FDXACB1

Model summary

A cytosolic aminoacylation factor that assembles a Class II aminoacylation platform to activate amino acids and support tRNA charging for protein synthesis. Its N-terminal RNA-handling module and C-terminal anticodon-binding domain cooperate with a central adenylation core to recognize tRNAs and execute aminoacylation chemistry. By organizing cytosolic translation machinery, it sustains lysine-linked pathways and likely tunes lysine availability to the ribosome through coordinated interactions with other aminoacylation and translational components.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture and its order along the polypeptide.

   The N-terminus (residues 7–175) carries IPR019446, a BMT5-like domain (25S rRNA uridine-N3 methyltransferase–like). Although derived from an rRNA methyltransferase fold, in cytosolic aminoacylation systems this kind of RNA/RNA-binding fold often repurposes as a structural platform for nucleotide- and RNA-associated chemistry rather than catalyzing methyl transfer. Immediately downstream, residues 289–521 belong to IPR045864, a Class II aminoacyl-tRNA synthetase/BPL/LPL homologous superfamily. This superfamily encodes the adenylation chemistry that activates amino acids and forms aminoacyl-adenylates; its presence is a decisive signal that the core of this protein executes ATP-dependent aminoacylation. The C-terminal third is dominated by IPR036690 (ferrodoxin-fold anticodon-binding domain superfamily, residues 526–624) and its specific instantiation IPR005121 (ferrodoxin-fold anticodon-binding domain, residues 530–624). This anticodon-binding module dictates tRNA identity-element recognition and positions the acceptor stem for acyl transfer. The linear arrangement—an N-terminal RNA-handling module, a central adenylation core, and a C-terminal anticodon-binding domain—creates a canonical Class II aminoacylation machine tuned for substrate selection and tRNA engagement.

2. 02

   This architecture causes a specific molecular function: it binds macromolecules to assemble a tRNA-charging complex.

   The ferrodoxin-fold anticodon-binding domain and the BMT5-like N-terminus provide multivalent RNA/protein interfaces, supporting GO:0005515 protein binding as a basal capability intrinsic to assembly and regulation of the aminoacylation apparatus. The Class II adenylation core further implies ATP-dependent activation of an amino acid and transfer to tRNA, which mechanistically underpins GO:0006418 tRNA aminoacylation for protein translation.

3. 03

   From this molecular function, the biological process follows directly.

   By forming an aminoacylation platform that recognizes and modifies tRNA-bound substrates, the enzyme drives GO:0043038 amino acid activation and culminates in GO:0006418 tRNA aminoacylation for protein translation. The explicit association with lysine biology is suggested by the enzyme’s role in generating lysyl-tRNA pools and its capacity to influence lysine availability to the ribosome.

4. 04

   Cellular localization is inferred from the soluble, multidomain architecture lacking transmembrane segments or targeting peptides and from the need to interface with cytosolic translation machinery.

   This places the protein in the cytosol, consistent with GO:0005829 cytosol and the broader cytoplasmic milieu where tRNA charging and ribosome-associated pathways operate.

5. 05

   Mechanistically, I hypothesize that the N-terminal BMT5-like domain stabilizes RNA or RNA–protein assemblies that chaperone substrate selection, while the central Class II adenylation core forms and resolves aminoacyl-adenylate intermediates.

   The C-terminal ferrodoxin-fold anticodon-binding domain confers tRNA identity recognition and positions the acceptor end for acyl transfer. Together, these modules create a cytosolic aminoacylation hub that not only charges tRNAs but also modulates lysine-linked translation outputs. Likely interaction partners include cytosolic lysine-tRNA synthetase assemblies and auxiliary aminoacylation factors that coordinate tRNA flux with ribosomes; transient contacts with ribosomal subunits and RNA-processing proteins would facilitate efficient handoff of aminoacylated tRNAs into the translational pathway.