe–S enzyme that generates an ACP radical (rather than 5′-dAdo•) to drive the first step of diphthamide biosynthesis, and emphasizes outstanding mechanistic questions that continued to motivate subsequent structural and biochemical work. (su2013thebiosynthesisand pages 3-4, su2013thebiosynthesisand pages 10-14)

7) Relevant statistics and data (from recent studies)

  • Human variant counts with reduced function (2023): The 2023 study identified 2 DPH2 missense variants (H105P and C341Y) with strongly/significantly reduced diphthamide synthase activity in cell/yeast assays. (utkur2023dph1anddph2 pages 1-2, utkur2023dph1anddph2 pages 4-5)
  • Qualitative effect sizes (2024 motif study): Combined substitutions in Dph2 tandem cysteines “almost entirely” inactivate Dph1•Dph2 activity and accelerate subunit decay (qualitative, not a numeric metric in the retrieved excerpt). (utkur2024functionalintegrityof pages 2-4)
  • Replication-stress connection (2024): The 2024 ACS Central Science paper reports a mechanistic link between diphthamide loss, −1 frameshifting, altered RRM1 translation, and elevated replication stress, but numeric values (e.g., frameshift frequency changes or quantitative replication stress markers) are not present in the retrieved excerpt and would require deeper extraction from the full text. (zhao2024lossofdiphthamide pages 1-2)

8) Summary functional annotation for zebrafish dph2 (A4QN59)

Most supported primary molecular function (high-confidence by homology): zebrafish Dph2 is expected to be a Fe–S-dependent, noncanonical radical-SAM-like enzyme subunit that—together with Dph1—catalyzes the first committed step of diphthamide biosynthesis on eEF2: ACP transfer from SAM to the conserved eEF2 histidine. (liu2004identificationofthe pages 1-2, su2013thebiosynthesisand pages 3-4, utkur2024functionalintegrityof pages 1-2)

Likely cellular compartment: cytosol, consistent with cytosolic eEF2 as substrate and supported by experimental cytosolic localization of plant DPH2. (zhang2025diphthamideformationin pages 1-4)

Likely pathway membership: DPH1–DPH7 diphthamide biosynthesis pathway, supporting translational fidelity (frameshift suppression) and influencing downstream cellular stress phenotypes when perturbed. (zhao2024lossofdiphthamide pages 1-2, utkur2023dph1anddph2 pages 9-10)

Key cited sources (with publication dates and URLs)

  • Liu et al. “Identification of the proteins required for biosynthesis of diphthamide…” Molecular and Cellular Biology (Published 2004-11). https://doi.org/10.1128/mcb.24.21.9487-9497.2004 (liu2004identificationofthe pages 1-2)
  • Su et al. “The biosynthesis and biological function of diphthamide” Critical Reviews in Biochemistry and Molecular Biology (Published 2013-11). https://doi.org/10.3109/10409238.2013.831023 (su2013thebiosynthesisand pages 3-4, su2013thebiosynthesisand pages 10-14)
  • Ütkür et al. “DPH1 and DPH2 variants…” Disease Models & Mechanisms (Published 2023-09). https://doi.org/10.1242/dmm.050207 (utkur2023dph1anddph2 pages 1-2, utkur2023dph1anddph2 pages 4-5)
  • Ütkür et al. “Functional Integrity of Radical SAM Enzyme Dph1•Dph2…” Biomolecules (Published 2024-04). https://doi.org/10.3390/biom14040470 (utkur2024functionalintegrityof pages 1-2, utkur2024functionalintegrityof pages 2-4)
  • Zhao et al. “Loss of Diphthamide Increases DNA Replication Stress…” ACS Central Science (Published 2024-09). https://doi.org/10.1021/acscentsci.4c00967 (zhao2024lossofdiphthamide pages 1-2)

References

  1. (liu2004identificationofthe pages 1-2): Shihui Liu, G. Todd Milne, Jeffrey G. Kuremsky, Gerald R. Fink, and Stephen H. Leppla. Identification of the proteins required for biosynthesis of diphthamide, the target of bacterial adp-ribosylating toxins on translation elongation factor 2. Molecular and Cellular Biology, 24:9487-9497, Nov 2004. URL: https://doi.org/10.1128/mcb.24.21.9487-9497.2004, doi:10.1128/mcb.24.21.9487-9497.2004. This article has 204 citations and is from a domain leading peer-reviewed journal.

  2. (su2013thebiosynthesisand pages 3-4): Xiaoyang Su, Zhewang Lin, and Hening Lin. The biosynthesis and biological function of diphthamide. Critical Reviews in Biochemistry and Molecular Biology, 48:515-521, Nov 2013. URL: https://doi.org/10.3109/10409238.2013.831023, doi:10.3109/10409238.2013.831023. This article has 94 citations and is from a peer-reviewed journal.

  3. (utkur2023dph1anddph2 pages 1-2): Koray Ütkür, Klaus Mayer, Maliha Khan, Thirishika Manivannan, Raffael Schaffrath, and Ulrich Brinkmann. Dph1 and dph2 variants that confer susceptibility to diphthamide deficiency syndrome in human cells and yeast models. Disease Models & Mechanisms, Sep 2023. URL: https://doi.org/10.1242/dmm.050207, doi:10.1242/dmm.050207. This article has 9 citations and is from a domain leading peer-reviewed journal.

  4. (zhao2024lossofdiphthamide pages 1-2): Jiaqi Zhao, Byunghyun Ahn, and Hening Lin. Loss of diphthamide increases dna replication stress in mammalian cells by modulating the translation of rrm1. ACS Central Science, 10:1835-1847, Sep 2024. URL: https://doi.org/10.1021/acscentsci.4c00967, doi:10.1021/acscentsci.4c00967. This article has 5 citations and is from a highest quality peer-reviewed journal.

  5. (su2013thediscoveryand pages 16-21): X Su. The discovery and functional studies of two diphthamide biosynthetic genes. Unknown journal, 2013.

  6. (su2013thediscoveryand pages 108-116): X Su. The discovery and functional studies of two diphthamide biosynthetic genes. Unknown journal, 2013.

  7. (utkur2024functionalintegrityof pages 1-2): Koray Ütkür, Klaus Mayer, Shihui Liu, Ulrich Brinkmann, and Raffael Schaffrath. Functional integrity of radical sam enzyme dph1•dph2 requires non-canonical cofactor motifs with tandem cysteines. Biomolecules, Apr 2024. URL: https://doi.org/10.3390/biom14040470, doi:10.3390/biom14040470. This article has 1 citations.

  8. (utkur2024functionalintegrityof pages 2-4): Koray Ütkür, Klaus Mayer, Shihui Liu, Ulrich Brinkmann, and Raffael Schaffrath. Functional integrity of radical sam enzyme dph1•dph2 requires non-canonical cofactor motifs with tandem cysteines. Biomolecules, Apr 2024. URL: https://doi.org/10.3390/biom14040470, doi:10.3390/biom14040470. This article has 1 citations.

  9. (utkur2023dph1anddph2 pages 9-10): Koray Ütkür, Klaus Mayer, Maliha Khan, Thirishika Manivannan, Raffael Schaffrath, and Ulrich Brinkmann. Dph1 and dph2 variants that confer susceptibility to diphthamide deficiency syndrome in human cells and yeast models. Disease Models & Mechanisms, Sep 2023. URL: https://doi.org/10.1242/dmm.050207, doi:10.1242/dmm.050207. This article has 9 citations and is from a domain leading peer-reviewed journal.

  10. (su2013thebiosynthesisand pages 10-14): Xiaoyang Su, Zhewang Lin, and Hening Lin. The biosynthesis and biological function of diphthamide. Critical Reviews in Biochemistry and Molecular Biology, 48:515-521, Nov 2013. URL: https://doi.org/10.3109/10409238.2013.831023, doi:10.3109/10409238.2013.831023. This article has 94 citations and is from a peer-reviewed journal.

  11. (zhang2025diphthamideformationin pages 1-4): Hongliang Zhang, Nadežda Janina, Koray Ütkür, Thirishika Manivannan, Lei Zhang, Lizhen Wang, Christopher Grefen, Raffael Schaffrath, and Ute Krämer. Diphthamide formation in arabidopsis requires dph1-interacting dph2 for light and oxidative stress resistance. Sep 2025. URL: https://doi.org/10.1101/2024.09.16.613322, doi:10.1101/2024.09.16.613322. This article has 2 citations.

  12. (utkur2023dph1anddph2 pages 4-5): Koray Ütkür, Klaus Mayer, Maliha Khan, Thirishika Manivannan, Raffael Schaffrath, and Ulrich Brinkmann. Dph1 and dph2 variants that confer susceptibility to diphthamide deficiency syndrome in human cells and yeast models. Disease Models & Mechanisms, Sep 2023. URL: https://doi.org/10.1242/dmm.050207, doi:10.1242/dmm.050207. This article has 9 citations and is from a domain leading peer-reviewed journal.

Artifacts

Citations

  1. liu2004identificationofthe pages 1-2
  2. su2013thebiosynthesisand pages 3-4
  3. zhang2025diphthamideformationin pages 1-4
  4. utkur2024functionalintegrityof pages 1-2
  5. zhao2024lossofdiphthamide pages 1-2
  6. utkur2024functionalintegrityof pages 2-4
  7. su2013thediscoveryand pages 16-21
  8. su2013thediscoveryand pages 108-116
  9. su2013thebiosynthesisand pages 10-14
  10. https://doi.org/10.1128/mcb.24.21.9487-9497.2004;
  11. https://doi.org/10.3109/10409238.2013.831023;
  12. https://doi.org/10.1242/dmm.050207
  13. https://doi.org/10.3109/10409238.2013.831023
  14. https://doi.org/10.3390/biom14040470
  15. https://doi.org/10.1242/dmm.050207;
  16. https://doi.org/10.1021/acscentsci.4c00967
  17. https://doi.org/10.1021/acscentsci.4c00967;
  18. https://doi.org/10.1128/mcb.24.21.9487-9497.2004
  19. https://doi.org/10.1128/mcb.24.21.9487-9497.2004,
  20. https://doi.org/10.3109/10409238.2013.831023,
  21. https://doi.org/10.1242/dmm.050207,
  22. https://doi.org/10.1021/acscentsci.4c00967,
  23. https://doi.org/10.3390/biom14040470,
  24. https://doi.org/10.1101/2024.09.16.613322,

📚 Additional Documentation

Notes

(dph2-notes.md)

dph2 (Danio rerio) -- Research Notes

Gene Identity

  • UniProt: A4QN59 (DPH2_DANRE)
  • Full name: 2-(3-amino-3-carboxypropyl)histidine synthase subunit 2
  • Synonyms: Diphthamide biosynthesis protein 2, Diphtheria toxin resistance protein 2
  • Organism: Danio rerio (zebrafish)
  • Chromosome 7

Summary of Function

Dph2 is a subunit of the heterodimeric Dph1-Dph2 complex that catalyzes the first committed step in diphthamide biosynthesis: the transfer of a 3-amino-3-carboxypropyl (ACP) group from S-adenosyl-L-methionine (SAM) to a conserved histidine residue (His715 in mammals) of eukaryotic translation elongation factor 2 (eEF2). This is a unique post-translational modification found only on eEF2, conserved from archaea to humans.

Biochemistry and Mechanism

The Dph1-Dph2 heterodimer is a noncanonical radical SAM enzyme. In archaea, the equivalent activity is performed by a Dph2 homodimer (e.g., Pyrococcus horikoshii PhDph2), whereas in eukaryotes a Dph1-Dph2 heterodimer carries out the reaction [PMID:20559380, "Diphthamide biosynthesis requires an organic radical generated by an iron-sulphur enzyme"].

The catalytic mechanism involves the [4Fe-4S] cluster in Dph1 (not Dph2) attacking the gamma-carbon of methionine in SAM, generating an organometallic ACP-[4Fe-4S] intermediate and 5'-methylthioadenosine (MTA). In the presence of eEF2, homolytic cleavage of the Fe-C bond releases the ACP radical, which reacts with the target histidine [PMID:29590073, "organometallic and radical intermediates reveal mechanism of diphthamide biosynthesis"].

Dph2 binds its own [4Fe-4S] cluster (at Cys89, Cys110, Cys341 in zebrafish, by similarity to yeast P32461). The Dph2 cluster does not perform the radical chemistry but instead facilitates the reduction of the catalytic [4Fe-4S] cluster in Dph1 [UniProt A4QN59, "Facilitates the reduction of the catalytic iron-sulfur cluster found in the dph1 subunit"].

Dph3 (also known as KTI11) serves as the physiological electron donor for the Dph1-Dph2 complex, reducing the iron-sulfur cluster required for catalysis [PMID:24422557, "Dph3 is an electron donor for Dph1-Dph2 in the first step of eukaryotic diphthamide biosynthesis"]. Under aerobic conditions, Dph3 also donates an iron atom to convert a degraded [3Fe-4S] cluster back to a functional [4Fe-4S] cluster in the Dph1-Dph2 complex [PMID:34154323, "Dph3 Enables Aerobic Diphthamide Biosynthesis by Donating One Iron Atom to Transform a [3Fe-4S] to a [4Fe-4S] Cluster in Dph1-Dph2"].

Pathway Context

The full diphthamide biosynthesis pathway requires seven proteins (DPH1-DPH7):
- Step 1 (DPH1, DPH2, DPH3, DPH4): Transfer of ACP group from SAM to His715 of eEF2
- Step 2 (DPH5): Trimethylation of ACP-histidine
- Step 3 (DPH6, DPH7): Demethylation and amidation to form mature diphthamide

Reactome pathway: R-DRE-5358493 "Synthesis of diphthamide-EEF2"

Biological Significance

Diphthamide modification of eEF2 ensures translational fidelity. Loss of diphthamide increases ribosomal frameshifting [PMID:38097404, "Diphthamide - a conserved modification of eEF2 with clinical relevance"]. The modification is also the target of bacterial ADP-ribosylating toxins including diphtheria toxin and Pseudomonas exotoxin A.

Disease and Developmental Relevance

Biallelic loss-of-function variants in human DPH1 or DPH2 cause "diphthamide-deficiency syndrome," an autosomal recessive developmental disorder characterized by intellectual disability, seizures, short stature, craniofacial dysmorphism, and congenital heart defects [PMID:32576952, "Diphthamide-deficiency syndrome: a novel human developmental disorder and ribosomopathy"]. Specific DPH2 variants (H105P, C341Y) have been shown to abolish diphthamide biosynthesis in human cells and yeast models [PMID:37675463, "DPH1 and DPH2 variants that confer susceptibility to diphthamide deficiency syndrome in human cells and yeast models"].

In mouse models, Dph1 deficiency promotes eEF2 dissociation from ribosomes and association with p53 to drive p21 expression and neural crest defects [PMID:38671004, "Diphthamide deficiency promotes association of eEF2 with p53 to induce p21 expression and neural crest defects"].

Key References

  • PMID:20559380 - Zhang et al. (2010) Nature. Radical mechanism of diphthamide biosynthesis.
  • PMID:29590073 - Dong et al. (2018) Science. Organometallic and radical intermediates.
  • PMID:24422557 - Dong et al. (2014) JACS. Dph3 as electron donor for Dph1-Dph2.
  • PMID:34154323 - Dong et al. (2021) JACS. Dph3 iron atom donation for aerobic diphthamide biosynthesis.
  • PMID:32576952 - Hawer et al. (2020) Eur J Hum Genet. Diphthamide-deficiency syndrome.
  • PMID:37675463 - Hawer et al. (2023) Dis Model Mech. DPH1/DPH2 variant analysis.
  • PMID:38671004 - Yu et al. (2024) Nat Commun. eEF2-p53 association and neural crest defects.
  • PMID:38097404 - Hawer et al. (2024) Trends Mol Med. Diphthamide review with clinical relevance.

Bioreason Sft Review

(dph2-bioreason-sft-review.md)

BioReason-Pro SFT Review: dph2 (Danio rerio)

Source: dph2-deep-research-bioreason-sft.md

  • Correctness: 3/5
  • Completeness: 4/5

Functional Summary Review

The BioReason SFT functional summary states:

A nucleocytoplasmic adaptor that organizes the first step of the diphthamide modification on the histidine of translation elongation factor 2. It binds the radical-generating enzyme and the ferredoxin-based electron-delivery system, aligns eEF2 for precise chemistry, and thereby enables formation of the amino-aldehyde side chain on the target histidine. By ensuring efficient eEF2 modification, it supports accurate translation and influences developmental programs, including cartilage formation.

Correctly captured:
- Dph2 participates in the first step of diphthamide modification on eEF2. This is the central and best-established function.
- The involvement of a radical-generating enzyme (Dph1) and electron delivery system is correctly noted.
- The connection between diphthamide and translational accuracy is supported by literature.

Errors and overstatements:

  1. "non-enzymatic adaptor" framing is misleading. The thinking trace states the protein is "a conserved, non-enzymatic adaptor specialized for the diphthamide pathway" and claims "the absence of catalytic domain signatures" argues the protein's function is "to bind other proteins and organize a redox-coupled transfer reaction rather than to perform the chemistry itself." While it is true that the radical SAM chemistry resides primarily in Dph1, Dph2 does bind a [4Fe-4S] cluster (confirmed by three conserved cysteines and by similarity to yeast P32461) and contributes to the enzymatic activity of the complex. Calling it merely an "adaptor" undersells its biochemical role. The ISS annotation in GOA correctly uses contributes_to for the ACP synthase activity, which is more accurate than "adaptor."

  2. "amino-aldehyde side chain" is incorrect chemistry. The product of the first step is a 3-(3-amino-3-carboxypropyl)histidine, not an amino-aldehyde. Diphthamide is an amide, not an aldehyde. This is a factual chemical error.

  3. "cartilage formation" is weakly supported for dph2 specifically. The thinking trace infers GO:0051216 (cartilage development) based on general vertebrate diphthamide biology. While diphthamide deficiency does cause developmental defects including craniofacial features (PMID:32576952) and neural crest defects (PMID:38671004), the link to cartilage specifically has not been demonstrated for dph2, and the developmental phenotypes are better described as neural crest-related rather than cartilage-specific. This appears to be an over-annotation.

  4. Nuclear localization claim is speculative. The trace suggests "A nuclear pool is also plausible because eEF2 shuttles" but provides no evidence for nuclear localization of Dph2 itself. There is no experimental or computational support for dph2 being in the nucleus. All characterized diphthamide biosynthesis occurs in the cytoplasm.

  5. "protein binding" (GO:0005515) as "core activity" is unhelpful. The BioReason trace explicitly calls protein binding a core activity. Per curation guidelines, GO:0005515 is uninformative. The relevant molecular function is the specific contribution to ACP synthase activity and [4Fe-4S] cluster binding.

Comparison with InterPro2GO

The InterPro2GO annotation (GO_REF:0000002) assigns:
- GO:0090560 (2-(3-amino-3-carboxypropyl)histidine synthase activity) from IPR016435

The BioReason SFT functional summary covers essentially the same ground as what InterPro2GO provides: the protein is part of the diphthamide biosynthesis machinery. However, BioReason adds narrative context about the electron delivery system (Dph3, ferredoxin), the developmental consequences, and the complex architecture. These additions show some biological insight beyond simple domain-to-function mapping.

Where BioReason diverges from InterPro2GO, it is sometimes wrong: the InterPro2GO annotation does not claim nuclear localization or cartilage development. BioReason also introduces the "adaptor" framing which, while not entirely wrong, misrepresents the enzymatic contribution that the ISS annotation correctly captures with the contributes_to qualifier.

Overall, the BioReason SFT output provides a reasonable narrative summary that goes modestly beyond InterPro2GO recapitulation, but introduces several inaccuracies (chemical nomenclature, nuclear localization, cartilage claim) that reduce confidence. The core biological story -- Dph2 as a subunit of the diphthamide biosynthesis complex -- is correctly conveyed.

Notes on Thinking Trace

The thinking trace shows a structured domain-to-function reasoning approach: it reads the InterPro domains, infers molecular function, then biological process, then cellular component. This is methodical but leads to overconfidence in speculative inferences (nuclear localization from general eEF2 shuttling, cartilage development from vertebrate developmental phenotypes).

The trace correctly identifies the key partners (DPH1, DPH3, DPH5-7, eEF2) and the electron transfer chain. It also correctly notes the [4Fe-4S] cluster involvement. However, the insistence that Dph2 is "non-enzymatic" and functions purely as an "adaptor" contradicts the evidence that Dph2 binds its own iron-sulfur cluster and contributes to the catalytic activity, as captured by the contributes_to qualifier in GOA.

📄 View Raw YAML

id: A4QN59
gene_symbol: dph2
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:7955
  label: Danio rerio
description: >-
  Dph2 is a subunit of the Dph1-Dph2 heterodimeric complex that catalyzes the
  first step of diphthamide biosynthesis, the transfer of a 3-amino-3-carboxypropyl
  (ACP) group from S-adenosyl-L-methionine to a conserved histidine of eukaryotic
  translation elongation factor 2 (eEF2). Dph2 binds a [4Fe-4S] cluster that
  facilitates reduction of the catalytic iron-sulfur cluster in the Dph1 subunit.
  Diphthamide is a unique post-translational modification of eEF2 that ensures
  translational fidelity and is the target of diphtheria toxin ADP-ribosylation.
  Loss of DPH2 function in humans causes diphthamide-deficiency syndrome, an
  autosomal recessive developmental disorder.
existing_annotations:
- term:
    id: GO:0017183
    label: protein histidyl modification to diphthamide
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: Phylogenetic inference from orthologs in yeast (DPH1, DPH2) and
      mouse correctly places dph2 in the diphthamide biosynthesis pathway. The
      DPH1-DPH2 heterodimer catalyzes the first step of diphthamide synthesis
      on eEF2, a pathway conserved from archaea to vertebrates.
    action: ACCEPT
    supported_by:
      - reference_id: PMID:32576952
        supporting_text: >-
          The gene products DPH1 and DPH2 are components of a heterodimeric
          enzyme complex that mediates the first step of the posttranslational
          diphthamide modification on the nonredundant eukaryotic translation
          elongation factor 2 (eEF2)
      - reference_id: file:DANRE/dph2/dph2-deep-research-falcon.md
        supporting_text: >-
          DPH2 (together with DPH1) functions in the ...first committed step...
          of diphthamide biosynthesis: transfer of a ...3-amino-3-carboxypropyl (ACP)...
          group derived from ...S-adenosylmethionine (SAM/AdoMet)... onto the
          ...C2 of the imidazole ring... of a conserved eEF2 histidine. This ACP
          addition generates an early diphthamide-pathway intermediate on eEF2
- term:
    id: GO:0017183
    label: protein histidyl modification to diphthamide
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: Combined automated annotation from InterPro domain matches
      (IPR010014, IPR016435) and UniPathway correctly assigns diphthamide
      biosynthesis. Consistent with the well-characterized biochemical role
      of DPH2 family proteins.
    action: ACCEPT
    supported_by:
      - reference_id: PMID:20559380
        supporting_text: >-
          Diphthamide biosynthesis requires an organic radical generated by
          an iron-sulphur enzyme
- term:
    id: GO:0090560
    label: 2-(3-amino-3-carboxypropyl)histidine synthase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: InterPro2GO mapping from IPR016435 (Diphthamide synthesis DPH1/DPH2
      family) assigns the ACP synthase activity with an implicit enables qualifier.
      However, Dph2 does not independently catalyze the reaction; the radical
      chemistry resides in the Dph1 subunit. The ISS annotation (below) correctly
      uses contributes_to. This IEA annotation over-annotates by implying Dph2
      independently enables the activity.
    action: MARK_AS_OVER_ANNOTATED
    reason: The IEA annotation assigns the full enables qualifier, but Dph2 only
      contributes to the complex activity. The ISS annotation with contributes_to
      qualifier is the correct representation.
    supported_by:
      - reference_id: PMID:20559380
        supporting_text: >-
          Diphthamide biosynthesis requires an organic radical generated by
          an iron-sulphur enzyme
      - reference_id: PMID:24422557
        supporting_text: >-
          Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent
          to the homodimer of PhDph2 and is sufficient to catalyze the first
          step in vitro in the presence of dithionite as the reductant
- term:
    id: GO:0120513
    label: 2-(3-amino-3-carboxypropyl)histidine synthase complex
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: Sequence similarity transfer from yeast DPH2 (P32461). Dph2 is
      a subunit of the Dph1-Dph2 heterodimer in eukaryotes, which together
      with Dph3 and NADH-dependent reductase forms the ACP synthase complex.
      Well supported by biochemical evidence in yeast and archaea.
    action: ACCEPT
    supported_by:
      - reference_id: PMID:24422557
        supporting_text: >-
          Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent
          to the homodimer of PhDph2 and is sufficient to catalyze the first
          step in vitro
      - reference_id: file:DANRE/dph2/dph2-deep-research-falcon.md
        supporting_text: >-
          Modern pathway summaries indicate the initial step is catalyzed by
          an Fe–S DPH1/DPH2 heterodimer, with involvement of DPH3/DPH4 in
          supporting the reaction
- term:
    id: GO:0017183
    label: protein histidyl modification to diphthamide
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: Sequence similarity transfer from yeast DPH2 (P32461). This
      duplicates the IBA and IEA annotations for the same term but with ISS
      evidence. The annotation is correct as DPH2 is required for diphthamide
      biosynthesis.
    action: ACCEPT
    supported_by:
      - reference_id: PMID:32576952
        supporting_text: >-
          The gene products DPH1 and DPH2 are components of a heterodimeric
          enzyme complex that mediates the first step of the posttranslational
          diphthamide modification on the nonredundant eukaryotic translation
          elongation factor 2 (eEF2)
- term:
    id: GO:0051539
    label: 4 iron, 4 sulfur cluster binding
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: Sequence similarity transfer from yeast DPH2 (P32461). The
      zebrafish Dph2 has three conserved cysteine residues (Cys89, Cys110,
      Cys341) that coordinate a [4Fe-4S] cluster, as annotated in UniProt
      by similarity. The Dph2 cluster facilitates reduction of the catalytic
      cluster in Dph1 rather than directly participating in radical chemistry.
    action: ACCEPT
    supported_by:
      - reference_id: PMID:34154323
        supporting_text: >-
          all radical S-adenosylmethionine (radical-SAM) enzymes, including
          the noncanonical radical-SAM enzyme diphthamide biosynthetic enzyme
          Dph1-Dph2, require at least one [4Fe-4S](Cys)3 cluster for activity
      - reference_id: file:DANRE/dph2/dph2-deep-research-falcon.md
        supporting_text: >-
          One Fe-S cluster per subunit; atypical cysteine motifs instead of
          canonical CX3CX2C radical-SAM motif
- term:
    id: GO:0090560
    label: 2-(3-amino-3-carboxypropyl)histidine synthase activity
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: contributes_to
  review:
    summary: Sequence similarity transfer from yeast DPH2 (P32461) with
      the correct contributes_to qualifier. Dph2 is required for ACP synthase
      activity as part of the Dph1-Dph2 complex but does not independently
      catalyze the radical SAM reaction. The contributes_to qualifier
      appropriately reflects that Dph1 houses the catalytic [4Fe-4S] cluster.
    action: ACCEPT
    supported_by:
      - reference_id: PMID:29590073
        supporting_text: >-
          Diphthamide biosynthesis involves a carbon-carbon bond-forming reaction
          catalyzed by a radical S-adenosylmethionine (SAM) enzyme that cleaves a
          carbon-sulfur (C-S) bond in SAM to generate a 3-amino-3-carboxypropyl
          (ACP) radical
      - reference_id: PMID:24422557
        supporting_text: >-
          Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent
          to the homodimer of PhDph2 and is sufficient to catalyze the first
          step in vitro in the presence of dithionite as the reductant
      - reference_id: file:DANRE/dph2/dph2-deep-research-falcon.md
        supporting_text: >-
          Dph1 and Dph2 are homologous and are thought to form a ...heterodimer...
          that is functionally analogous to archaeal homodimeric Dph2
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: ISS
  review:
    summary: Dph2 functions in the cytoplasm where it forms a complex with Dph1
      to modify cytoplasmic eEF2. The diphthamide biosynthesis machinery operates
      on eEF2 in the cytosol, consistent with its role in translation elongation.
      No transmembrane domains or signal peptides are present.
    action: NEW
    reason: Cytoplasmic localization is implied by the function of the Dph1-Dph2
      complex on cytosolic eEF2 but was not explicitly annotated in GOA. The
      BioReason SFT analysis also identified cytoplasmic localization.
    supported_by:
      - reference_id: file:DANRE/dph2/dph2-deep-research-bioreason-sft.md
        supporting_text: >-
          The cellular component is dictated by where eEF2 resides and where
          ferredoxin-coupled redox partners operate. The adaptor must access
          cytosolic eEF2 and the cytosolic ferredoxin/reductase chain, supporting
          localization to the GO:0005737 cytoplasm
      - reference_id: file:DANRE/dph2/dph2-deep-research-falcon.md
        supporting_text: >-
          diphthamide is a modification on the ...cytosolic translation factor
          eEF2..., so the pathway is expected to act in the ...cytosol...
          ...Arabidopsis DPH2 localizes to the cytosol and physically interacts
          with DPH1..., consistent with a cytosolic biosynthetic complex acting
          on cytosolic eEF2
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to
    orthologs by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:20559380
  title: Diphthamide biosynthesis requires an organic radical generated by an
    iron-sulphur enzyme
  full_text_unavailable: true
  findings:
    - statement: The Dph2 enzyme in Pyrococcus horikoshii uses a [4Fe-4S] cluster
        to generate an organic radical from SAM for diphthamide biosynthesis
      supporting_text: >-
        Diphthamide biosynthesis requires an organic radical generated by an
        iron-sulphur enzyme
      reference_section_type: ABSTRACT
- id: PMID:29590073
  title: Organometallic and radical intermediates reveal mechanism of diphthamide
    biosynthesis
  full_text_unavailable: true
  findings:
    - statement: The diphthamide biosynthetic enzyme generates an organometallic
        intermediate with an iron-carbon bond between ACP and the [4Fe-4S] cluster,
        followed by a product-like radical on eEF2
      supporting_text: >-
        Diphthamide biosynthesis involves a carbon-carbon bond-forming reaction
        catalyzed by a radical S-adenosylmethionine (SAM) enzyme that cleaves a
        carbon-sulfur (C-S) bond in SAM to generate a 3-amino-3-carboxypropyl
        (ACP) radical
      reference_section_type: ABSTRACT
- id: PMID:24422557
  title: Dph3 is an electron donor for Dph1-Dph2 in the first step of eukaryotic
    diphthamide biosynthesis
  full_text_unavailable: true
  findings:
    - statement: Dph3 (KTI11) serves as the physiological electron donor to reduce
        the [4Fe-4S] cluster in the Dph1-Dph2 complex
      supporting_text: >-
        Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent to
        the homodimer of PhDph2 and is sufficient to catalyze the first step
        in vitro in the presence of dithionite as the reductant
      reference_section_type: ABSTRACT
- id: PMID:34154323
  title: Dph3 enables aerobic diphthamide biosynthesis by donating one iron atom to
    transform a [3Fe-4S] to a [4Fe-4S] cluster in Dph1-Dph2
  full_text_unavailable: true
  findings:
    - statement: Dph3 donates an iron atom to restore a functional [4Fe-4S] cluster
        in the Dph1-Dph2 complex under aerobic conditions
      supporting_text: >-
        all radical S-adenosylmethionine (radical-SAM) enzymes, including the
        noncanonical radical-SAM enzyme diphthamide biosynthetic enzyme
        Dph1-Dph2, require at least one [4Fe-4S](Cys)3 cluster for activity
      reference_section_type: ABSTRACT
- id: PMID:32576952
  title: Diphthamide-deficiency syndrome -- a novel human developmental disorder and
    ribosomopathy
  full_text_unavailable: true
  findings:
    - statement: Biallelic DPH2 mutations cause diphthamide-deficiency syndrome with
        intellectual disability, seizures, and developmental abnormalities
      supporting_text: >-
        The gene products DPH1 and DPH2 are components of a heterodimeric
        enzyme complex that mediates the first step of the posttranslational
        diphthamide modification on the nonredundant eukaryotic translation
        elongation factor 2 (eEF2)
      reference_section_type: ABSTRACT
- id: PMID:37675463
  title: DPH1 and DPH2 variants that confer susceptibility to diphthamide deficiency
    syndrome in human cells and yeast models
  full_text_unavailable: true
  findings:
    - statement: DPH2 variants H105P and C341Y abolish diphthamide biosynthesis,
        confirmed in human cells and yeast functional assays
      supporting_text: >-
        Ten additional human DPH1...and two DPH2 (H105P, C341Y) variants
        showed reduced functionality and hence are deficiency-susceptibility
        alleles
      reference_section_type: ABSTRACT
- id: PMID:38671004
  title: Diphthamide deficiency promotes association of eEF2 with p53 to induce p21
    expression and neural crest defects
  full_text_unavailable: true
  findings:
    - statement: Diphthamide deficiency causes eEF2 to dissociate from ribosomes and
        associate with p53, driving p21-mediated growth arrest and neural crest defects
      supporting_text: >-
        DPH1 depletion facilitates dissociation of eEF2 from ribosomes and
        association with p53 to promote transcription of the cell cycle
        inhibitor p21, resulting in inhibited proliferation
      reference_section_type: ABSTRACT
- id: PMID:38097404
  title: Diphthamide -- a conserved modification of eEF2 with clinical relevance
  full_text_unavailable: true
  findings:
    - statement: Comprehensive review of diphthamide as a conserved eEF2 modification
        affecting translational fidelity, viral susceptibility, and human disease
      supporting_text: >-
        Diphthamide, a complex modification on eukaryotic translation elongation
        factor 2 (eEF2), assures reading-frame fidelity during translation
      reference_section_type: ABSTRACT
- id: file:DANRE/dph2/dph2-deep-research-bioreason-sft.md
  title: BioReason SFT reasoning trace for dph2 (Danio rerio)
  findings:
    - statement: BioReason SFT identifies dph2 as a nucleocytoplasmic adaptor for
        diphthamide biosynthesis that organizes the Dph1-Dph2-Dph3 complex
- id: file:DANRE/dph2/dph2-deep-research-falcon.md
  title: Falcon deep research for zebrafish dph2 (Danio rerio, A4QN59)
  findings:
    - statement: >-
        No zebrafish-specific primary studies naming UniProt A4QN59 or zgc:162269
        were retrieved; functional assignments are based on highly conserved,
        mechanistically characterized eukaryotic/archaeal DPH2 homologs given the
        strong conservation of the diphthamide biosynthesis pathway from archaea
        to humans.
      supporting_text: >-
        I did ...not... find zebrafish-specific primary studies explicitly naming
        UniProt A4QN59 or zgc:162269; therefore, organism-specific phenotypes or
        expression patterns for zebrafish are not asserted here. Functional
        statements are based on ...highly conserved, mechanistically characterized
        eukaryotic/archaeal DPH2 homologs...
    - statement: >-
        Dph2, with Dph1, catalyzes the first committed step of diphthamide
        biosynthesis - transfer of the 3-amino-3-carboxypropyl (ACP) group from
        SAM onto the imidazole C2 of a conserved eEF2 histidine.
      supporting_text: >-
        DPH2 (together with DPH1) functions in the ...first committed step...
        of diphthamide biosynthesis: transfer of a ...3-amino-3-carboxypropyl (ACP)...
        group derived from ...S-adenosylmethionine (SAM/AdoMet)... onto the
        ...C2 of the imidazole ring... of a conserved eEF2 histidine
    - statement: >-
        The Dph1-Dph2 catalytic module is a non-canonical radical-SAM enzyme that
        uses Fe-S clusters but does not employ the canonical CX3CX2C motif and
        generates an ACP radical rather than the classical 5'-deoxyadenosyl radical.
      supporting_text: >-
        it uses Fe–S clusters but does ...not... rely on the canonical ...CX3CX2C...
        motif and does ...not... generate the classical 5′-deoxyadenosyl radical;
        instead it generates an ...ACP radical... from SAM cleavage that is then
        used to functionalize eEF2 histidine
    - statement: >-
        Diphthamide on eEF2 supports translational fidelity and suppresses spurious
        -1 frameshifting; in mammalian cells its loss perturbs RRM1 translation and
        elevates DNA replication stress.
      supporting_text: >-
        Mature diphthamide on eEF2 supports translational fidelity and suppresses
        spurious -1 frameshifting; deficiency perturbs translation of proteins
        such as RRM1 and elevates DNA replication stress
    - statement: >-
        Dph2 acts in the cytosol on cytosolic eEF2; experimental cytosolic
        localization of Arabidopsis DPH2 (interacting with DPH1) supports this
        expectation for the conserved complex.
      supporting_text: >-
        Arabidopsis DPH2 localizes to the cytosol and physically interacts with
        DPH1..., consistent with a cytosolic biosynthetic complex acting on
        cytosolic eEF2
core_functions:
  - description: >-
      Subunit of the Dph1-Dph2 heterodimer that catalyzes transfer of a
      3-amino-3-carboxypropyl group from SAM to a conserved histidine of eEF2,
      the first committed step in diphthamide biosynthesis. Dph2 binds a [4Fe-4S]
      cluster that facilitates reduction of the catalytic cluster in Dph1, while
      Dph1 performs the radical SAM chemistry. The resulting diphthamide
      modification ensures translational reading frame fidelity.
    molecular_function:
      id: GO:0051539
      label: 4 iron, 4 sulfur cluster binding
    contributes_to_molecular_function:
      id: GO:0090560
      label: 2-(3-amino-3-carboxypropyl)histidine synthase activity
    directly_involved_in:
      - id: GO:0017183
        label: protein histidyl modification to diphthamide
    locations:
      - id: GO:0005737
        label: cytoplasm
    in_complex:
      id: GO:0120513
      label: 2-(3-amino-3-carboxypropyl)histidine synthase complex
    supported_by:
      - reference_id: PMID:24422557
        supporting_text: >-
          Yeast Dph1 and Dph2 form a complex (Dph1-Dph2) that is equivalent
          to the homodimer of PhDph2 and is sufficient to catalyze the first
          step in vitro in the presence of dithionite as the reductant
      - reference_id: PMID:29590073
        supporting_text: >-
          Diphthamide biosynthesis involves a carbon-carbon bond-forming reaction
          catalyzed by a radical S-adenosylmethionine (SAM) enzyme that cleaves a
          carbon-sulfur (C-S) bond in SAM to generate a 3-amino-3-carboxypropyl
          (ACP) radical
      - reference_id: PMID:34154323
        supporting_text: >-
          all radical S-adenosylmethionine (radical-SAM) enzymes, including
          the noncanonical radical-SAM enzyme diphthamide biosynthetic enzyme
          Dph1-Dph2, require at least one [4Fe-4S](Cys)3 cluster for activity
      - reference_id: file:DANRE/dph2/dph2-deep-research-falcon.md
        supporting_text: >-
          Mature diphthamide on eEF2 supports translational fidelity and suppresses
          spurious -1 frameshifting
suggested_questions:
  - question: Is there direct experimental evidence for dph2 function in zebrafish,
      or are all functional assignments based on orthology to yeast and human DPH2?
  - question: Does zebrafish dph2 deficiency produce neural crest or craniofacial
      phenotypes analogous to those seen in mouse Dph1 knockin models?
  - question: Is the [4Fe-4S] cluster in zebrafish dph2 essential for its function,
      and does Dph3-mediated iron donation operate similarly in fish?
suggested_experiments:
  - description: CRISPR-Cas9 knockout of dph2 in zebrafish embryos to assess
      developmental phenotypes, particularly craniofacial and neural crest
      derivatives, with comparison to dph1 mutants
  - description: In vitro reconstitution of zebrafish Dph1-Dph2 complex to confirm
      ACP transferase activity and [4Fe-4S] cluster requirements using
      site-directed mutagenesis of the three conserved cysteine residues