A new thermophilic nitrilase from Pyrococcus sp. M24D13

A new thermophilic nitrilase from an Antarctic hyperthermophilic microorganism by Geraldine V. Dennett and Jenny M. Blamey

Front. Bioeng. Biotechnol.  doi: 10.3389/fbioe.2016.00005

Several environmental samples from Antarctica were collected and enriched to search for microorganisms with nitrilase activity. A new thermostable nitrilase from a novel hyperthermophilic archaea Pyrococcus sp. M24D13 was purified and characterized. The activity of this enzyme increased as the temperatures rise from 70 up to 85 °C. Its optimal activity occurred at 85 °C and pH 7.5. This new enzyme shows a remarkable resistance to thermal inactivation retaining more than 50% of its activity even after 8 h of incubation at 85 °C. In addition, this nitrilase is highly versatile demonstrating activity towards different substrates such as benzonitrile (60 mM, aromatic nitrile) and butyronitrile (60 mM, aliphatic nitrile). Moreover the enzyme NitM24D13 also presents cyanidase activity.

Hyperthermophilic nitrile hydratases?

There are plenty of reports of nitrilases which have been cloned from organisms with names that denote obviously heat-loving tendencies- an example is the “Cloning, overexpression, and characterization of a thermoactive nitrilase from the hyperthermophilic archaeon Pyrococcus abyssi” by Mueller, Egorova, Vorgias, Boutou, Trauthwein, Verseck and Antranikian in Protein Expr Purif. 2006, 47(2), 672-81. It is quite noticeable that NHases do not appear to have the same hyperthermophilicity. If you search the translated genomes of the four organisms which produce nitrilases in this paper (Pyrococcus abyssi, Pyrococcus horikoshii, Pyrococcus furiosus, and Aeropyrum pernix) by using BLASTp against the alpha subunit of my favourite cobalt centred NHase CGA009 or the “local” iron centred NHase AJ270, you get just about nothing that shows any similarity.

Something that does stand out from examination of all the current PDB files of NHases that almost everyone says their NHase is thermostable or thermophilic. I get the impression that this labelling of these generally sensitive enzymes in itself tells a story.