SLC35G6

Model summary

A human multi-pass membrane transporter that assembles a tandem EamA translocation core to move small metabolites—particularly purine nucleobases—across cellular membranes. It folds and matures in the endoplasmic reticulum before functioning at the plasma membrane, where its oligomerization and adaptor contacts stabilize an alternating-access pathway for small-molecule flux. By shaping intracellular pools of purine nucleobases and related metabolites, it contributes to broader nucleotide and xenobiotic handling through a membrane-embedded transport mechanism.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   Two tandem EamA modules define the core: IPR000620 (EamA domain, residues 42–173) followed by IPR000620 (EamA domain, residues 192–324). EamA repeats are hallmark membrane-embedded transport modules that assemble a compact, multi-pass fold specialized for small-molecule translocation. This tandem arrangement is reinforced by two overlapping superfamily signatures—IPR037185 (Multidrug transporter EmrE superfamily, residues 77–176) and IPR037185 (Multidrug transporter EmrE superfamily, residues 230–326)—which together specify a drug/metabolite transporter scaffold rather than an enzyme. The ordered layout—EamA1 (42–173) then EamA2 (192–324), bracketed by EmrE-superfamily envelopes—creates a hydrophobic, multi-helical conduit that couples substrate binding to alternating-access transport. This architecture causes transmembrane movement of small aromatic and heterocyclic solutes and supports oligomerization-dependent function typical of small-molecule transporters.

2. 02

   From this scaffold, the molecular function resolves as a transporter that also engages in multivalent contacts.

   The EamA/EmrE framework lacks catalytic motifs but is optimized for substrate exchange and complex assembly; this justifies a primary function of protein binding (GO:0005515), reflecting oligomerization and adaptor interactions that stabilize the transport-competent state and tune substrate specificity.

3. 03

   The biological process follows from the chemistry handled by this fold.

   EamA/EmrE transporters frequently mediate nucleobase and drug flux. Here, the architecture and physiological role converge on purine handling: the transporter supports purine nucleobase transport (GO:0006863). By modulating intracellular pools of purines and purine-like metabolites, the protein can influence broader nucleotide and xenobiotic balance.

4. 04

   Cellular location is dictated by the membrane-embedded design and trafficking itinerary.

   The dual EamA core mandates a multi-pass topology, consistent with stable residence in intracellular and surface membranes. The presence of assembly and quality-control steps for polytopic proteins explains endoplasmic reticulum membrane localization (GO:0005789), while functional deployment at the cell surface accounts for plasma membrane localization (GO:0005886). This ER-to-plasma-membrane distribution is typical for transporters that fold in the ER and traffic forward.

5. 05

   Mechanistically, the tandem EamA units form a central translocation pathway that alternates access between cytosolic and luminal/extracellular sides.

   Substrate binding within the EmrE-superfamily cavity likely triggers conformational changes that expose and occlude the pathway, enabling vectorial movement of purine nucleobases and related small molecules. The transporter’s propensity for oligomerization and adaptor binding suggests it operates within larger assemblies. I therefore hypothesize interactions with ER assembly factors and trafficking machinery: in the ER it likely associates with chaperones and membrane biogenesis hubs to mature its multi-pass core; at the plasma membrane it may form complexes with other small-molecule transporters and purine-handling enzymes, coordinating nucleobase flux with cellular metabolic state.