{"uniprot":"Q8MH63","gene":"SLC7A5P1","name":"Putative L-type amino acid transporter 1-like protein MLAS","organism":"Homo sapiens (Human)","status":"dark","length":180,"sequence":"MAGAGPKRRALAAPVAEEKEEAREKMLASKRADGAAPAGEGEGVTLQRNITLLNGVAIIVGAIIGSGIFVTPTGVLKEAGSPGLALVMWAACGVFSIVGALCYAELGTTISKSGGDYAYMLDVYGSLPAFLKLWIELLVIRPSSQYIVALVFATYLLKPLFPSCPVPEEAAKLMACHCVH","function_summary":"A human multi-pass membrane carrier that transports neutral amino acids—especially branched-chain species—across the cell surface. Its transmembrane core forms an alternating-access pathway that selectively binds and moves valine, leucine, isoleucine, and related neutral substrates such as methionine and phenylalanine, while excluding polar or acidic amino acids. Operating predominantly at the plasma membrane, it helps set intracellular amino acid pools that feed biosynthesis and signaling pathways. A minor nucleoplasm-associated pool is plausible through regulatory trafficking and signaling linkages.","plain_language":"SLC7A5P1 has barely been studied. The model's best guess: A human multi-pass membrane carrier that transports neutral amino acids—especially branched-chain species—across the cell surface. Its transmembrane core forms an alternating-access pathway that selectively binds and moves valine, leucine, isoleucine, and related neutral substrates such as methionine and phenylalanine, while excluding polar or acidic amino acids.","uniprot_summary":"Transporter for branched-chain amino acids such as valine, leucine and isoleucine. Also transports neutral amino acids such as methionine and phenylalanine, and to a lesser extent, polar and acidic amino acids. No transport of asparagine and glutamate.","go_terms":{"molecular_function":[{"id":"GO:0015179","label":"L-amino acid transmembrane transporter activity"},{"id":"GO:0015175","label":"neutral L-amino acid transmembrane transporter activity"},{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0015804","label":"neutral amino acid transport"}],"cellular_component":[{"id":"GO:0005886","label":"plasma membrane"},{"id":"GO:0005654","label":"nucleoplasm"}]},"interpro":[{"id":"IPR050598","name":"Cellular Amino Acid Transporter","type":"family","start":40,"end":179},{"id":"IPR002293","name":"Amino acid/polyamine transporter I","type":"family","start":51,"end":163}],"reasoning":"I begin with the InterPro architecture. The N-terminal half of the polypeptide carries IPR050598 (Cellular Amino Acid Transporter family) spanning residues 40–179, and nested within it sits IPR002293 (Amino acid/polyamine transporter I family) from residues 51–163. This tandem of two transporter-family signatures defines a classical APC (amino acid–polyamine–organocation) superfamily core that folds into a multi-pass membrane bundle. The overlap and order—AAP/I-family signatures embedded within a broader cellular amino acid transporter scaffold—establish a canonical alternating-access transporter core that forms a substrate pathway through the lipid bilayer. Such an arrangement dictates a solute-exchange mechanism rather than channel-like conduction, and it typically coordinates neutral amino acid recognition via a hydrophobic pocket suited to branched-chain side chains.\n\nThis transporter architecture causally specifies molecular function. The APC fold and its conserved transmembrane helices generate a gated pathway that catalyzes L-amino acid transmembrane transporter activity (GO:0015179). The substrate pocket chemistry and the AAP/I family bias toward neutral residues, supporting neutral L-amino acid transmembrane transporter activity (GO:0015175). The physicochemical tuning of the binding cavity explains selective transport of branched-chain amino acids—valine, leucine, isoleucine—and compatibility with methionine and phenylalanine, while excluding polar/acidic substrates such as glutamate or asparagine. The presence of broad interaction surfaces typical of polytopic transporters also supports auxiliary protein binding (GO:0005515), which is expected for assembly, trafficking, and regulation of multi-pass carriers.\n\nFrom function to process, a neutral amino acid transporter that preferentially handles branched-chain species directly drives neutral amino acid transport (GO:0015804). By supplying and balancing essential neutral amino acids, this transporter sustains cellular biosynthesis and signaling pathways that depend on leucine and related metabolites. The alternating-access cycle—likely proton-coupled or exchange-driven—enables concentrative uptake at physiological gradients, thereby shaping cytosolic amino acid pools.\n\nCellular location follows from the fold and mechanism. A multi-pass APC transporter is intrinsically membrane-embedded and is expected at the plasma membrane (GO:0005886), where it mediates uptake from the extracellular milieu. The same architecture is compatible with intracellular membranes, and the observed distribution of many AAP-family members supports cycling between surface and endomembrane compartments. A nucleoplasmic signal (GO:0005654) can be reconciled by a regulatory pool: some fraction of the protein or its regulatory fragments may transiently associate with nuclear compartments, potentially via trafficking or signaling routes that couple membrane transport status to nuclear functions. Thus, while the primary operational site is the cell surface, a nucleoplasmic-associated fraction is plausible and consistent with multi-pass transporter regulatory biology.\n\nMechanistically, I hypothesize a secondary-active transporter that uses alternating access to exchange neutral amino acids across the plasma membrane, favoring branched-chain substrates through a hydrophobic binding cavity. The transporter likely forms transient complexes with cytosolic adaptors and regulatory proteins that govern endocytosis and signaling. Candidate partners include amino acid–sensing and trafficking modules that tune surface abundance and activity: SLC38A9 and mTORC1 pathway components that respond to leucine availability; clathrin adaptor complexes (e.g., AP-2) and endocytic machinery that modulate plasma-membrane residency; and cytosolic scaffolds that bind polytopic carriers (consistent with the observed protein-binding capacity). Together, these interactions would coordinate amino acid uptake with growth and stress-responsive pathways.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q8MH63.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q8MH63"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q8MH63/entry","atlas":"/p/Q8MH63"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}