MTHFSD

Model 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.

Predicted Gene Ontology terms

1. 01

   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.

2. 02

   This 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.

3. 03

   From 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.

4. 04

   Cellular 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.

5. 05

   These 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.