Fig. 6.

Competition for fluorescein maleimide labeling of Phe615Cys mutant AcrB Binding protomer by some substrates of the pump. (A Left) composition of each construct tested. (Right) The extent of labeling was tested with 40 μM fluorescein maleimide and without competitors on all protomer units of the covalently linked AcrB trimer, in which the first protomer was forced to take the Extrusion conformation by the introduction of Asp407Asn mutation. (B) Potential competitors were added at different concentrations, and the extent of fluorescein labeling of the mutant AcrB was assessed as described in the Experimental Procedures, by using 20 μM fluorescein-5-maleimide.