Fluorescein analogues inhibit SecA ATPase: the first sub-micromolar inhibitor of bacterial protein translocation

SecA is a central component of the general secretion system that is essential for bacterial growth and thus an ideal target for antimicrobial agents. A series of fluorescein analogues were first screened against the ATPase activity using the truncated unregulated SecA catalytic domain. Rose bengal (RB) and erythrosin B (EB) were found to be potent inhibitors SecA with IC(50) values of 0.5 μM and 2 μM, respectively. RB and EB inhibit the catalytic SecA ATPase more effectively than the F(1) F(0) -proton ATPase. We used three assays to test the effect of these compounds on full-length SecA ATPase: in solution (intrinsic ATPase), in membrane preparation, and translocation ATPase. RB and EB show the following trend in terms of IC(50) values: translocation ATPase