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Crystal structure of plantacyanin, a basic blue cupredoxin from spinach
O Einsle1, Z Mehrabian, R Nalbandyan
1Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Martinsried, Germany. einsle@biochem.mpg.de
Summary
The crystal structure of spinach basic blue protein (plantacyanin) was determined. A key lysine difference versus cucumber protein subtly alters copper site geometry, impacting redox potential.
Area of Science:
- Biochemistry
- Structural Biology
- Plant Science
Background:
- Plantacyanins are blue copper proteins involved in electron transport.
- Understanding their structure-function relationship is crucial for elucidating redox processes in plants.
Purpose of the Study:
- To determine the crystal structure of spinach basic blue protein (SBP).
- To compare the structure of SBP with cucumber basic blue protein (CBP) and understand differences in redox potential.
Main Methods:
- X-ray crystallography at 2.05 A resolution.
- Molecular replacement using CBP structure as a model.
- Structural comparison and analysis of copper ligand geometry.
Main Results:
- The three-dimensional structures of SBP and CBP are highly similar, with conserved hydrophobic cores.
- A single lysine residue in SBP replaces proline in CBP, causing subtle copper ligand distortion.
- Monomers of SBP showed variations in outer loop regions due to crystal packing, but not in functionally important areas.
Conclusions:
- The structural similarity between SBP and CBP suggests conserved function despite moderate sequence identity.
- The identified amino acid difference explains the observed redox potential variation.
- The protein structure does not impose significant conformational strain on the copper center in the oxidized state.