Catalytic and anticatalytic snapshots of a short-form ATP phosphoribosyltransferase

Magnus Stephen Alphey, Gemma Fisher, Ying Ge, Eoin Rory Gould, Teresa Filipa Guerreiro Machado, Huanting Liu, Gordon John Florence, James Henderson Naismith, Rafael G da Silva

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)
5 Downloads (Pure)

Abstract

Allosteric modulation of catalysis is a common regulatory strategy of flux-controlling biosynthetic enzymes. The enzyme ATP phosphoribosyltransferase (ATPPRT) catalyzes the first reaction in histidine biosynthesis, the magnesium-dependent condensation of ATP and 5-phospho-α-d-ribosyl-1-pyrophosphate (PRPP) to generate N1-(5-phospho-β-d-ribosyl)-ATP (PRATP) and pyrophosphate (PPi). ATPPRT is allosterically inhibited by the final product of the pathway, histidine. Hetero-octameric ATPPRT consists of four catalytic subunits (HisGS) and four regulatory subunits (HisZ) engaged in intricate catalytic regulation. HisZ enhances HisGS catalysis in the absence of histidine while mediating allosteric inhibition in its presence. Here we report HisGS structures for the apoenzyme and complexes with substrates (PRPP, PRPP-ATP, PRPP-ADP), product (PRATP), and inhibitor (AMP), along with ATPPRT holoenzyme structures in complexes with substrates (PRPP, PRPP-ATP, PRPP-ADP) and product (PRATP). These 10 crystal structures provide an atomic view of the catalytic cycle and allosteric activation of Psychrobacter arcticus ATPPRT. In both ternary complexes with PRPP-ATP, the adenine ring is found in an anticatalytic orientation, rotated 180° from the catalytic rotamer. Arg32 interacts with phosphate groups of ATP and PRPP, bringing the substrates in proximity for catalysis. The negative charge repulsion is further attenuated by a magnesium ion sandwiched between the α- and β-phosphate groups of both substrates. HisZ binding to form the hetero-octamer brings HisGS subunits closer together in a tighter dimer in the Michaelis complex, which poises Arg56 from the adjacent HisGS molecule for cross-subunit stabilization of the PPi leaving group at the transition state. The more electrostatically preorganized active site of the holoenzyme likely minimizes the reorganization energy required to accommodate the transition state. This provides a structural basis for allosteric activation in which chemistry is accelerated by facilitating leaving group departure.
Original languageEnglish
Pages (from-to)5601-5610
Number of pages10
JournalACS Catalysis
Volume8
Issue number6
Early online date11 May 2018
DOIs
Publication statusPublished - 1 Jun 2018

Keywords

  • Allostery
  • ATP phosphoribosyltransferase
  • Catalytic activation
  • HisG
  • Histidine
  • Biosynthesis
  • HisZ
  • Psychrophilic

Fingerprint

Dive into the research topics of 'Catalytic and anticatalytic snapshots of a short-form ATP phosphoribosyltransferase'. Together they form a unique fingerprint.

Cite this