“The Leucine Responsive Regulatory Protein (Lrp) is involved in MccJ25 resistence”

SOCÍAS, SERGIO B., VINCENT PAULA A., SALOMON, RAÚL A.

Misiones, Argentina

Congreso; Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular.; 2004

Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular (SAIB)

THE LEUCINE-RESPONSIVE REGULATORY PROTEIN (LRP) IS INVOLVED IN MccJ25 RESISTANCE Socías Benjamín, Vincent Paula A., Salomón Raúl A. Dep. de Bioquímica de la Nutrición. INSIBIO (UNT-CONICET. Inst. de Química Biológica. Fac. de Bioqca. Qca. y Fcia. UNT-4000. Tucumán E-mail: salomon@unt.edu.ar  We have observed an intrinsic resistance of several E coli strains to the peptide antibiotic MccJ25. We found that inactivation of one of the genes of leucine (Leu) biosynthesis increases sensitivity to MccJ25. In addition, there was a greater sensitivity to the antibiotic when the Leu concentration in the medium was increased. Intracellular amount of the global transcriptional regulator Lrp inversely depends on Leu concentration. E coli RO64, an lrp null mutant, did not show the Leu effect on MccJ25 sensitivity..Moreover, RO64was hypersusceptible to the antibiotic. A possible explanation of these results is that Lrp either negatively affects  the import or increases the export of MccJ25. We searched for a consensus sequence for Lrp binding (TTTATTCtNaAT) in the genes involved in MccJ25 import and export. We found two potential Lrp binding sites (one of these identical to the consensus) just upstream of yojI, a chromosomal gene which codes for a MccJ25 pump. To prove that Lrp is a positive regulator of yojI transcription, we transformed lrp+ and lrp- strains with a plasmid carrying yojI+.  Lrp+ transformants displayed complete resistance to MccJ25, while the sensitivity of Lrp- strain remained unchanged. We conclude that an increased Leu concentration reduces yojI transcription, and therefore MccJ25 export, through a decresed intracelelar level of Lrp.