Mutations decouple proton transfer from phosphate cleavage in the dutpase catalytic reaction

Anna Lopata, Pablo G. Jambrina, Pankaz K. Sharma, Bernard R. Brooks, Judit Toth, Beata G. Vertessy, Edina Rosta

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Most enzymes present a catalytic mechanism where one or more proton transfer events occur coupled tightly together with the enzymatic chemical reaction. We show here that inactivating mutations decouple this proton transfer step from the phosphate cleavage reaction in dUTPase. Homotrimeric dUTPase enzymes catalyze the hydrolysis of dUTP to dUMP and pyrophosphate, using largely similar structural and functional groups as most AAA+ enzymes. dUTPases typically use a single Mg2+ ion as a cofactor in the active site that is formed by direct protein-protein contacts including all three protomers. Here we focus on the C-terminal arm structural motif, which has sequence and functional similarities to P-loop motifs and is required for catalysis. In this work, we have studied the functional roles of the C-terminal arm in ligand binding and catalysis by using QM/MM (quantum mechanics/molecular mechanics) calculations in conjunction with site-directed mutagenesis experiments. We also present a new method to assess the metal ion coordination symmetry during the catalytic reaction. Using this new implementation, we identified that the coordination symmetry follows a consistent pattern in the three systems studied, reaching the most symmetrical state near the transition states. We found that the phosphate cleavage proceeds with a concerted bimolecular (ANDN) mechanism with a loose dissociative transition state and that it is coupled with a proton transfer step involving a unanimously conserved Asp residue. We show that the main mechanistic effect of the lack of the C-terminal arm is to decouple the phosphate cleavage from the subsequent proton transfer step, resulting in a high-barrier altered reaction pathway.

Original languageEnglish
Pages (from-to)3225-3237
Number of pages13
JournalACS Catalysis
Volume5
Issue number6
DOIs
Publication statusPublished - Jun 5 2015

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Keywords

  • DFT (density functional theory)
  • QM/MM (quantum mechanics/molecular mechanics)
  • ab initio
  • continuous symmetry measure
  • coupled proton transfer
  • dUTPase
  • one-metal ion catalytic mechanism

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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