Cadaverine induces closing of E. coli porins.

Abstract

We have used the electrophysiological technique of patch‐clamp to study the modulation of Escherichia coli porins by cadaverine. Porin channels typically have a very high probability to be open, and were not known to be inhibited by specific compounds until the present study. Experiments performed on patches of outer membrane reconstituted in liposomes reveal that cadaverine applied to the periplasmic side increases the frequency of channel closures in a concentration‐dependent fashion, and thereby decreases the total amount of ion flux through a porin‐containing membrane. The positive charge on cadaverine is important for inhibition, because the effect is relieved at higher pH where fewer polyamine molecules are charged. Modulation is observed only at negative pipet voltages, and therefore confers voltage dependence to porin activity. Cadaverine increases the number and duration of cooperative closures of more than one channel, suggesting that it does not merely block the pore but exerts its kinetic effect allosterically. As a biological assay of porin inhibition, E. coli behavior in chemotaxis swarm plates was tested and found to be impaired in the presence of cadaverine. Polyamines are naturally found associated with the outer membrane of E.coli, but are lost upon fractionation. We postulate that cadaverine might be a natural regulator of porin activity.

Polyamines Improve K+/Na+ Homeostasis in Barley Seedlings by Regulating Root Ion Channel Activities

“…These results suggested that polyamines may modulate ion channel activities through direct binding to the channel proteins. This view is consistent with previous findings carried out in both animal and bacterial cells (Delavega and Delcour, 1995;Johnson, 1996). It has been reported that several specific polyamine-binding proteins in plasma membranes from plant cells were well characterized (Tassoni et al, 1998(Tassoni et al, , 2002.…”

Complex Inhibition of OmpF and OmpC Bacterial Porins by Polyamines

“…However, the regulation of porin function by potentially physiologically relevant factors is still poorly understood. We showed recently that polyamines inhibit chemotaxis and flux of ␤-lactam antibiotics through porins and thus decrease the permeability of the outer membrane (17). In electrophysiological experiments, we also demonstrated that cadaverine induces closures of porins (18).…”

pH-induced Collapse of the Extracellular Loops ClosesEscherichia coli Maltoporin and Allows the Study of Asymmetric Sugar Binding

“…In particular, low pH leads to channel closure in the case of OmpF, OmpC, and PhoE (14 -17) and in a shift of the voltage dependence (18). Low pH may also be involved in cadaverine-mediated channel block (19). Atomic force microscopy of OmpF at low pH suggests that a conformation change of the loops exposed to the external surface is the reason for channel closure at low pH (20).…”