Involvement of tryptophan in sodium dodecyl sulfate-induced conformation of K99 pilin

K99 pili from bovine strain B44 of Escherichia coli were incubated in a solution containing 1% sodium dodecyl sulfate (SDS), 4 M urea, 1% 2-mercaptoethanol (2-ME), and 10% glycerol at room temperature. After 2 weeks, there was a partial conversion of the pilin from its apparent molecular weight of 17,000 to 21,000 due to change in conformation as studied by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). After 10-12 weeks, this change in conformation was complete. The presence of 2-ME in the incubation mixture was essential for this change; this suggested the involvement of a disulfide bond. It was concluded that the disulfide bond and tryptophan residues of the pilin are essential for the change in conformation in SDS.