Crystal structure of adenosine 5'-phosphosulfate kinase isolated from Archaeoglobus fulgidus.

The 3'-phosphoadenosine-5'-phosphosulfate (PAPS) molecule is essential during enzyme-catalyzed sulfation reactions as a sulfate donor and is an intermediate in the reduction of sulfate to sulfite in the sulfur assimilation pathway. PAPS is produced through a two-step reaction involving ATP sulfurylase and adenosine 5'-phosphosulfate (APS) kinase enzymes/domains. However, archaeal APS kinases have not yet been characterized and their mechanism of action remains unclear. Here, we first structurally characterized APS kinase from the hyperthermophilic archaeon Archaeoglobus fulgidus, (AfAPSK). We demonstrated the PAPS production activity of AfAPSK at the optimal growth temperature (83 °C). Furthermore, we determined the two crystal structures of AfAPSK: ADP complex and ATP analog adenylyl-imidodiphosphate (AMP-PNP)/Mg/APS complex. Structural and complementary mutational analyses revealed the catalytic and substrate recognition mechanisms of AfAPSK. This study also hints at the molecular basis behind the thermal stability of AfAPSK.