title: N-lobe versus C-lobe complexation of bismuth by human transferrin.
abstract: Interactions of recombinant N-lobe of human serum transferrin (hTF/2N) with Bi3+, a metal ion widely used in medicine, have been investigated by both UV and NMR spectroscopy. The bicarbonate-independent stability constant for Bi3+ binding (K*) to hTF/2N was determined to be log K* 18.9+/-0.2 in 5 mM bicarbonate/10 mM Hepes buffer at 310 K, pH7.4. The presence of Fe3+ in the C-lobe of intact hTF perturbed Bi3+ binding to the N-lobe, whereas binding of Bi3+ to the C-lobe was unaffected by the presence of Fe3+ in the N-lobe. Reactions of Bi3+ (as bismuth nitrilotriacetate or ranitidine bismuth citrate) with hTF/2N in solutions containing 10 mM bicarbonate induced specific changes to high-field 1H-NMR peaks. The 1H co-ordination shifts induced by Bi3+ were similar to those induced by Fe3+ and Ga3+, suggesting that Bi3+ binding causes similar structural changes to those induced by hTF/2N. 13C-NMR data showed that carbonate binds to hTF/2N concomitantly with Bi3+.
authors.affiliation: Department of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, U.K.
authors.forename: H
authors.initials: H
authors.lastname: Sun
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: A B
authors.initials: AB
authors.lastname: Mason
authors.forename: R C
authors.initials: RC
authors.lastname: Woodworth
authors.forename: P J
authors.initials: PJ
authors.lastname: Sadler
mesh_terms: D001667:Binding, Competitive; D001729:Bismuth / Q000737:chemistry*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D011487:Protein Conformation; D014168:Transferrin / Q000737:chemistry*
chemical_list: D014168:Transferrin; D001729:Bismuth