Zinc/sulfur Single wavelength Anomalous Dispersion phasing of Zn-substituted pseudoazurin
What is it about?
In order to examine the phasing potential of the very weak anomalous signal of sulphur (Δf" 0,56 e-) and zinc (Δf" 0,68 e-) atoms using an in-house Cu-Kα radiation source, we substituted the native Cu2+ of pseudoazurin by Zn2+ ion and determined its crystal structure1 by Zn/S SAD phasing at 2.2 Å. To achieve this, Single wavelength Anomalous Dispersion (SAD) datasets have been initially collected with high multiplicity. The lowest, required multiplicity has also been investigated in order to obtain the minimal Zn/S substructure for structure determination.
Why is it important?
The sensitive detector along with the user-friendly data processing software provided very accurate and precise intensities that were sufficient even at unexpectedly low multiplicity (approx. 8-fold) to phase a protein structure employing the weak anomalous signal (Δf" about half an electron) of sulphur and zinc atoms on a home shield tube X-ray source.