Terbium(III) fluorescence probe studies on metal ion-binding sites in anticoagulation factor I from Agkistrodon
Xiaolong Xu1, Qingliang Liu, Yi Liu
1Department of Chemistry, University of Science and Technology of China, Hefei Anhui.
Abstract:
Anticoagulation factor I (ACF I) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X-binding protein with marked anticoagulant activity. Present studies show that holo-ACF I assumes a compactly folded structure in the range of pH 5-6, in which the most interior Trp residues and quenchers are adjacent. Tb3+ ions can completely replace both Ca2+ ions in holo-ACF I, as determined by equilibrium dialysis. Although the two Tb3+ ions in Tb3+-ACF I have slightly different luminescence efficiencies, both have similar quenching effects on the intrinsic fluorescence, suggesting that probably there are same numbers of Trp residues close to both Tb3+-binding sites. Two Tb3+-binding sites with similar apparent Tb3+ association constant values, (1.69 +/- 0.02) x 10(7) M(-1) and (1.42 +/- 0.01) x 10(7) M(-1), respectively, were further identified through Tb3+ fluorescence titration. In addition, it has been confirmed from the titration of holo-ACF I and Tb3+-ACF I with NBS that only interior Trp residues are involved in the energy transfer to Tb3+ ions and that all accessible Trp residues located in the surface of holo-ACF I have similar affinity to NBS, while those located in the surface of Tb3+-ACF I have two different kinds of affinity to NBS, which strongly suggests a conformational change of holo-ACF I upon substitution of Tb3+ for Ca2+. The results show that although the Tb3+-altered conformation of ACF I cannot support the binding of Tb3+-ACF I with FXa, determined by nondenaturing PAGE, Tb3+ ions are effective and useful fluorescence probes to analyze the structures and properties of Ca2+-binding sites in ACF I.
More Related Videos
12:52Iridium(III) Luminescent Probe for Detection of the Malarial Protein Biomarker Histidine Rich Protein-II
Published on: July 7, 2015
07:54Analysis of AtHIRD11 Intrinsic Disorder and Binding Towards Metal Ions by Capillary Gel Electrophoresis and Affinity Capillary Electrophoresis
Published on: August 22, 2018
Related Concept Videos
01:18Effects of EDTA on End-Point Detection Methods
In the visual method, metal-ion indicators (metallochromic dyes), which have distinct colors in their free and complex forms, are added to the mixture to signal the titration's end point. They form stable complexes with metal ions, but these complexes are weaker than the corresponding metal–EDTA complexes. As a result, EDTA...
01:26EDTA: Auxiliary Complexing Reagents
01:22EDTA: Chemistry and Properties
00:43Complexometric Titration: Ligands
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
02:42Valence Bond Theory