title: 3'-Phosphoadenosine-5'-phosphosulfate reductase in complex with thioredoxin: a structural snapshot in the catalytic cycle.
abstract: The crystal structure of Escherichia coli 3'-phosphoadenosine-5'-phosphosulfate (PAPS) reductase in complex with E. coli thioredoxin 1 (Trx1) has been determined to 3.0 A resolution. The two proteins are covalently linked via a mixed disulfide that forms during nucleophilic attack of Trx's N-terminal cysteine on the Sgamma atom of the PAPS reductase S-sulfocysteine (E-Cys-Sgamma-SO3-), a central intermediate in the catalytic cycle. For the first time in a crystal structure, residues 235-244 in the PAPS reductase C-terminus are observed, depicting an array of interprotein salt bridges between Trx and the strictly conserved glutathione-like sequence, Glu238Cys239Gly240Leu241His242. The structure also reveals a Trx-binding surface adjacent to the active site cleft and regions of PAPS reductase associated with conformational change. Interaction at this site strategically positions Trx to bind the S-sulfated C-terminus and addresses the mechanism for requisite structural rearrangement of this domain. An apparent sulfite-binding pocket at the protein-protein interface explicitly orients the S-sulfocysteine Sgamma atom for nucleophilic attack in a subsequent step. Taken together, the structure of PAPS reductase in complex with Trx highlights the large structural rearrangement required to accomplish sulfonucleotide reduction and suggests a role for Trx in catalysis beyond the paradigm of disulfide reduction.
authors.affiliation: Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Chartron
authors.forename: Carrie
authors.initials: C
authors.lastname: Shiau
authors.forename: C David
authors.initials: CD
authors.lastname: Stout
authors.forename: Kate S
authors.initials: KS
authors.lastname: Carroll
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology; D008958:Models, Molecular; D010088:Oxidoreductases / Q000737:chemistry*; D013879:Thioredoxins / Q000737:chemistry*
chemical_list: D013879:Thioredoxins; D010088:Oxidoreductases; C052449:3'-phosphoadenylyl-5'-phosphosulfate reductase