SsoPox is a lactonase endowed with promiscuous phosphotriesterase activity isolated from Sulfolobus solfataricus that belongs to the Phosphotriesterase- Like Lactonase family. Because of its intrinsic thermal stability, SsoPox is seen as an appealing candidate as a bioscavenger for organophosphorus compounds. A comprehensive kinetic characterisation of SsoPox has been performed with various phosphotriesters (insecticides) and phosphodiesters (nerve agent analogues) as substrates. We show that SsoPox is active for a broad range of OPs and remains active under denaturing conditions. In addition, its OP hydrolase activity is highly stimulated by anionic detergent at ambient temperature and exhibits catalytic efficiencies as high as k cat/K M of 10 5 M -1 s -1 against a nerve agent analogue. The structure of SsoPox bound to the phosphotriester fensulfothion reveals an unexpected and non-productive binding mode. This feature suggests that SsoPox's active site is sub-optimal for phosphotriester binding, which depends not only upon shape but also on localised charge of the ligand.
Bibliographical noteFunding Information:
We are grateful to Dr. Moshe Goldsmith for the kind gift of CMP-coumarin, IMP-coumarin and PinP-coumarin. We thank Professor Dan Tawfik for constructive discussions on the project and for hosting J.H. in its laboratory. We thank the AFMB laboratory (Marseille, France) for the access to protein production and crystallisation platforms. This work was granted by DGA, France (REI. 2009 34 0045). J.H. and G.G. are PhD students granted by DGA. M.E. is a fellow supported by the IEF Marie Curie program (grant No. 252836).
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