The enzyme cysteine dioxygenase oxidises cysteine to its sulfinic acid at a ferrous iron active site and thus catalyses the first step in oxidative breakdown of cysteine. Due to its role in regulating cysteine levels it is linked to various diseases including cancer, rheumatoid arthritis and several neurological diseases, such as Alzheimer's and Parkinson's diseases. Here we report that through a BLAST search we have identified a gene expressing a bacterial form of the enzyme from Pseudomonas aeruginosa that shows reactivity for two different thiol substrates. Previously, thiol dioxygenases have been reported to be highly specific for a single substrate and we believe that this is the first reported case of such an enzyme recognising multiple substrates. We are investigating this intriguing promiscuity using a number of different kinetic and spectroscopic approaches. HPLC and NMR analyses show that the enzyme can not only utilize cysteine to produce cysteine sulfinic acid but also catalyses the conversion of 3-mercaptopropionic acid to 3-sulfinopropionic acid. Spectroscopic and HPLC determination of the kinetic parameters show comparable Km and kcat for both substrates (cysteine: Km=7.4 mM, kcat=1.3 min-1; 3-MPA: Km=0.98 mM, kcat=6.9 min-1) while a cysteine binding constant of Kd=1.3 mM has been estimated using M�ssbauer spectroscopy. However, other substrate homologs, specifically homocysteine and cysteamine, could not be utilized. This expanded but still very specific substrate profile of the bacterial homologue gives further insight into the function of cysteine dioxygenases in general and may lead to a better understanding of its mammalian counterpart.

Cysteine dioxygenase from <i>Pseudomonas aeruginosa</i> is a true thiol dioxygenase

246th National Meeting (2013)

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Cysteine dioxygenase from Pseudomonas aeruginosa is a true thiol dioxygenase