1sur
From Proteopedia
|
PHOSPHO-ADENYLYL-SULFATE REDUCTASE
Overview
BACKGROUND: Assimilatory sulphate reduction supplies prototrophic, organisms with reduced sulphur for the biosynthesis of all, sulphur-containing metabolites. This process is driven by a sequence of, enzymatic steps involving phosphoadenylyl sulphate (PAPS) reductase., Thioredoxin is used as the electron donor for the reduction of PAPS to, phospho-adenosine-phosphate (PAP) and sulphite. Unlike most, electron-transfer reactions, there are no cofactors or prosthetic groups, involved in this reduction and PAPS reductase is one of the rare examples, of an enzyme that is able to store two electrons. Determination of the, structure of PAPS reductase is the first step towards elucidating the, biochemical details of the reduction of PAPS to sulphite. RESULTS: We have, determined the crystal structure of PAPS reductase at 2.0 A resolution in, the open, reduced form, in which a flexible loop covers the active site., The protein is active as a dimer, each monomer consisting of a central, six-stranded beta sheet with alpha helices packing against each side. A, highly modified version of the P loop, the fingerprint peptide of, mononucleotide-binding proteins, is present in the active site of the, protein, which appears to be a positively charged cleft containing a, number of conserved arginine and lysine residues. Although PAPS reductase, has no ATPase activity, it shows a striking similarity to the structure of, the ATP pyrophosphatase (ATP PPase) domain of GMP synthetase, indicating, that both enzyme families have evolved from a common ancestral, nucleotide-binding fold. CONCLUSIONS: The sequence conservation between, ATP sulphurylases, a subfamily of ATP PPases, and PAPS reductase and the, similarities in both their mechanisms and folds, suggest an evolutionary, link between the ATP PPases and PAPS reductases. Together with the N type, ATP PPases, PAPS reductases and ATP sulphurylases are proposed to form a, new family of homologous enzymes with adenine nucleotide alpha-hydrolase, activity. The open, reduced form of PAPS reductase is able to bind PAPS, whereas the closed oxidized form cannot. A movement between the two, monomers of the dimer may allow this switch in conformation to occur.
About this Structure
1SUR is a Single protein structure of sequence from Escherichia coli. Active as Phosphoadenylyl-sulfate reductase (thioredoxin), with EC number 1.8.4.8 Full crystallographic information is available from OCA.
Reference
Crystal structure of phosphoadenylyl sulphate (PAPS) reductase: a new family of adenine nucleotide alpha hydrolases., Savage H, Montoya G, Svensson C, Schwenn JD, Sinning I, Structure. 1997 Jul 15;5(7):895-906. PMID:9261082
Page seeded by OCA on Wed Nov 21 02:41:17 2007
