TF (serotransferrin) notes

Deep research providers unavailable (no API keys). Notes from UniProt P02787 and cached literature.

Identity / localization

• Serotransferrin: secreted plasma glycoprotein made by the liver. Signal peptide 1-19, mature chain 20-698,
  bilobed structure (N-lobe 25-347, C-lobe 361-683), each lobe binds one Fe(3+) with bicarbonate.
• [UniProt P02787 "SUBCELLULAR LOCATION: Secreted"]; [UniProt "Expressed by the liver and secreted in plasma"].
• It is NOT an intrinsic membrane protein. During the transferrin cycle, holo-transferrin bound to its receptor
  (TfR1/TFRC) is internalized through clathrin-coated pits into early/recycling endosomes, where acidic pH
  releases Fe(3+); apo-transferrin recycles to the surface and is released. So endosomal, clathrin-coated-pit
  and cell-surface localizations are all receptor-bound pools of a soluble ligand.
• Localization conclusion: extracellular (blood plasma), secreted; cycles through cell-surface receptor,
  clathrin-coated pits and early/recycling endosomes bound to TfR; not membrane-anchored itself.

Function

• [UniProt "Transferrins are iron binding transport proteins which can bind two Fe(3+) ions"]; responsible for
  transport of iron to sites of storage and utilization; binds transferrin receptors TfR1/TfR2.
• Forms an iron-release complex with ferroportin (SLC40A1) and hephaestin (HEPH) PMID:37277838.
• Nutritional immunity: sequesters iron from pathogens; Neisseria pirate TF-bound iron via TbpA/TbpB
  [PMID:22327295, PMID:22343719].