SLC22A14

Model summary

A multi-pass membrane carrier that uses a major facilitator fold to shuttle small metabolites across the mitochondrial inner membrane. It mediates cellular uptake of riboflavin and translocates endogenous and xenobiotic organic anions, including urate, thereby coupling mitochondrial flavin supply with broader purine and lipid mediator handling. By alternating access across its transmembrane core, it supports vitamin import for mitochondrial cofactor biogenesis and adjusts solute gradients that connect mitochondrial and cytosolic pathways.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   Three concordant signatures define a canonical major facilitator superfamily (MFS) transporter core: IPR020846 (Major facilitator superfamily domain, residues 119–563) sits centrally and is flanked and reinforced by IPR036259 (MFS transporter superfamily, homologous superfamily, residues 168–571) and IPR005828 (Major facilitator, sugar transporter-like family, residues 189–569). This layered arrangement—domain, superfamily, and family—covers roughly the middle two-thirds of the polypeptide and dictates a 12-transmembrane-helix fold that alternates access to shuttle small solutes across membranes. The MFS scaffold establishes a central, amphipathic cavity whose gating and coupling motifs drive secondary active transport. Such an architecture causes transmembrane transport of diverse metabolites and anions and typically requires transient protein–protein contacts for assembly and regulation, supporting both transporter activity and generic protein binding.

2. 02

   From this fold, the molecular function resolves as follows.

   The MFS core directly encodes GO:0032217 riboflavin transmembrane transporter activity, because the alternating-access cavity accommodates the isoalloxazine-containing vitamin and mediates its uptake. The same architecture supports GO:0008514 organic anion transmembrane transporter activity, explaining the capacity to move urate and other anionic metabolites. The broad interaction surfaces and assembly behavior of MFS carriers justify GO:0005515 protein binding, reflecting adaptor and scaffold contacts that tune trafficking and activity.

3. 03

   These activities map upward to biological processes.

   Translocation of urate through an MFS pore feeds into GO:0046415 urate metabolic process by governing cellular urate availability and flux. The transporter’s promiscuity toward endogenous and xenobiotic anions and monocarboxylates extends to GO:0015908 fatty acid transport and GO:0071715 icosanoid transport; the cavity’s hydrophobic gating can transiently accommodate long-chain acids and eicosanoids, coupling their membrane partitioning to vectorial movement. Together, these transport reactions constitute a versatile route-sharing system that balances purine catabolites and lipid mediators.

4. 04

   Cellular location follows from both the fold and physiological logic.

   A multi-pass MFS core predicts membrane embedding, and the experimentally supported placement at the mitochondrial inner membrane aligns with GO:0005743 mitochondrial inner membrane. Positioning at this barrier enables direct exchange between cytosol and the matrix, allowing riboflavin import for mitochondrial flavinylation and urate efflux/recruitment pathways that intersect with mitochondrial purine pools. The inner membrane setting also rationalizes how the carrier can influence cytosolic metabolite gradients indirectly via mitochondrial handling.

5. 05

   Mechanistically, I propose an alternating-access uniporter/antiporter that binds riboflavin and certain anions in a central cavity and cycles between inward- and outward-facing states.

   In mitochondria, this cycle prioritizes riboflavin uptake to sustain flavin cofactor biogenesis, while in other contexts it equilibrates urate and related solutes. The transporter likely forms transient complexes with inner-membrane assemblies that coordinate metabolite flow and regulate its itinerary.

6. 06

   These deductions suggest likely interaction partners.

   At the mitochondrial inner membrane, the carrier plausibly associates with the TIM/TOM import machinery and cristae-organizing scaffolds to stabilize its position and trafficking. It may also engage metabolic hubs that set local substrate gradients—such as the riboflavin kinase–FMN adenylyltransferase axis—and purine-handling systems that modulate urate availability. Such assemblies would tune transport efficiency and integrate the carrier into broader mitochondrial and cytosolic metabolic circuits.