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The bacterial Sox (sulfur oxidizing) system allows the utilization of inorganic sulfur compounds in energy metabolism. Central to this process is the SoxYZ complex that carries the pathway intermediates on a cysteine residue near the C terminus of SoxY. Crystal structures have been determined for Paracoccus pantotrophus SoxYZ with the carrier cysteine in the underivatized state, conjugated to the polysulfide mimic beta-mercaptoethanol, and as the sulfonate adduct pathway intermediate. The carrier cysteine is located on a peptide swinging arm and is bracketed on either side by diglycine dipeptides acting as molecular universal joints. This structure provides a novel solution to the requirement that the cysteine-bound intermediates be able to access and orient themselves within the active sites of multiple partner enzymes. Adjacent to the swinging arm there is a conserved, deep, apolar pocket into which the beta-mercaptoethanol adduct extends. This pocket would be well suited to a role in protecting labile pathway intermediates from adventitious reactions.

Original publication




Journal article


J Biol Chem

Publication Date





23194 - 23204


Amino Acid Sequence, Bacterial Proteins, Crystallography, X-Ray, Cysteine, Mercaptoethanol, Models, Biological, Models, Molecular, Molecular Sequence Data, Oxidoreductases Acting on Sulfur Group Donors, Paracoccus pantotrophus, Peptides, Plasmids, Protein Conformation, Sequence Homology, Amino Acid, Sulfonic Acids, Sulfur