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Elucidation of the active conformation of the APS-kinase domain of human PAPS synthetase 1.

Abstract：

:Bifunctional human PAPS synthetase (PAPSS) catalyzes, in a two-step process, the formation of the activated sulfate carrier 3'-phosphoadenosine 5'-phosphosulfate (PAPS). The first reaction involves the formation of the 5'-adenosine phosphosulfate (APS) intermediate from ATP and inorganic sulfate. APS is then further phosphorylated on its 3'-hydroxyl group by an additional ATP molecule to generate PAPS. The former reaction is catalyzed by the ATP-sulfurylase domain and the latter by the APS-kinase domain. Here, we report the structure of the APS-kinase domain of PAPSS isoform 1 (PAPSS1) representing the Michaelis complex with the products ADP-Mg and PAPS. This structure provides a rare glimpse of the active conformation of an enzyme catalyzing phosphoryl transfer without resorting to substrate analogs, inactivating mutations, or catalytically non-competent conditions. Our structure shows the interactions involved in the binding of the magnesium ion and PAPS, thereby revealing residues critical for catalysis. The essential magnesium ion is observed bridging the phosphate groups of the products. This function of the metal ion is made possible by the DGDN-loop changing its conformation from that previously reported, and identifies these loop residues unambiguously as a Walker B motif. Furthermore, the second aspartate residue of this motif is the likely candidate for initiating nucleophilic attack on the ATP gamma-phosphate group by abstracting the proton from the 3'-hydroxyl group of the substrate APS. We report the structure of the APS-kinase domain of human PAPSS1 in complex with two APS molecules, demonstrating the ability of the ATP/ADP-binding site to bind APS. Both structures reveal extended N termini that approach the active site of the neighboring monomer. Together, these results significantly increase our understandings of how catalysis is achieved by APS-kinase.

journal_name

J Mol Biol

journal_title

Journal of molecular biology

authors

Sekulic N,Dietrich K,Paarmann I,Ort S,Konrad M,Lavie A

doi

10.1016/j.jmb.2007.01.025

subject

Has Abstract

pub_date

2007-03-23 00:00:00

pages

488-500

issue

eissn

0022-2836

issn

1089-8638

pii

S0022-2836(07)00052-6

journal_volume

367

pub_type

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Elucidation of the active conformation of the APS-kinase domain of human PAPS synthetase 1.