5dyh
Ti(IV) bound human serum transferrin
Structural highlights
DiseaseTRFE_HUMAN Defects in TF are the cause of atransferrinemia (ATRAF) [MIM:209300. Atransferrinemia is rare autosomal recessive disorder characterized by iron overload and hypochromic anemia.[1] [2] FunctionTRFE_HUMAN Transferrins are iron binding transport proteins which can bind two Fe(3+) ions in association with the binding of an anion, usually bicarbonate. It is responsible for the transport of iron from sites of absorption and heme degradation to those of storage and utilization. Serum transferrin may also have a further role in stimulating cell proliferation. Publication Abstract from PubMedHuman serum transferrin (sTf) is a protein that mediates the transport of iron from blood to cells. Assisted by the synergistic anion carbonate, sTf transports Fe(III) by binding the metal ion in a closed conformation. Previous studies suggest sTf's role as a potential transporter of other metals such as titanium. Ti is a widely used metal in colorants, foods, and implants. A substantial amount of Ti is leached into blood from these implants. However, the fate of the leached Ti and its transport into the cells is not known. Understanding Ti interaction with sTf assumes a greater significance with our ever increasing exposure to Ti in the form of implants. On the basis of in vitro studies, it was speculated that transferrin can bind Ti(IV) assisted by a synergistic anion. However, the role and identity of the synergistic anion(s) and the conformational state in which sTf binds Ti(IV) are not known. Here we have solved the first X-ray crystal structure of a Ti(IV)-bound sTf. We find that sTf binds Ti(IV) in an open conformation with both carbonate and citrate as synergistic anions at the metal binding sites, an unprecedented role for citrate. Studies with cell lines suggest that Ti(IV)-sTf is transported into cells and that sTf and citrate regulate the metal's blood speciation and attenuate its cytotoxic property. Our results provide the first glimpse into the citrate-transferrin synergism in the regulation of Ti(IV) bioactivity and offers insight into the future design of Ti(IV)-based anticancer drugs. Unusual Synergism of Transferrin and Citrate in the Regulation of Ti(IV) Speciation, Transport, and Toxicity.,Tinoco AD, Saxena M, Sharma S, Noinaj N, Delgado Y, Quinones Gonzalez EP, Conklin SE, Zambrana N, Loza-Rosas SA, Parks TB J Am Chem Soc. 2016 May 4;138(17):5659-65. doi: 10.1021/jacs.6b01966. Epub 2016, Apr 26. PMID:27070073[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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