3-Mercaptopropionate dioxygenase, a cysteine dioxygenase homologue, catalyzes the initial step of 3-Mercaptopropionate catabolism in the 3,3-Thiodipropionic acid-degrading bacterium variovorax paradoxus

Abstract

The thioether 3,3-thiodipropionic acid can be used as precursor substrate for biotechnological synthesis of 3-mercaptopro-pionic acid-containing polythioesters. Therefore, the hitherto unknown catabolism of this compound was elucidated to engineer novel and improved polythioester biosynthesis pathways in the future. Bacteria capable of using 3,3-thiodipropionic acid as the sole source of carbon and energy for growth were enriched from the environment. From eleven isolates, TBEA3, TBEA6, and SFWT were morphologically and physiologically characterized. Their 16 S rDNAs and other features affiliated these isolates to the β-subgroup of the proteobacteria. Tn5::mob mutagenesis of isolate Variovorax paradoxus TBEA6 yielded ten mutants fully or partially impaired in growth on 3,3-thio-dipropionic acid. Genotypic characterization of two 3,3-thio- dipropionic acid-negative mutants demonstrated the involvement of a bacterial cysteine dioxygenase (EC 1.13.11.22) homologue in the further catabolism ofthe 3,3-thiodipropionic acid cleavage product 3-mercaptopropionic acid. Detection of 3-sulfinopropionate in the supernatant ofone ofthese mutants during cultivation on 3,3-thiodipropionic acid as well as in vivo and in vitro enzyme assays using purified protein demonstrated oxygenation of 3-mercaptopropionic acid to 3-sulfinopropi-onate by this enzyme; cysteine and cysteamine were not used as substrate. Beside cysteine dioxygenase and cysteamine dioxygenase, this 3-mercaptopropionic acid dioxygenase is the third example for a thiol dioxygenase and the first report about the microbial catabolism of3-mercaptopropionic acid. Insertion of Tn5::mob in a gene putatively coding for a family III acyl-CoA-transferase resulted in the accumulation of 3-sulfinopropionate during cultivation on 3,3-thiodipropionic acid, indicating that this compound is further metabolized to 3-sulfinopropionyl-CoA and subsequently to propionyl-CoA. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.