This domain is found in the sulfur oxidation protein SoxY. It is closely related to the Desulfoferrodoxin family Pfam:PF01880. Dissimilatory oxidation of thiosulfate is carried out by the ubiquitous sulfur-oxidizing (Sox) multi-enzyme system. In this system, SoxY plays a key role, functioning as the sulfur substrate-binding protein that offers its sulfur substrate, which is covalently bound to a conserved C-terminal cysteine, to another oxidizing Sox enzyme [1]. The structure of this domain shows an Ig-like fold [1].

1: X-ray crystallographic analysis of the sulfur carrier protein SoxY from Chlorobium limicola f. thiosulfatophilum reveals a tetrameric structure. Stout J, Van Driessche G, Savvides SN, Van Beeumen J; Protein Sci. 2007;16:589-601. PMID:17327392