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. 2016 Apr 22;291(26):13520–13528. doi: 10.1074/jbc.M116.729103

FIGURE 6.

FIGURE 6.

Sec signal peptides do not support folding of CueO. The signal peptide of CueO was substituted by the Sec signal peptides of DsbA (co-translational transport) and MalE (post-translational transport; some additional residues were included to ensure proper cleavage), and the solubility of the protein products was monitored by Western blotting using cell debris/inclusion body fractions (IB) and soluble fractions (S). The signal peptides of all constructs are shown at the left of the respective blots, with their h-regions underlined and the cleavage site indicated by an arrow. DnaK was detected in the soluble fraction as control. Note that the soluble wt-CueO is rendered insoluble when its authentic Tat signal peptide is exchanged by a Sec signal peptide. The lower blot compares the inclusion body signal of MalE(SP)-CueO and DsbA(SP)-CueO (IB) with a mixture of precursor and mature CueO. The processing of the two Sec signal peptides is suggestive for aggregation after transport.