MFSD14B

Model summary

A lysosomal multi-pass membrane transporter that uses an alternating-access mechanism to move leucine and arginine across the lysosomal membrane, thereby tuning amino acid pools that feed into autophagy pathways. By coupling solute flux to the lysosomal environment and assembling with trafficking and autophagy machinery, it elevates cytosolic amino acid signals that positively regulate autophagic flux.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The core scaffold is unambiguously that of the Major Facilitator Superfamily: IPR036259 (MFS transporter superfamily, residues 41–454) overlays IPR020846 (Major facilitator superfamily domain, residues 44–454) and IPR011701 (Major facilitator superfamily, residues 49–394), defining a canonical 12-transmembrane, alternating-access transporter. Within this MFS framework, multiple TetA/MdtG-like signatures—IPR001958 (Tetracycline resistance protein TetA/multidrug resistance protein MdtG-like family, residues 82–101, 138–159, 168–190, 290–310, 343–363, 378–401)—mark conserved motifs associated with drug and metabolite transporters that often couple substrate flux to proton gradients. The presence of IPR005829 (Sugar transporter, conserved site, residues 100–116) further supports an MFS fold that uses a central cavity and rocker-switch mechanics rather than ATP hydrolysis. The ordered layout—broad MFS superfamily coverage flanked by TetA/MdtG-like elements—causes a secondary-active transmembrane transport mechanism that can accommodate small solutes and amino acids.

2. 02

   From this architecture, the molecular function resolves as a membrane transporter that binds other proteins during assembly and regulation.

   The MFS fold and TetA/MdtG-like motifs together support alternating-access transport and transient cytosolic loop interactions that enable assembly with trafficking and autophagy machinery. This justifies GO:0005515 protein binding as an intrinsic property of a multi-pass transporter that forms regulatory complexes.

3. 03

   The biological processes follow from the transported substrates and cellular context.

   The MFS scaffold is well-suited to move amino acids; here, the mechanistic inference aligns with GO:1903826 L-arginine transmembrane transport and GO:0015820 leucine transport. By mobilizing leucine and arginine across an intracellular membrane, the transporter supplies lysosome-proximal pools that tune cytosolic amino acid signaling. This amino-acid flux feeds forward into autophagy pathways: leucine signaling restrains initiation and promotes completion via mTORC1 and ATG pathways. Consequently, the transporter’s activity positively influences autophagic flux, matching GO:0010508 positive regulation of autophagy.

4. 04

   Cellular location is dictated by both the fold and targeting cues.

   A 12-TM MFS core implies a multi-pass membrane protein. The experimentally supported placement at the lysosomal membrane is consistent with the need to regulate luminal versus cytosolic amino acid pools; thus the cellular component is GO:0005765 lysosomal membrane. This localization explains how the transporter couples lysosomal metabolism to cytosolic autophagy control.

5. 05

   Mechanistically, I propose a proton-coupled alternating-access transporter that shuttles leucine and arginine between the lysosomal lumen and cytosol.

   By elevating cytosolic leucine/arginine availability, it modulates amino acid sensing pathways that feed into autophagy. The protein likely binds trafficking and autophagy factors through its cytosolic loops, coordinating with lysosomal membrane systems. Hypothesized interaction partners include lysosomal membrane glycoproteins and V-ATPase assemblies that establish proton gradients; adaptor complexes that target the transporter to lysosomes; and autophagy regulators that respond to leucine-dependent signaling. Together, these interactions position the transporter as a lysosomal gatekeeper for amino acid-dependent autophagic control.