A C-terminal amidated microcin J25 derivative has antimicrobial activity independent of RNA polymerase inhibition

BELLOMIO, AUGUSTO; VINCENT, PAULA A.; ARCURI, BEATRIZ FERNANDEZ DE; FARÍAS, RICARDO N.; SALOMÓN, RAUL A.; MORERO, ROBERTO D.

Iguazú, Misiones - Argentina

Congreso; Saib XL Annual Meeting; 2004

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

    Microcin J25 (MccJ25) is a 21-amino-acid antimicrobial peptide secreted by Escherichia coli. It has a dual mechanism of action: on the one hand, it inhibits transcription by binding within and obstructing the RNA polymerase (RNAP) secondary channel; on the other hand, it inhibits cell respiration with superoxide radical production. We synthesized a C-terminal amidated MccJ25 derivative (MccJ25*) which does not have any effect on RNAP in vivo or in vitro. The E. coli strain AB259, which shows turbid inhibition halos with MccJ25 in a spot-on-lawn test, was resistant to MccJ25* on M9 medium, while E. coli AB1133, a hypersusceptible strain, which gives clear spots with  MccJ250, was susceptible to MccJ25*. A RNAP mutation (rpoC T931I) in AB259 strain causes resistance to MccJ25. When this mutation was transduced to AB1133 the transductant strain PA232 showed a residual sensitivity to the antibiotic. Similar to MccJ25, MccJ25* inhibited the growth, oxygen consumption and respiratory enzyme activities on PA232 (pGC01) strain, which overexpresses FhuA, the outer membrane receptor  for MccJ25.     These results led us to conclude that the MccJ25 C-terminal region is very important for RNAP inhibition and that the MccJ25* residual antimicrobial activity on E. coli strain AB1133  could be explained by inhibition of cell respiration.