2NNC

Structure of the sulfur carrier protein SoxY from Chlorobium limicola f thiosulfatophilum

Summary for 2NNC

• Entry DOI: 10.2210/pdb2nnc/pdb
• Related: 2NNF
• Descriptor: Sulfur covalently-binding protein, CHLORIDE ION, PHOSPHATE ION, ... (5 entities in total)
• Functional Keywords: sulfur binding protein, soxy, beta sandwich, green sulfur bacterium, ligand binding protein
• Biological source: Chlorobium limicola
• Total number of polymer chains: 2
• Total formula weight: 26324.79

Authors

Stout, J.,Van Driessche, G.,Savvides, S.N.,Van Beeumen, J. (deposition date: 2006-10-24, release date: 2007-03-13, Last modification date: 2023-12-27)

Primary citation

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

PubMed Abstract: Dissimilatory oxidation of thiosulfate in the green sulfur bacterium Chlorobium limicola f. thiosulfatophilum 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. Here, we report the crystal structures of a stand-alone SoxY protein of C. limicola f. thiosulfatophilum, solved at 2.15 A and 2.40 A resolution using X-ray diffraction data collected at 100 K and room temperature, respectively. The structure reveals a monomeric Ig-like protein, with an N-terminal alpha-helix, that oligomerizes into a tetramer via conserved contact regions between the monomers. The tetramer can be described as a dimer of dimers that exhibits one large hydrophobic contact region in each dimer and two small hydrophilic interface patches in the tetramer. At the tetramer interface patch, two conserved redox-active C-terminal cysteines form an intersubunit disulfide bridge. Intriguingly, SoxY exhibits a dimer/tetramer equilibrium that is dependent on the redox state of the cysteines and on the type of sulfur substrate component bound to them. Taken together, the dimer/tetramer equilibrium, the specific interactions between the subunits in the tetramer, and the significant conservation level of the interfaces strongly indicate that these SoxY oligomers are biologically relevant.

PubMed: 17327392
DOI: 10.1110/ps.062633607

Experimental method

X-RAY DIFFRACTION (2.14 Å)