Peptides inhibiting the type three secretion system (TTSS) from enteropathogenic and enterohemorrhagic Escherichia coli

M. LARZÁBAL; D. VILTE; E. MERCADO; H. SALAZAR; F. NAVARRO GARCÍA; A.CATALDI

Buenos Aires

Simposio; 7th International Simposium on Shiga Toxin (Verocitotoxin)- producing Escherichia coli infections; 2009

  Introduction Enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC) are two categories of E. coli strains associated with human disease. A major virulence factor of both pathotypes is the expression of a type three secretion system (TTSS), responsible of their ability to adhere to gut mucosa with a characteristic attaching and effacing lesion (A/E). The TTSS translocates effector proteins that subvert mammalian cell biochemistry, directly into host cell. It is known that some proteins that have an important role in the formation of the TTSS structure interacts by coiled– coil regions. Aim Synthetic peptides , whose sequences were derived from coiled-coil regions of EspA and EscF proteins, we designed and analyzed to inhibit the TTSS. Discussion The peptides mimicking EspA  (CoilA and CoilB) were effective in inhibiting the TTSS dependent hemolysis of red blood cells by the EPEC E2348/69 strain. CoilA and CoilB peptides also reduced the formation of actin pedestals by the same strain in HEp-2 cells and impaired the TTSS-mediated protein translocation into the epithelial cell. Interestingly, CoilA and CoilB were able to block EspA assembly, destabilizing the TTSS and thereby Tir translocation. This blockage of EspA polymerization by CoilA or CoilB peptides, also inhibited the correct delivery of EspB and EspD as detected by immunoblotting. Interestingly, electron microscopy of bacteria incubated with the CoilA peptide showed a reduction of the length of EspA filaments. This suggests that coiled-coil peptides can prevent the assembly and thus the functionality of the TTSS apparatus. In summary, our results indicate that these peptides could provide an attractive tool to prevent EPEC and EHEC pathogenesis. The peptides mimicking EspA (CoilA and CoilB) reduced the secretion of EspD and EspD/EspB respectively thus avoiding the interaction between the proteins responsible for cell formation pore and EspA. This explains the inhibition in the Red Blood cell assay and inability to translocating TIR into the HEp-2 cells and consequently does not allow A/E (FAS assay).