| Description |
Bacterial flagellar motors rotate, obtaining energy from a transmembrane proton gradient. The mechanism of torque generation is not known, but must involve communication between the stator protein MotA and the rotor protein FliG. Previous studies identified charged residues in both MotA and FliG that are essential for torque generation. They are Arg 90 and Glu 98 in MotA; and Arg 281, Asp 288, and Asp 289 in FliG. The essential charged residues in MotA interact electrostatically with those in FliG. In this thesis, I characterize motor function in several mutants with alterations in one or more of these charged residues. Motor performance in various mutants was measured in D20 and H20, and in media of varying ionic strength or viscosity. Performance was measured at high load by tethered cell assays and at low load by measurements of swimming speed. The results indicate that the charged residues function to make motor rotation rapid at low load, and not primarily to maximize torque production at high loads. These residues do not appear to participate directly in the proton conduction pathway. |
