Fig. 7.

ExbD D25 is important for ExbD-TonB disulfide-linked heterodimer formation. TCA-precipitated samples of strains expressing chromosomally encoded wild-type ExbD and TonB (W3110) or a ΔexbD ΔtolQR ΔtonB strain (KP1509) coexpressing plasmid-encoded TonB(C18G, A150C) and ExbD Cys substitutions without (−) or with (+) a D25N TMD substitution near native levels were resolved on nonreducing or reducing 13% and 11% SDS-polyacrylamide gels and immunoblotted with ExbD-specific polyclonal antibodies or TonB-specific monoclonal antibodies. Reduced and nonreduced samples came from the same culture. The positions of the monomeric proteins or disulfide-cross-linked complexes are indicated on the left. The positions of nonreducing molecular mass standards are indicated between the immunoblots. The strain designations across the top apply to both immunoblots below. All samples were processed on the same day.