TRANSCRIPTIONAL REGULATION OF CYCLIC b-1,2-GLUCAN BIOSYNTHESIS IN BRUCELLA ABORTUS

ROSET MS, CIOCCHINI AE, UGALDE RA, IÑON DE IANNINO N.

Iguazu;, Misiones, Argentina.

Congreso; XL Reunion Anual de la Sociedad Argentina de Investigaciones en Bioquimica y Biologia Molecular (SAIB 2004); 2004

Sociedad Argentina de Investigaciones en Bioquimica y Biologia Molecular (SAIB)

Cyclic b-1,2-glucans are important components of gram negative bacterial envelope. In Brucella spp. the biosynthesis of cyclic b-1,2-glucan proceeds through a membrane-bound cyclic glucan synthase (Cgs) and secretion into the perisplasmic space through a membrane-bound cyclic glucan transporter (Cgt). It was observed that cgt mutant accumulates in the membrane higher amounts of Cgs protein than in the wild type. Accordingly, cgt mutant incorporates in vitro significant higher amount of [14C]-glucose into cyclic b-1,2-glucan and TCA insoluble glucoprotein. A cgs::lacZ transcriptional fusion was constructed and analyzed in three different backgrounds, wild type 2308, cgs and cgt mutants. Compare to wild type significant increment of â-galactosidase activity was observed in the cgt and cgs mutant backgrounds, thus suggesting that cyclic b-1,2-glucan is involved in the transcriptional regulation of cgs. Moreover complementation of cgs and cgt mutants with plasmids containing cgs or cgt inactive genes obtained by site-directed mutagenesis in the active site and the ATP binding site respectively, did not abolished this effect. These results strongly suggest that the absence of cyclic glucan in the periplasm and not the absence of proteins Cgt or Cgs in the membrane may be the signal that regulates transcription of cgs gene.