Phage-encoded dihydrofolate reductase (DHFR) that catalyzes the NADPH-dependent reduction of dihydrofolate (DHF) to tetrahydrofolate (THF). DfrP is an auxiliary metabolic gene (AMG) encoded by Bacillus phage phiNIT1, a Bastilleviridae phage. The phage carries both dfrP and thyA (thymidylate synthase) genes to form a self-sufficient thymidine synthesis cycle during infection. This ensures robust nucleotide production for viral DNA replication. DfrP belongs to the trimethoprim-resistant DfrA family of DHFRs, which can confer antibiotic resistance to the infected host cell.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004146 dihydrofolate reductase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Core enzymatic function. DfrP contains a conserved DHFR domain (IPR001796) and catalyzes the NADPH-dependent reduction of DHF to THF (EC 1.5.1.3). Well-supported by sequence homology and domain architecture. Supporting Evidence: file:9CAUD/dfrP/dfrP-deep-research-openai.md DfrP is a dihydrofolate reductase...catalyzes the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF) using NADPH as a cofactor |
| GO:0006730 one-carbon metabolic process | IEA GO_REF:0000043 | ACCEPT | Summary: DHFR activity is central to one-carbon metabolism by regenerating THF, which carries one-carbon units for nucleotide and amino acid biosynthesis. Appropriate annotation. Supporting Evidence: file:9CAUD/dfrP/dfrP-deep-research-openai.md the primary function of DfrP is to sustain the one-carbon folate cycle by regenerating THF |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000043 | REMOVE | Summary: True but too general. The more specific term GO:0004146 (dihydrofolate reductase activity) is already annotated and should be preferred. Reason: Redundant with GO:0004146 which provides the specific oxidoreductase activity. The general oxidoreductase term adds no additional information. |
| GO:0046452 dihydrofolate metabolic process | IEA GO_REF:0000118 | ACCEPT | Summary: Appropriate biological process annotation. DHFR directly metabolizes dihydrofolate by reducing it to tetrahydrofolate. Supporting Evidence: file:9CAUD/dfrP/dfrP-deep-research-openai.md DfrP catalyzes the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate |
| GO:0046654 tetrahydrofolate biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Core biological process. DfrP directly catalyzes the final step in THF biosynthesis - the reduction of 7,8-dihydrofolate to 5,6,7,8-tetrahydrofolate. This is not merely modulation of a host process; the phage-encoded enzyme directly performs the biosynthetic reaction. THF is essential for thymidylate synthesis (DNA precursor), purine synthesis, and amino acid biosynthesis. The phage carries this gene as an auxiliary metabolic gene to ensure robust THF production during viral DNA replication, forming a complete folate cycle together with its thymidylate synthase (thyA) gene. Supporting Evidence: file:9CAUD/dfrP/dfrP-deep-research-openai.md This reaction is essential for regenerating THF, the active form of folate, which is required for one-carbon transfer reactions in the cell file:9CAUD/dfrP/dfrP-deep-research-openai.md the reaction catalyzed by DfrP is needed to produce THF for the de novo synthesis of glycine and purines, and for the continuous production of DNA precursors like thymidine (via the thymidylate synthase pathway) file:9CAUD/dfrP/dfrP-deep-research-openai.md By providing its own DHFR and TS, phiNIT1 ensures that the infected host cell can efficiently produce dTMP and other nucleotides, even if host pathways are downregulated or if folate pools become limiting file:9CAUD/dfrP/dfrP-deep-research-openai.md The combined presence of TS and DHFR in phiNIT1 means the phage can form a complete folate cycle independent of host regulation, securing a robust supply of DNA building blocks for phage genome synthesis |
| GO:0046655 folic acid metabolic process | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: Appropriate broader process annotation. DHFR is a key enzyme in folate metabolism, converting oxidized folate (DHF) back to the reduced active form (THF). Reason: While correct, this is a broader parental process. The more specific GO:0046452 (dihydrofolate metabolic process) and GO:0046654 (tetrahydrofolate biosynthetic process) better capture the direct function. |
| GO:0050661 NADP binding | IEA GO_REF:0000120 | ACCEPT | Summary: DHFR uses NADPH as the electron donor/cofactor. The domain contains conserved NADP-binding motifs. Appropriate MF annotation. Supporting Evidence: file:9CAUD/dfrP/dfrP-deep-research-openai.md It binds the cofactor NADPH (evidenced by conserved NADP-binding motifs in DHFR enzymes) |
| GO:0030430 host cell cytoplasm | ISS GO_REF:0000120 | NEW | Summary: DfrP is predicted to localize to the host cell cytoplasm where folate metabolism occurs. As a viral enzyme expressed during phage infection, GO guidelines specify using 'host cell cytoplasm' (GO:0030430) rather than generic 'cytoplasm' for viral proteins. Cytoplasmic localization is expected by analogy to other DHFR enzymes (no signal peptide or transmembrane domains). Supporting Evidence: file:9CAUD/dfrP/dfrP-deep-research-openai.md the DfrP protein is expressed in the bacterial host's cytoplasm, which is the site of folate metabolism and nucleotide synthesis |
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