A C-terminal disulphide bond impairs the secretion of full-length OtpA.
A. The location of the cysteine residues in OtpAcys is shown.
B–C. HDB114 (B) or PC97 (C) transformed with pPC11 (PBAD-otpB) and pPC105 (Ptrc-otpAcys) were incubated with IPTG and arabinose and then subjected to pulse-chase labelling. Cultures were divided into cell (C) and secreted (S) fractions and half of the cells were treated with proteinase K (PK). OtpA was immunoprecipitated from all samples. The S samples were derived from twice as much culture volume as each C sample. m, molecular weight markers.