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Structure of viscotoxin A3: disulfide location from weak SAD data
Judit E Debreczeni1, Beatrix Girmann, Axel Zeeck
1Lehrstuhl für Strukturchemie, Georg-August Universität, Tammannstrasse 4, Göttingen, Germany.
Acta Crystallographica. Section D, Biological Crystallography
|December 4, 2003
Summary
The crystal structure of viscotoxin A3 (VT A3) from European mistletoe was determined. This protein, similar to thionins, features a unique L-shaped fold with associated phosphate anions.
Area of Science:
- Biochemistry
- Structural Biology
- X-ray Crystallography
Background:
- Viscotoxin A3 (VT A3) is a protein extracted from European mistletoe (Viscum album L.).
- Understanding the structure of VT A3 is crucial for elucidating its biological functions.
Purpose of the Study:
- To determine the high-resolution crystal structure of viscotoxin A3.
- To characterize the structural features and oligomeric state of VT A3.
Main Methods:
- X-ray diffraction using in-house Cu Kalpha radiation and synchrotron data.
- Structure solution utilizing anomalous diffraction of native sulfur atoms and the SHELXD program.
- Phase expansion and refinement using synchrotron data.
Main Results:
- The crystal structure of VT A3 was solved to 2.2 A resolution.
- VT A3 monomers (46 amino acids) exhibit an L-shaped fold, characteristic of alpha- and beta-thionins, with three disulfide bridges.
- The asymmetric unit contains two VT A3 monomers stabilized by hydrophobic interactions.
- Each monomer is associated with a phosphate anion, confirmed by 31P-NMR and MS.
Conclusions:
- The study provides the first detailed crystal structure of viscotoxin A3.
- The determined structure reveals structural similarities to thionins and identifies a novel phosphate association.
- This structural information lays the foundation for future functional studies of VT A3.