Highest paraoxonase turnover rate found in a bacterial phosphotriesterase variant

). The PTE-SS0.2 was selectedfrom a library of binding-site mutants using a novelscreening method that combines partial lysis of bacterialcolonies and fluorogenic probes.Keywords: paraoxon/phosphotriesterase/screening/turnoverPseudomonas diminuta phosphotriesterase (PTE) catalysesthe hydrolysis of the man-made pesticide paraoxon with adiffusion-limited catalytic efficiency and a turn-over numbercomparable to that of the triosephosphate isomerase againstglyceraldehyde 3-phosphate in the ancient pathway of gly-colysis (Dumas et al., 1989; Putman et al., 1972). It is likelythat PTE has recently evolved from a lactonase ancestor withlow promiscuous PTE activity (Afriat et al., 2006). PTE andseveral of its naturally occurring homologues have been usedas templates to create laboratory-made mutants that exhibit awide range of turnover levels against paraoxon (Yang et al.,2003; Hawwa et al., 2009; Jackson et al., 2009; Xiang et al.,2009). Several of these mutants have been recently used tostudy the contribution of conformational changes to catalysis(Jackson et al., 2009). The present communication describesthe identification and characterisation of several PTE mutantswith distinct kinetic properties against paraoxon, in particularmutant SS0.2 (I106T/F132V/S308A/Y309W), which exhibitsthe highest reported in vitro paraoxonase turnover number(k