SAD at home: solving the structure of oxalate decarboxylase with the anomalous signal from manganese using X-ray data collected on a home source.

Oxalate decarboxylase (OxdC) from Bacillus subtilis is a hexamer containing two manganese ions per 43.6 kDa subunit. A single highly redundant data set collected at a medium resolution of 2 A on an in-house X-ray source was sufficient to solve the structure by the single-wavelength anomalous diffraction (SAD) method using the anomalous signal from the manganese ions. The experimentally phased electron-density map was of high quality, enabling 96% of the amino-acid sequence to be automatically traced using ARP/wARP. Further analysis showed that only half of the original raw data were required for successful structure solution. Manganese currently occurs in approximately 2% of PDB entries. A brief survey suggests that several of these structures could also have been determined using manganese SAD. Moreover, the ability of manganese to substitute for other more commonly occurring divalent metal ions may indicate that the use of Mn SAD could have much wider application.