InterPro domain: IPR002500

This domain is found in phosphoadenosine phosphosulphate (PAPS) reductaseenzymes or PAPS sulphotransferase. PAPS reductase is part of the adenine nucleotide alpha hydrolases superfamily also including N type ATP PPasesand ATP sulphurylases [ 1 ].

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 [ 2 ].

The enzyme uses thioredoxin as an electron donor for the reduction of PAPS to phospho-adenosine-phosphate (PAP) [ 2 , 2 ].It is also found in NodP nodulation protein P from Rhizobium meliloti (Sinorhizobium meliloti) which has ATPsulphurylase activity (sulphate adenylate transferase) [ 3 ].

1. Crystal structure of phosphoadenylyl sulphate (PAPS) reductase: a new family of adenine nucleotide alpha hydrolases. Structure 5, 895-906
2. Reaction mechanism of thioredoxin: 3'-phospho-adenylylsulfate reductase investigated by site-directed mutagenesis. Eur. J. Biochem. 233, 347-56
3. ATP sulphurylase activity of the nodP and nodQ gene products of Rhizobium meliloti. Nature 348, 644-7