title: X-ray structures of transferrins and related proteins.
abstract: BACKGROUND
  Transferrins are a group of iron-binding proteins including serum transferrin, lactoferrin and ovotransferrin.
  
  
  METHODS
  The structures of transferrins are discussed.
  
  
  CONCLUSIONS
  The typical transferrin molecules are folded into two homologous lobes. X-ray crystallography revealed that each lobe is further divided into two similarly sized domains, and that an iron-binding site is contained within the inter-domain cleft. The six iron coordination sites are occupied by four residues and a bidentate carbonate anion.
  
  
  CONCLUSIONS
  The structures of the apo- and holo-forms revealed that the transferrins undergo a large-scale conformational change upon the uptake and release of irons: domains rotate as rigid bodies around a screw axis passing through inter-domain contacts. The iron-release mechanism of transferrin N-lobe is also revealed by X-ray crystallography; two basic residues in two domains form an unusual hydrogen bond in neutral pH, and the bond should be broken and facilitate iron release at a low pH of the endosome. For ovotransferrin, the iron release kinetics of two lobes correspond well with the numbers of anion binding sites found in crystal structures. The structures of transferrins bound to other metals revealed that the flexibility of the transferrin structure allows the ability to bind to other metals. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.
authors.affiliation: Laboratory of Applied Structural Biology, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Uji, Kyoto 611-0011, Japan. kmizutani@kais.kyoto-u.ac.jp
authors.forename: Kimihiko
authors.initials: K
authors.lastname: Mizutani
authors.forename: Mayuko
authors.initials: M
authors.lastname: Toyoda
authors.forename: Bunzo
authors.initials: B
authors.lastname: Mikami
mesh_terms: D000818:Animals; D001665:Binding Sites; D003207:Conalbumin / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006801:Humans; D007501:Iron / Q000378:metabolism*; D007781:Lactoferrin / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D014168:Transferrin / Q000737:chemistry*
chemical_list: D014168:Transferrin; D003207:Conalbumin; D007501:Iron; D007781:Lactoferrin