Abstract
Vanadium-binding proteins, or Vanabins, have recently been isolated from the vanadium-rich ascidian, Ascidia sydneiensis samea. Recent reports indicate that Vanabin2 binds twenty V(IV) ions at pH 7.5, and that it has a novel bow-shaped conformation. However, the role of Vanabin2 in vanadium accumulation by the ascidian has not yet been determined. In the present study, the effects of acidic pH on selective metal binding to Vanabin2 and on the secondary structure of Vanabin2 were examined. Vanabin2 selectively bound to V(IV), Fe(III), and Cu(II) ions under acidic conditions. In contrast, Co(II), Ni(II), and Zn(II) ions were bound at pH 6.5 but not at pH 4.5. Changes in pH had no detectable effect on the secondary structure of Vanabin2 under acidic conditions, as determined by circular dichroism spectroscopy, and little variation in the dissociation constant for V(IV) ions was observed in the pH range 4.5-7.5, suggesting that the binding state of the ligands is not affected by acidification. Taken together, these results suggest that the reason for metal ion dissociation upon acidification is attributable not to a change in secondary structure but, rather, that it is caused by protonation of the amino acid ligands that complex with V(IV) ions.
| Original language | English |
|---|---|
| Pages (from-to) | 1096-1101 |
| Number of pages | 6 |
| Journal | Biochimica et Biophysica Acta - General Subjects |
| Volume | 1760 |
| Issue number | 7 |
| DOIs | |
| Publication status | Published - 2006 Jul 1 |
| Externally published | Yes |
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Keywords
- Ascidian
- Copper
- Metal selectivity
- Metal-binding protein
- Vanadium
ASJC Scopus subject areas
- Biophysics
- Biochemistry
- Molecular Biology
Cite this
Selective metal binding by Vanabin2 from the vanadium-rich ascidian, Ascidia sydneiensis samea. / Kawakami, Norifumi; Ueki, Tatsuya; Matsuo, Koichi; Gekko, Kunihiko; Michibata, Hitoshi.
In: Biochimica et Biophysica Acta - General Subjects, Vol. 1760, No. 7, 01.07.2006, p. 1096-1101.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Selective metal binding by Vanabin2 from the vanadium-rich ascidian, Ascidia sydneiensis samea
AU - Kawakami, Norifumi
AU - Ueki, Tatsuya
AU - Matsuo, Koichi
AU - Gekko, Kunihiko
AU - Michibata, Hitoshi
PY - 2006/7/1
Y1 - 2006/7/1
N2 - Vanadium-binding proteins, or Vanabins, have recently been isolated from the vanadium-rich ascidian, Ascidia sydneiensis samea. Recent reports indicate that Vanabin2 binds twenty V(IV) ions at pH 7.5, and that it has a novel bow-shaped conformation. However, the role of Vanabin2 in vanadium accumulation by the ascidian has not yet been determined. In the present study, the effects of acidic pH on selective metal binding to Vanabin2 and on the secondary structure of Vanabin2 were examined. Vanabin2 selectively bound to V(IV), Fe(III), and Cu(II) ions under acidic conditions. In contrast, Co(II), Ni(II), and Zn(II) ions were bound at pH 6.5 but not at pH 4.5. Changes in pH had no detectable effect on the secondary structure of Vanabin2 under acidic conditions, as determined by circular dichroism spectroscopy, and little variation in the dissociation constant for V(IV) ions was observed in the pH range 4.5-7.5, suggesting that the binding state of the ligands is not affected by acidification. Taken together, these results suggest that the reason for metal ion dissociation upon acidification is attributable not to a change in secondary structure but, rather, that it is caused by protonation of the amino acid ligands that complex with V(IV) ions.
AB - Vanadium-binding proteins, or Vanabins, have recently been isolated from the vanadium-rich ascidian, Ascidia sydneiensis samea. Recent reports indicate that Vanabin2 binds twenty V(IV) ions at pH 7.5, and that it has a novel bow-shaped conformation. However, the role of Vanabin2 in vanadium accumulation by the ascidian has not yet been determined. In the present study, the effects of acidic pH on selective metal binding to Vanabin2 and on the secondary structure of Vanabin2 were examined. Vanabin2 selectively bound to V(IV), Fe(III), and Cu(II) ions under acidic conditions. In contrast, Co(II), Ni(II), and Zn(II) ions were bound at pH 6.5 but not at pH 4.5. Changes in pH had no detectable effect on the secondary structure of Vanabin2 under acidic conditions, as determined by circular dichroism spectroscopy, and little variation in the dissociation constant for V(IV) ions was observed in the pH range 4.5-7.5, suggesting that the binding state of the ligands is not affected by acidification. Taken together, these results suggest that the reason for metal ion dissociation upon acidification is attributable not to a change in secondary structure but, rather, that it is caused by protonation of the amino acid ligands that complex with V(IV) ions.
KW - Ascidian
KW - Copper
KW - Metal selectivity
KW - Metal-binding protein
KW - Vanadium
UR - http://www.scopus.com/inward/record.url?scp=33744980658&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33744980658&partnerID=8YFLogxK
U2 - 10.1016/j.bbagen.2006.03.013
DO - 10.1016/j.bbagen.2006.03.013
M3 - Article
C2 - 16631310
AN - SCOPUS:33744980658
VL - 1760
SP - 1096
EP - 1101
JO - Biochimica et Biophysica Acta - General Subjects
JF - Biochimica et Biophysica Acta - General Subjects
SN - 0006-3002
IS - 7
ER -