The crystal structure of iron-free human serum transferrin provides insight into inter-lobe communication and receptor binding.
Serum transferrin reversibly binds iron in each of two lobes and delivers it to cells by a receptor-mediated, pH-dependent process. The binding and release of iron result in a large conformational change in which two subdomains in each lobe close or open with a rigid twisting motion around a hinge. We report the structure of human serum transferrin (hTF) lacking iron (apo-hTF), which was independently determined by two methods: 1) the crystal structure of recombinant non-glycosylated apo-hTF was solved at 2.7-A resolution using a multiple wavelength anomalous dispersion phasing strategy, by substituting the nine methionines in hTF with selenomethionine and 2) the structure of glycosylated apo-hTF (isolated from serum) was determined to a resolution of 2.7A by molecular replacement using the human apo-N-lobe and the rabbit holo-C1-subdomain as search models. These two crystal structures are essentially identical. They represent the first published model for full-length human transferrin and reveal that, in contrast to family members (human lactoferrin and hen ovotransferrin), both lobes are almost equally open: 59.4 degrees and 49.5 degrees rotations are required to open the N- and C-lobes, respectively (compared with closed pig TF). Availability of this structure is critical to a complete understanding of the metal binding properties of each lobe of hTF; the apo-hTF structure suggests that differences in the hinge regions of the N- and C-lobes may influence the rates of iron binding and release. In addition, we evaluate potential interactions between apo-hTF and the human transferrin receptor.
Wally
Jeremy
J
NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
Halbrooks
Peter J
PJ
Vonrhein
Clemens
C
Rould
Mark A
MA
Everse
Stephen J
SJ
Mason
Anne B
AB
Buchanan
Susan K
SK
D000595:Amino Acid Sequence; D001665:Binding Sites; D006801:Humans; D007501:Iron / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011990:Receptors, Transferrin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D014168:Transferrin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D011990:Receptors, Transferrin; D014168:Transferrin; D007501:Iron