Fk. Bahrani et al., SECRETION OF IPA PROTEINS BY SHIGELLA-FLEXNERI - INDUCER MOLECULES AND KINETICS OF ACTIVATION, Infection and immunity, 65(10), 1997, pp. 4005-4010
The type III Mxi-Spa secretion machinery of Shigella flexneri is respo
nsible for secretion of Ipa proteins, which are involved in the entry
of bacteria into epithelial cells. Ipa proteins accumulate within bact
eria growing in laboratory media, and their secretion is activated upo
n contact of bacteria with eukaryotic cells. In this study, we have id
entified a group of chemical compounds, including Congo red, Evans blu
e, and direct orange, which are able to induce secretion of Ipa protei
ns by bacteria suspended in phosphate-buffered saline. Parameters of k
inetics of activation of Ipa secretion by Congo red were determined by
measuring by enzyme-linked immunosorbent assay the amount of IpaC sec
reted and by investigating the increase in susceptibility of Ipa prote
ins to proteinase K degradation. Ipa secretion occurred at 37 degrees
C, was obtained with 5 to 10 mu M Congo red, and was complete within 3
0 min, In addition, activation of Ipa secretion by Congo red was obser
ved with bacteria harvested throughout the exponential phase of growth
but not with bacteria in the stationary phase. The interactions of Co
ngo red and Congo red-related compounds with the Mxi-Spa secretion app
aratus might be specific hydrophobic interactions similar to those inv
olved in binding of Congo red to amyloid proteins.