Transferrin

4X1D, 1A8E, 1A8F, 1B3E, 1BP5, 1BTJ, 1D3K, 1D4N, 1DTG, 1FQE, 1FQF, 1JQF, 1N7W, 1N7X, 1N84, 1OQG, 1OQH, 1RYO, 1SUV, 2HAU, 2HAV, 2O7U, 2O84, 3FGS, 3QYT, 3S9L, 3S9M, 3S9N, 3SKP, 3V83, 3V89, 3V8X, 3VE1, 4H0W, 4X1B, 5DYH701822041ENSG00000091513ENSMUSG00000032554P02787Q921I1NM_001063NM_001354704NM_001354703NM_133977NP_001054NP_001341633NP_001341632NP_598738Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron (Fe) in biological fluids. Human transferrin is encoded by the TF gene.Transferrin bound to its receptor.Transferrin receptor complex.1a8e: HUMAN SERUM TRANSFERRIN, RECOMBINANT N-TERMINAL LOBE1a8f: HUMAN SERUM TRANSFERRIN, RECOMBINANT N-TERMINAL LOBE1b3e: HUMAN SERUM TRANSFERRIN, N-TERMINAL LOBE, EXPRESSED IN PICHIA PASTORIS1bp5: HUMAN SERUM TRANSFERRIN, RECOMBINANT N-TERMINAL LOBE, APO FORM1btj: HUMAN SERUM TRANSFERRIN, RECOMBINANT N-TERMINAL LOBE, APO FORM, CRYSTAL FORM 21d3k: HUMAN SERUM TRANSFERRIN1d4n: HUMAN SERUM TRANSFERRIN1dtg: HUMAN TRANSFERRIN N-LOBE MUTANT H249E1fqe: CRYSTAL STRUCTURES OF MUTANT (K206A) THAT ABOLISH THE DILYSINE INTERACTION IN THE N-LOBE OF HUMAN TRANSFERRIN1fqf: CRYSTAL STRUCTURES OF MUTANT (K296A) THAT ABOLISH THE DILYSINE INTERACTION IN THE N-LOBE OF HUMAN TRANSFERRIN1jqf: Human Transferrin N-Lobe Mutant H249Q1n7w: Crystal Structure of Human Serum Transferrin, N-Lobe L66W mutant1n7x: HUMAN SERUM TRANSFERRIN, N-LOBE Y45E MUTANT1n84: HUMAN SERUM TRANSFERRIN, N-LOBE1oqg: Crystal structure of the D63E mutant of the N-lobe human transferrin1oqh: Crystal Structure of the R124A mutant of the N-lobe human transferrin1ryo: Human serum transferrin, N-lobe bound with oxalate1suv: Structure of Human Transferrin Receptor-Transferrin Complex2hau: Apo-Human Serum Transferrin (Non-Glycosylated)2hav: Apo-Human Serum Transferrin (Glycosylated)2o7u: Crystal structure of K206E/K296E mutant of the N-terminal half molecule of human transferrin2o84: Crystal structure of K206E mutant of N-lobe human transferrin Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron (Fe) in biological fluids. Human transferrin is encoded by the TF gene. Transferrin glycoproteins bind iron tightly, but reversibly. Although iron bound to transferrin is less than 0.1% (4 mg) of total body iron, it forms the most vital iron pool with the highest rate of turnover (25 mg/24 h). Transferrin has a molecular weight of around 80 kDa and contains two specific high-affinity Fe(III) binding sites. The affinity of transferrin for Fe(III) is extremely high (association constant is 1020 M−1 at pH 7.4) but decreases progressively with decreasing pH below neutrality. When not bound to iron, transferrin is known as 'apotransferrin' (see also apoprotein). When a transferrin protein loaded with iron encounters a transferrin receptor on the surface of a cell, e.g., erythroid precursors in the bone marrow, it binds to it and is transported into the cell in a vesicle by receptor-mediated endocytosis. The pH of the vesicle is reduced by hydrogen ion pumps (H+ ATPases) to about 5.5, causing transferrin to release its iron ions. The receptor with its ligand bound transferrin is then transported through the endocytic cycle back to the cell surface, ready for another round of iron uptake.Each transferrin molecule has the ability to carry two iron ions in the ferric form (Fe3+). The gene coding for transferrin in humans is located in chromosome band 3q21. Medical professionals may check serum transferrin level in iron deficiency and in iron overload disorders such as hemochromatosis. In humans, transferrin consists of a polypeptide chain containing 679 amino acids and two carbohydrate chains. The protein is composed of alpha helices and beta sheets that form two domains. The N- and C- terminal sequences are represented by globular lobes and between the two lobes is an iron-binding site. The amino acids which bind the iron ion to the transferrin are identical for both lobes; two tyrosines, one histidine, and one aspartic acid. For the iron ion to bind, an anion is required, preferably carbonate (CO2−3). Transferrin also has a transferrin iron-bound receptor; it is a disulfide-linked homodimer. In humans, each monomer consists of 760 amino acids. It enables ligand bonding to the transferrin, as each monomer can bind to one or two atoms of iron. Each monomer consists of three domains: the protease, the helical, and the apical domains. The shape of a transferrin receptor resembles a butterfly based on the intersection of three clearly shaped domains.