{"uniprot":"Q2M296","gene":"MTHFSD","name":"Methenyltetrahydrofolate synthase domain-containing protein","organism":"Homo sapiens (Human)","status":"dark","length":383,"sequence":"MEPRAVGVSKQDIREQIWGYMESQNLADFPRPVHHRIPNFKGSYLACQNIKDLDVFARTQEVKVDPDKPLEGVRLLVLQSKKTLLVPTPRLRTGLFNKITPPPGATKDILRKCATSQGVRNYSVPIGLDSRVLVDLVVVGSVAVSEKGWRIGKGEGYADLEYAMMVSMGAVSKETPVVTIVHDCQVVDIPEELVEEHDITVDYILTPTRVIATGCKRPKPMGITWFKISLEMMEKIPILRSLRAREQQAGKDVTLQGEHQHLPEPGCQQTVPLSVGRRPPDTPGPETNSMEAAPGSPPGEGAPLAADVYVGNLPGDARVSDLKRALRELGSVPLRLTWQGPRRRAFLHYPDSAAAQQAVSCLQGLRLGTDTLRVALARQQRDK","function_summary":"A soluble human RNA-binding assembly that uses an N-terminal cyclo-ligase–like scaffold to organize a modification complex and a C-terminal RNA recognition motif to capture and orient tRNA substrates. By stabilizing multiprotein assemblies that act on structured RNA, it promotes site-specific tRNA modification and broader RNA-modification pathways. Its soluble architecture supports cytoplasmic function with episodic concentration in nuclear bodies where RNA maturation and quality control intersect.","plain_language":"MTHFSD has barely been studied. The model's best guess: A soluble human RNA-binding assembly that uses an N-terminal cyclo-ligase–like scaffold to organize a modification complex and a C-terminal RNA recognition motif to capture and orient tRNA substrates. By stabilizing multiprotein assemblies that act on structured RNA, it promotes site-specific tRNA modification and broader RNA-modification pathways.","uniprot_summary":"RNA-binding protein.","go_terms":{"molecular_function":[{"id":"GO:0003723","label":"RNA binding"}],"biological_process":[{"id":"GO:0009451","label":"RNA modification"},{"id":"GO:0006400","label":"tRNA modification"}],"cellular_component":[{"id":"GO:0005737","label":"cytoplasm"},{"id":"GO:0016604","label":"nuclear body"}]},"interpro":[{"id":"IPR037171","name":"NagB/RpiA transferase-like","type":"homologous_superfamily","start":9,"end":225},{"id":"IPR024185","name":"5-formyltetrahydrofolate cyclo-ligase-like domain superfamily","type":"homologous_superfamily","start":43,"end":218},{"id":"IPR012677","name":"Nucleotide-binding alpha-beta plait domain superfamily","type":"homologous_superfamily","start":298,"end":383},{"id":"IPR035979","name":"RNA-binding domain superfamily","type":"homologous_superfamily","start":308,"end":380},{"id":"IPR000504","name":"RNA recognition motif domain","type":"domain","start":306,"end":379},{"id":"IPR034359","name":"MTHFSD, RNA recognition motif","type":"domain","start":307,"end":378},{"id":"IPR002698","name":"5-formyltetrahydrofolate cyclo-ligase","type":"family","start":5,"end":269}],"reasoning":"I begin with the InterPro architecture. The N-terminal two-thirds of the protein are dominated by folate-enzyme–like folds: IPR037171 (NagB/RpiA transferase-like homologous superfamily, residues 9–225) and IPR024185 (5-formyltetrahydrofolate cyclo-ligase-like domain superfamily, residues 43–218) together with the family assignment IPR002698 (5-formyltetrahydrofolate cyclo-ligase family, residues 5–269). This trio establishes a cyclo-ligase scaffold that in many systems binds nucleotides and organizes catalytic loops, but in this protein it functions as a structural platform rather than an enzyme. The C-terminal third switches to nucleic-acid–binding modules: IPR012677 (nucleotide-binding alpha-beta plait domain superfamily, residues 298–383) provides a β-α-β sandwich that often supports RNA-binding surfaces; this is reinforced by IPR035979 (RNA-binding domain superfamily, residues 308–380) and a canonical IPR000504 RNA recognition motif (RRM) domain spanning residues 306–379, further specialized by IPR034359 (MTHFSD, RNA recognition motif, residues 307–378). The ordered layout—an N-terminal cyclo-ligase-like platform followed by a C-terminal RRM—creates a bipartite assembly: the N-terminus positions and stabilizes the complex, while the C-terminus confers direct RNA affinity and specificity.\n\nThis architecture causes RNA-binding molecular function. The RRM (IPR000504) and its superfamily signatures (IPR035979, IPR034359) directly mediate GO:0003723 RNA binding. The cyclo-ligase-like core (IPR002698; IPR037171; IPR024185) supplies a rigid, ligand-tunable scaffold that enhances RNA recognition indirectly by presenting and organizing RNA-contacting surfaces and by docking partner proteins.\n\nFrom this molecular function, the biological process follows. An RRM-bearing assembly that targets structured RNAs is primed to act in RNA modification pathways. The explicit coupling of an RNA-binding C-terminus to a non-catalytic folate-enzyme–like N-terminus is characteristic of tRNA-modification systems that assemble multiprotein machines. This supports GO:0009451 RNA modification and, more specifically, GO:0006400 tRNA modification. The mechanistic logic is that the RRM recruits and stabilizes tRNA substrates and accessory enzymes, enabling site-specific chemical alterations that tune translation.\n\nCellular location is inferred from where such assemblies operate. The soluble, non-membranous architecture and reliance on RNA-binding modules argue for a cytosolic environment, consistent with GO:0005737 cytoplasm. Many RNA-modification and surveillance assemblies transiently concentrate in nuclear bodies where RNA maturation and quality control intersect; the presence of modular RNA-binding domains and assembly scaffolds supports episodic residency in GO:0016604 nuclear body, providing access to both nascent and exported RNA pools.\n\nThese features suggest a mechanism: the N-terminal cyclo-ligase-like platform nucleates a tRNA-modification complex, while the C-terminal RRM captures and orients tRNA. The complex likely coordinates accessory enzymes that install site-specific modifications by recruiting and positioning catalytic partners on the structured tRNA scaffold. I hypothesize interactions with cytoplasmic tRNA-modification enzymes and RNA chaperones. Candidate partners include cytoplasmic tRNA methyltransferases and deacylase assemblies that commonly cohabit with RRM-containing scaffolds, as well as RNA-binding hubs that traffic between cytoplasm and nuclear bodies. Together, these interactions would stabilize a modular assembly that binds tRNA, aligns it for modification, and couples modification status to broader RNA-processing pathways.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q2M296.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q2M296"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q2M296/entry","atlas":"/p/Q2M296"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}