Dissimilation of cysteate via 3-sulfolactate sulfo-lyase and a sulfate exporter in Paracoccus pantotrophus NKNCYSA

Abstract

Paracoccus pantotrophus NKNCYSA utilizes (R)-cysteate (2-amino-3-sulfopropionate) as a sole source of carbon and energy for growth, with either nitrate or molecular oxygen as terminal electron acceptor, and the specific utilization rate of cysteate is about 2 mkat (kg protein) "1 .The initial degradative reaction is catalysed by an (R)-cysteate : 2-oxoglutarate aminotransferase, which yields 3-sulfopyruvate. The latter was reduced to 3-sulfolactate by an NAD-linked sulfolactate dehydrogenase [3?3 mkat (kg protein) "1 ]. The inducible desulfonation reaction was not detected initially in cell extracts. However, a strongly induced protein with subunits of 8 kDa (a) and 42 kDa (b) was found and purified. The corresponding genes had similarities to those encoding altronate dehydratases, which often require iron for activity. The purified enzyme could then be shown to convert 3-sulfolactate to sulfite and pyruvate and it was termed sulfolactate sulfo-lyase (Suy). A high level of sulfite dehydrogenase was also induced during growth with cysteate, and the organism excreted sulfate. A putative regulator, OrfR, was encoded upstream of suyAB on the reverse strand. Downstream of suyAB was suyZ, which was cotranscribed with suyB. The gene, an allele of tauZ, encoded a putative membrane protein with transmembrane helices (COG2855), and is a candidate to encode the sulfate exporter needed to maintain homeostasis during desulfonation. suyAB-like genes are widespread in sequenced genomes and environmental samples where, in contrast to the current annotation, several presumably encode the desulfonation of 3-sulfolactate, a component of bacterial spores.

The sulfonated osmolyte N-methyltaurine is dissimilated by Alcaligenes faecalis and by Paracoccus versutus with release of methylamine

“…This compound is oxidized to sulfate by the undefined sulfite dehydrogenase which is assayed with ferricyanide as the electron acceptor (Table 1), and the sulfate is excreted. The mechanism of excretion is unknown, but candidate gene products (TauZ in a-Proteobacteria and OrfX in b-Proteobacteria) are known in other systems (Rein et al, 2005). The mechanism of excretion of methylamine (Figs 1 and 2) is also unknown, but might be performed by the ammonium-methylamine transporter AmtB (Khademi et al, 2004;Booth et al, 2005).…”

“…The export of methylamine (III) and sulfate (VI) is deduced from earlier work (e.g. Brü ggemann et al, 2004;Rein et al, 2005).…”

“…In a range of a-Proteobacteria, e.g. Paracoccus pantotrophus NKNCYSA, a regulated eightgene cluster, tauABCXY-xsc-tauZ-pta, is believed to encode an ABC transporter for taurine (TauABC), taurine dehydrogenase (TauXY), Xsc, a putative sulfate exporter (TauZ) and phosphotransacetylase (Pta) (Brüggemann et al, 2004;Rein et al, 2005;J. Ruff & T. H. M. Smits, unpublished).…”

Genome-enabled analysis of the utilization of taurine as sole source of carbon or of nitrogen by Rhodobacter sphaeroides 2.4.1

“…Malyl-CoA lyase was assayed as described elsewhere (Meister et al, 2005). Anionexchange and hydrophobic interaction chromatography were done with soluble fractions free of nucleic acids as described elsewhere (Ruff et al, 2003;Rein et al, 2005).…”

“…The xsc gene of R. sphaeroides 2.4.1 has a high level (87 %) of identity to the orthologue encoding a purified Xsc in the phylogenetically related Paracoccus denitrificans NKNIS (Brüggemann et al, 2004). The tauZ gene is presumed to encode a sulfate exporter (Rein et al, 2005). The group of pta genes is well known, but the enzyme is seldom characterized (Lawrence et al, 2006).…”