Interaction between the peripheral site residues of human butyrylcholinesterase, D70 and Y332, in binding and hydrolysis of substrates

Patrick Masson, Weihua Xie, Marie Thérèse Froment, Vladislav Levitsky, Pierre Louis Fortier, Christine Albaret, Oksana Lockridge

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Abstract

Human butyrylcholinesterase displays substrate activation with positively charged butyrylthiocholine (BTC) as the substrate. Peripheral anionic site (PAS) residues D70 and Y332 appear to be involved in the initial binding of charged substrates and in activation control. To determine the contribution of PAS residues to binding and hydrolysis of quaternary substrates and activation control, the single mutants D70G/Y and Y332F/A/D and the double mutants Y332A/D70G and Y332D/D70Y were studied. Steady-state hydrolysis of the charged substrates, BTC and succinyldithiocholine, and the neutral ester o-nitrophenyl butyrate was measured. In addition, inhibition of wild-type and mutant enzymes by tetramethylammonium was investigated, at low concentrations of BTC. Single and double mutants of D70 and Y332 showed little or no substrate activation, suggesting that both residues were important for activation control. The effects of double mutations on D70 and Y332 were complex. Double-mutant cycle analysis provided evidence for interaction between these residues. The category of interaction (either synergistic, additive, partially additive or antagonistic) was found to depend on the nature of the substrate and on measured binding or kinetic parameters. This complexity reflects both the cross-talk between residues involved in the sequential formation of productive Michaelian complexes and the effect of peripheral site residues on catalysis. It is concluded that double mutations on the PAS induce a conformational change in the active site gorge of butyrylcholinesterase that can alter both substrate binding and enzyme acylation. Copyright (C) 1999 Elsevier Science B.V.

Original languageEnglish (US)
Pages (from-to)281-293
Number of pages13
JournalBiochimica et Biophysica Acta - Protein Structure and Molecular Enzymology
Volume1433
Issue number1-2
DOIs
StatePublished - Aug 17 1999

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Keywords

  • Butyrylcholinesterase
  • Double-mutant cycle
  • Peripheral anionic site
  • Substrate binding

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Biochemistry
  • Molecular Biology

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