QDPR encodes dihydropteridine reductase (DHPR; EC 1.5.1.34), a cytosolic, homodimeric NAD(P)H-dependent oxidoreductase of the short-chain dehydrogenase/reductase (SDR) family. DHPR regenerates the essential cofactor tetrahydrobiopterin (BH4) by reducing the quinonoid form of dihydrobiopterin (q-BH2) back to BH4, completing the pterin cofactor cycle. BH4 is the obligate cofactor of the aromatic amino acid hydroxylases (phenylalanine, tyrosine and tryptophan hydroxylases) and of nitric oxide synthases, so DHPR-mediated BH4 salvage is required for phenylalanine catabolism and for biosynthesis of the monoamine neurotransmitters dopamine and serotonin. The enzyme adopts a Rossmann NAD(P)-binding fold with a catalytic tyrosine (Tyr150), and its structure has been solved by X-ray crystallography. In humans, biallelic loss-of-function variants in QDPR abolish BH4 regeneration and cause autosomal recessive dihydropteridine reductase deficiency, a BH4-deficient ("malignant"/atypical) hyperphenylalaninemia with progressive neurological disease driven by combined hyperphenylalaninemia and monoamine neurotransmitter deficiency.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004155 6,7-dihydropteridine reductase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Core molecular function. The phylogenetically inferred (IBA) DHPR activity is the enzyme's defining, experimentally established catalytic function (EC 1.5.1.34): NAD(P)H-dependent reduction of quinonoid dihydropteridine to tetrahydropteridine, regenerating BH4. Reason: Consistent with direct experimental evidence and UniProt catalytic activity. This term at exactly the right level of specificity for the gene. Supporting Evidence: PMID:3033643 Dihydropteridine reductase (DHPR; EC 1.6.99.7) catalyzes the NADH-mediated reduction of quinonoid dihydrobiopterin and is an essential component of the pterin-dependent aromatic amino acid hydroxylating systems. |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: DHPR is a soluble cytosolic enzyme; the phylogenetic is_active_in cytoplasm annotation is consistent with the enzyme acting in the cytosolic BH4 salvage cycle that supplies the cytosolic aromatic amino acid hydroxylases. Reason: Cytoplasmic/cytosolic localization is well supported (IDA to cytoplasm, TAS to cytosol) and is the physiologically relevant compartment. The more specific GO:0005829 cytosol is also annotated and captured in core_functions. Supporting Evidence: file:human/QDPR/QDPR-uniprot.txt Catalyzes the conversion of quinonoid dihydrobiopterin into |
| GO:0006729 tetrahydrobiopterin biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: Core biological process. DHPR regenerates BH4 (the reduced, active pterin cofactor) from its quinonoid dihydro form, i.e. the salvage/regeneration arm of BH4 metabolism that this term subsumes. Reason: Directly supported: DHPR catalyzes formation of tetrahydrobiopterin from quinonoid dihydrobiopterin. This is the enzyme's principal pathway role. Supporting Evidence: file:human/QDPR/QDPR-uniprot.txt Catalyzes the conversion of quinonoid dihydrobiopterin into PMID:3033643 reduction of quinonoid dihydrobiopterin and is an essential component of the |
| GO:0070402 NADPH binding | IBA GO_REF:0000033 | ACCEPT | Summary: DHPR uses reduced nicotinamide cofactor as the hydride donor. UniProt records an NADP(+)/NADPH-dependent catalytic activity (RHEA:17865) in addition to the NADH-dependent reaction, supporting NADPH binding. Reason: Supported by the annotated NADP(+)-dependent catalytic activity and the Rossmann NAD(P)-binding fold with an NADP-binding region (residues 14-38). Supporting Evidence: file:human/QDPR/QDPR-uniprot.txt Reaction=5,6,7,8-tetrahydropteridine + NADP(+) = 6,7-dihydropteridine + |
| GO:0070404 NADH binding | IBA GO_REF:0000033 | ACCEPT | Summary: DHPR is classically the NADH-dependent quinonoid-dihydrobiopterin reductase; NADH is the physiological hydride donor and the crystal structure was solved as an NADH binary complex. Reason: Directly supported by the NADH-dependent catalytic activity and the structural characterization of the enzyme-NADH complex. Supporting Evidence: PMID:3033643 catalyzes the NADH-mediated PMID:8262916 and kinetic identity to the naturally occurring enzyme has been proven. |
| GO:0004155 6,7-dihydropteridine reductase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Automated (ARBA/EC/RHEA) assignment of the DHPR molecular function, mapped from EC 1.5.1.34 and RHEA:17865/17869. Correct and identical to the experimentally supported core function. Reason: IEA mapping from EC/RHEA is accurate and matches the experimental and IBA DHPR activity annotations. Supporting Evidence: file:human/QDPR/QDPR-uniprot.txt EC=1.5.1.34; Evidence={ECO:0000269|PubMed:3033643, |
| GO:0042558 pteridine-containing compound metabolic process | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: Broad but correct: DHPR acts on the pteridine cofactor biopterin (a pteridine-containing compound). More specific and informative terms (tetrahydrobiopterin biosynthetic process, dihydrobiopterin metabolic process) are also annotated. Reason: The term is accurate but high-level; it is a parent of the more specific BH4/dihydrobiopterin process terms that better capture the core role. Supporting Evidence: file:human/QDPR/QDPR-uniprot.txt Catalyzes the conversion of quinonoid dihydrobiopterin into |
| GO:0004155 6,7-dihydropteridine reductase activity | EXP PMID:8262916 The crystallographic structure of a human dihydropteridine r... | ACCEPT | Summary: Experimental support for DHPR activity from the enzyme that was purified to homogeneity, shown to have kinetic identity to the naturally occurring enzyme, and crystallized (PDB 1HDR). Reason: Direct experimental (kinetic/structural) evidence for the DHPR molecular function on the human enzyme. Supporting Evidence: PMID:8262916 and kinetic identity to the naturally occurring enzyme has been proven. |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | MARK AS OVER ANNOTATED | Summary: A single high-throughput mitochondrial-proteome mapping study lists QDPR among detected proteins. DHPR is an established soluble cytosolic SDR-family enzyme with no mitochondrial targeting features (initiator Met removed, N-acetylated Ala2, no transit peptide); it functions in the cytosolic BH4 salvage cycle. Reason: A single HTP proteomic detection is weak evidence for organellar residence of an abundant cytosolic enzyme, which is prone to co-purification. The catalytic function and its substrates/products are cytosolic; there is no corroborating evidence for a mitochondrial pool or function. Do not treat as core; flag as likely over-annotation rather than removing the curated HTP datum outright. Supporting Evidence: file:human/QDPR/QDPR-uniprot.txt Catalyzes the conversion of quinonoid dihydrobiopterin into |
| GO:0004155 6,7-dihydropteridine reductase activity | IDA PMID:3033643 Structure and expression of human dihydropteridine reductase... | ACCEPT | Summary: Direct assay evidence for human DHPR enzymatic activity: the isolated cDNA clone expressed in COS cells produced DHPR enzymatic activity, confirming the molecular function. Reason: IDA-level experimental confirmation of the core DHPR activity for the human enzyme. Supporting Evidence: PMID:3033643 Gene transfer of the recombinant human DHPR into COS cells leads to expression of DHPR enzymatic activity. |
| GO:0070062 extracellular exosome | HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres... | KEEP AS NON CORE | Summary: QDPR was detected in the shotgun proteome of prostatic-secretion (EPS) urinary exosomes. Detection of an abundant cytosolic enzyme in exosome proteomes is common and does not indicate a functional extracellular role. Reason: Valid HDA proteomic observation but not a site of DHPR catalytic function; the enzyme acts intracellularly in the cytosolic BH4 salvage cycle. Keep as a non-core localization datum. Supporting Evidence: PMID:23533145 exosome preparations were characterized by a shotgun proteomics procedure |
| GO:0070062 extracellular exosome | HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos... | KEEP AS NON CORE | Summary: QDPR was among the >1000 proteins identified by LC-MS/MS in the proteome of normal human urinary exosomes. As above, this reflects capture of an abundant cytosolic protein in exosomes rather than a functional extracellular localization. Reason: Corroborating HDA proteomic detection in exosomes; not a functional site of DHPR activity. Retain as non-core. Supporting Evidence: PMID:19056867 we used LC-MS/MS to profile the proteome of human urinary exosomes |
| GO:0005829 cytosol | TAS Reactome:R-HSA-71130 | ACCEPT | Summary: Cytosolic localization from Reactome, which curates the DHPR reaction (q-dihydrobiopterin + NADH + H+ => tetrahydrobiopterin + NAD+) in the cytosol. This is the physiologically relevant compartment for BH4 salvage. Reason: Cytosol is the correct, most specific localization for this soluble enzyme and matches the compartment of its substrates/products and the aromatic amino acid hydroxylases it serves. Supporting Evidence: file:human/QDPR/QDPR-uniprot.txt Catalyzes the conversion of quinonoid dihydrobiopterin into |
| GO:0005737 cytoplasm | IDA GO_REF:0000054 | ACCEPT | Summary: Direct localization of an expressed fusion protein to the cytoplasm (LIFEdb), consistent with the soluble cytosolic nature of DHPR. Reason: Consistent with all other localization evidence (cytosol/cytoplasm). The more specific cytosol term is retained in core_functions. Supporting Evidence: file:human/QDPR/QDPR-uniprot.txt Catalyzes the conversion of quinonoid dihydrobiopterin into |
| GO:0009055 electron transfer activity | TAS PMID:3033643 Structure and expression of human dihydropteridine reductase... | MODIFY | Summary: Generic electron-transfer function assigned by TAS. GO:0009055 denotes the directed movement of electrons between molecular entities typically mediated by electron carriers (as in electron transport chains). DHPR does not act as an electron carrier; it is an NAD(P)H-dependent oxidoreductase that transfers a hydride to a quinonoid pteridine (EC 1.5.1.34). Reason: The essence (a redox activity) is sound but the specific term is the wrong molecular function: DHPR's characterized activity is the 6,7-dihydropteridine reductase reaction, not electron-carrier transfer. The cited reference (PMID:3033643) describes NADH-mediated reduction of quinonoid dihydrobiopterin, i.e. the reductase activity. Replace with the specific reductase term (already annotated) so this generic term is not retained as a distinct function. Proposed replacements: 6,7-dihydropteridine reductase activity Supporting Evidence: PMID:3033643 catalyzes the NADH-mediated reduction of quinonoid dihydrobiopterin |
| GO:0004155 6,7-dihydropteridine reductase activity | TAS PMID:3033643 Structure and expression of human dihydropteridine reductase... | ACCEPT | Summary: Author-statement (TAS) support for the DHPR molecular function from the human DHPR cloning/expression paper, which describes the enzyme's NADH-mediated reduction of quinonoid dihydrobiopterin. Reason: Redundant with, and fully consistent with, the IDA/EXP/IBA/IEA DHPR activity annotations. Duplicate GO IDs across evidence codes are acceptable. Supporting Evidence: PMID:3033643 catalyzes the NADH-mediated reduction of quinonoid dihydrobiopterin |
| GO:0051066 dihydrobiopterin metabolic process | TAS PMID:3033643 Structure and expression of human dihydropteridine reductase... | ACCEPT | Summary: Accurate process term: DHPR metabolizes dihydrobiopterin, reducing its quinonoid form to BH4. This is a precise description of the enzyme's substrate-level role in the pterin cycle. Reason: Directly supported by the characterized reaction (quinonoid dihydrobiopterin reduction). Complements the tetrahydrobiopterin biosynthetic process term. Supporting Evidence: PMID:3033643 catalyzes the NADH-mediated reduction of quinonoid dihydrobiopterin |
| GO:0006520 amino acid metabolic process | TAS PMID:3033643 Structure and expression of human dihydropteridine reductase... | KEEP AS NON CORE | Summary: Very high-level BP term reflecting DHPR's indirect role in aromatic amino acid metabolism: by regenerating BH4 it supports the aromatic amino acid hydroxylases (notably phenylalanine hydroxylase). DHPR is not itself an amino-acid-metabolizing enzyme; it acts upstream by supplying the cofactor. Reason: The link to amino acid metabolism is real but indirect and the term is extremely broad. The informative, direct process terms are the BH4/ dihydrobiopterin metabolic terms. Retain as non-core rather than as a core function. Supporting Evidence: PMID:3033643 an essential component of the pterin-dependent aromatic amino acid hydroxylating systems |
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Download this section (compressed HTML)Q: Does the single high-throughput mitochondrial-proteome detection of QDPR reflect a genuine, functionally relevant mitochondrial pool, or co-purification of the abundant cytosolic enzyme?
Q: Which reduced nicotinamide cofactor (NADH vs NADPH) predominates in vivo for human DHPR-mediated BH4 regeneration, and does the preference differ between tissues (e.g. brain vs liver)?
Experiment: Steady-state and pre-steady-state kinetics of purified human DHPR comparing NADH vs NADPH as hydride donors with quinonoid dihydrobiopterin as substrate.
Hypothesis: Human DHPR regenerates BH4 using NADH as the primary physiological hydride donor, with NADPH as an alternative cofactor.
Type: enzyme kinetics
Experiment: Subcellular fractionation with DHPR activity assay, plus endogenous immunofluorescence/immuno-EM, to test for bona fide mitochondrial DHPR activity versus exclusively cytosolic localization.
Hypothesis: QDPR is exclusively cytosolic and the mitochondrial-proteome detection is a co-purification artifact rather than a functional mitochondrial pool.
Type: subcellular fractionation and imaging
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