Apolactoferrin structure demonstrates ligand-induced conformational change in transferrins

Anderson, Bill; Baker, Heather M.; Norris, Gillian E.; Rumball, Sylvia V.; Baker, Edward N.

doi:10.1038/344784a0

Cited by 387 publications

(277 citation statements)

References 24 publications

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“…In fact the relative movement of domains CI and C2 is only 1.3 (Table 3). The possible structural and functional implications of this have been discussed elsewhere (Anderson, Baker, Norris, Rumball & Baker, 1990).…”

Section: Discussionmentioning

confidence: 99%

“…This suggests a mechanism for metal binding in which first the anion (CO 2-) and then the metal ion (Fe 3+ ) bind to one domain while the molecule is in this 'open' conformation, followed by a conformational change in which the cleft is closed, by domain rotation, to complete the metal-ion coordination (Anderson, Baker, Norris, Rumball & Baker, 1990). The least movement is seen in the C-terminal half of the molecule, in which the cleft is still closed, even though no metal is bound.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Molecular replacement solution of the structure of apolactoferrin, a protein displaying large-scale conformational change

Norris

Anderson²,

Baker³

1991

Acta Crystallogr Sect B

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The crystal structure of an orthorhombic form of human apolactoferrin (ApoLf) has been determined from 2.8 ~ diffractometer data by molecular replacement methods. A variety of search models derived from the diferric lactoferrin structure (Fe2Lf) were used to obtain a consistent solution to the rotation function. An R-factor search gave the correct translational solution and the model was refined by rigid-body least-squares refinement (program CORELS). Only three of the four domains were located correctly by this procedure, however; the fourth was finally placed correctly by rotating it manually onto three strands of electron density which were recognized as part of its central/3-sheet. The final model, refined by restrained least-squares methods to an R factor of 0.214 for data in the resolution range 10.0 to 2.8 A~, shows a large domain movement in the N-terminal half of the molecule (a 54 rotation of domain N2) and smaller domain movements elsewhere, when compared with Fe=Lf. A feature of the crystal structure is that although the ApoLf and Fe2Lf unit cells appear very similar, their crystal packing and molecular structures are quite different.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Molecular replacement solution of the structure of apolactoferrin, a protein displaying large-scale conformational change

Norris

Anderson²,

Baker³

1991

Acta Crystallogr Sect B

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“…For example, in the human apo-lactoferrin (LTF) structure the iron-binding cleft in the N-lobe opens 53.4°, whereas the C-lobe is closed (similar to the diferric structure but lacking iron) (47 , and Pro 247 due to the ϳ36°psi changes between the ferric and apo-forms of these residues. As expected from the close structural alignment of our N-lobe with the isolated apo N-lobe, we observe similar changes in the same residues when compared with the iron-containing pig TF N-lobe.…”

Section: Resultsmentioning

confidence: 99%

The Crystal Structure of Iron-free Human Serum Transferrin Provides Insight into Inter-lobe Communication and Receptor Binding

Wally

Halbrooks

Vonrhein

et al. 2006

Journal of Biological Chemistry

226

258

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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-Å 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 2.7 Å 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°and 49.5°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.The transferrins are a family of bilobal iron-binding proteins that play the crucial role of binding ferric iron and keeping it in solution, thereby controlling the levels of this important metal in the body (1, 2). Human serum transferrin (hTF) 4 is synthesized in the liver and secreted into the plasma; it acquires Fe(III) from the gut and delivers it to iron requiring cells by binding to specific transferrin receptors (TFR) on their surface. The entire hTF⅐TFR complex is taken up by receptor-mediated endocytosis culminating in iron release within the endosome (3). Essential to the re-utilization of hTF, iron-free hTF (apo-hTF) remains bound to the TFR at low pH. When the apo-hTF⅐TFR complex is returned to the cell surface, apo-hTF is released to acquire more iron.Strong homologies exist, both between TF family members, and between the two lobes of any given TF (4, 5). Each N-and C-lobe is divided into two subdomains (designated N1 and N2, and C1 and C2) connected by a hinge that gives rise to a deep cleft containing the iron-binding ligands. Iron is coordinated by four highly conserved amino acid residues: an aspartic acid (the sole ligand from the N1-or C1-subdomain), a tyrosine in the hinge at the edge of the N2-or C2-subdomain, a second tyrosine within the N2-or C2-subdomain, and a histidine at the hinge bordering the N1-or C1-subdomain. In addition, the iron atom is bound by two oxygen atoms from the synergistic anion (carbonate), w...

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“…2B). X-ray (Anderson et al, 1990) and other physical studies (Rosseneu-Motreff et al, 1971;Kilar & Simon, 1985) also show that conformational changes accompany iron binding and release. In vivo, such local conformational changes might be associated with the binding of Tf to the receptor at the cell surface and release of the bound irons.…”

Section: Discussionmentioning

confidence: 99%

Conformational stability of porcine serum transferrin

et al. 1992

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The conformation of porcine serum ferric transferrin (Tf) and its stability against denaturation were studied by circular dichroism. [33][34][35][36][37]. Removal of the bound ferric ions (apo-Tf) did not alter the overall conformation, but there were subtle changes in local conformation based on its near-UV CD spectrum. The Tfs were stable between pH 3.5 and 11. Denaturation by guanidine hydrochloride (Gu-HCI) showed two transitions at 1.6 and 3.4 M denaturant. The process of denaturation by acid and base was reversible, whereas that by Gu-HCI was partially reversible. The irreversible thermal unfolding of Tfs began at temperatures above 60 "C and was not complete even at 80 "C. The bound irons (based on absorbance at 460 nm) were completely released at pH <4 or in Gu-HCI solution above 1.7 M, when the protein began to unfold, but they remained intact in neutral solution even at 85 "C. The NH2-and COOH-terminal halves of the Tf molecule obtained by limited trypsin digestion had CD spectra similar to the spectrum of native Tf, and the COOH-terminal fragment had more stable secondary structure than the NH,-terminal fragment.

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Apolactoferrin structure demonstrates ligand-induced conformational change in transferrins

Cited by 387 publications

References 24 publications

Molecular replacement solution of the structure of apolactoferrin, a protein displaying large-scale conformational change

Molecular replacement solution of the structure of apolactoferrin, a protein displaying large-scale conformational change

The Crystal Structure of Iron-free Human Serum Transferrin Provides Insight into Inter-lobe Communication and Receptor Binding

Conformational stability of porcine serum transferrin

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