Crystallization, preliminary crystallographic analysis and phasing of the thiosulfate-binding protein SoxY from Chlorobium limicola f. thiosulfatophilum.

The 22 kDa SoxYZ protein complex from the green sulfur bacterium Chlorobium limicola f. thiosulfatophilum is a central player in the sulfur-oxidizing (Sox) enzyme system of the organism by activating thiosulfate for oxidation by SoxXA and SoxB. It has been proposed that SoxYZ exists as a heterodimer or heterotetramer, but the properties and role of the individual components of the complex thus far remain unknown. Here, the heterologous expression, purification, and the crystallization of stable tetrameric SoxY are reported. Crystals of SoxY diffract to 2.15 A resolution and belong to space group C222(1), with unit-cell parameters a = 41.22, b = 120.11, c = 95.30 A. MIRAS data from Pt(2+)- and Hg(2+)-derivatized SoxY crystals resulted in an interpretable electron-density map at 3 A resolution after density modification.