title: Isolation and characterization of the iron-binding properties of a primitive monolobal transferrin from Ciona intestinalis.
abstract: Transferrins are bilobal glycoproteins responsible for iron binding, transport, and delivery in many higher organisms. The two homologous lobes of transferrins are thought to have evolved by gene duplication of an ancestral monolobal form. In the present study, a 37.7-kDa primitive monolobal transferrin (nicatransferrin, or nicaTf) from the serum of the model ascidian species Ciona intestinalis was isolated by using an immobilized iron-affinity column and characterized by using mass spectrometry and N-terminal sequencing. The protein binds one equivalent of iron(III) and exhibits an electron paramagnetic resonance spectrum that is anion-dependent. The UV/vis spectrum of nicaTf has a shoulder at 330 nm in both the iron-depleted and the iron-replete forms, but does not display the approximately 460 nm tyrosine-to-iron charge transfer band common to vertebrate serum transferrins under the conditions investigated. This result suggests that iron may adopt a different binding mode in nicaTf compared with the more highly evolved transferrin proteins. This difference in binding mode could have implications for the physiological role of the protein in the ascidian. The genome of C. intestinalis has genes for both a monolobal and a bilobal transferrin, and the sequences of both proteins are discussed in light of the known features of vertebrate serum transferrins as well as other transferrin homologs.
authors.affiliation: Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520-8107, USA.
authors.forename: Ritika
authors.initials: R
authors.lastname: Uppal
authors.forename: K V
authors.initials: KV
authors.lastname: Lakshmi
authors.forename: Ann M
authors.initials: AM
authors.lastname: Valentine
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002938:Ciona intestinalis / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005453:Fluorescence; D006801:Humans; D007501:Iron / Q000737:chemistry*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D012680:Sensitivity and Specificity; D016415:Sequence Alignment; D014168:Transferrin / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D014168:Transferrin; D007501:Iron