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Journal of Bacteriology, October 2009, p. 6052-6058, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.00678-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Homotaurine Metabolized to 3-Sulfopropanoate in Cupriavidus necator H16: Enzymes and Genes in a Patchwork Pathway{triangledown} ,{dagger}

Jutta Mayer and Alasdair M. Cook*

Konstanz Research School of Chemical Biology, The University, D-78457 Konstanz, Germany

Received 25 May 2009/ Accepted 25 July 2009

Homotaurine (3-aminopropanesulfonate), a natural product and an analogue of GABA (4-aminobutyrate), was found to be a sole source of nitrogen for Cupriavidus necator (Ralstonia eutropha) H16, whose genome sequence is known. Homotaurine nitrogen was assimilated into cell material, and the quantitative fate of the organosulfonate was sulfopropanoate, which was recovered in the growth medium. The first scalar reaction was shown to be inducible homotaurine:2-oxoglutarate aminotransferase, which released 3-sulfopropanal from homotaurine. This aminotransferase was purified to homogeneity and characterized. Peptide mass fingerprinting yielded locus tag H16_B0981, which was annotated gabT, for GABA transaminase (EC 2.6.1.19). Inducible, NAD(P)+-coupled 3-sulfopropanal dehydrogenase, which yielded 3-sulfopropanoate from 3-sulfopropanal, was also purified and characterized. Peptide mass fingerprinting yielded locus tag H16_B0982, which was annotated gabD1, for succinate-semialdehyde dehydrogenase (EC 1.2.1.16). GabT and GabD1 were each induced during growth with GABA, and cotranscription of gabTD was observed. In other organisms, regulator GabC or GabR is encoded contiguous with gabTD: candidate GabR' was found in strain H16 and in many other organisms. An orthologue of the GABA permease (GabP), established in Escherichia coli, is present at H16_B1890, and it was transcribed constitutively. We presume that GabR'PTD are responsible for the inducible metabolism of homotaurine to intracellular 3-sulfopropanoate. The nature of the exporter of this highly charged compound was unclear until we realized from the sodium dodecyl sulfate-polyacrylamide gel electrophoresis data that sulfoacetaldehyde acetyltransferase (EC 2.3.3.15; H16_B1872) was strongly induced during growth with homotaurine and inferred that the sulfite exporter encoded at the end of the gene cluster (H16_B1874) has a broad substrate range that includes 3-sulfopropanoate.

* Corresponding author. Mailing address: Department of Biology, The University, D-78457 Konstanz, Germany. Phone: 49 7531 88 4247. Fax: 49 7531 88 2966. E-mail: alasdair.cook{at}uni-konstanz.de

{triangledown} Published ahead of print on 31 July 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, October 2009, p. 6052-6058, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.00678-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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