FIG 5.

Disassembly of VacA oligomers detected by negative-stain EM. WT VacA and the indicated mutants with paired cysteine substitutions were exposed to the indicated conditions (neutral pH with or without 100 mM DTT; acidic pH with or without 100 mM DTT) and then analyzed by negative-stain EM. WT VacA disassembled into monomers at pH 3 in the absence of DTT, whereas the mutant proteins retained an oligomeric structure under these conditions. Both low pH and the reducing agent were required for disassembly of the mutant proteins. Scale bars, 200 Å.