Ability of MBP or RBP signal peptides to influence folding and in vitro translocation of wild-type and hybrid precursors.

Maltose-binding protein (MBP), whose export in E. coli is dependent upon the chaperone SecB, and ribose-binding protein (RBP), whose export is SecB-independent, have been used to generate hybrid secretory proteins. Here, in vitro techniques were used to analyze MBP, RBP, RBP-MBP (RBP signal and MBP mature), and MBP-RBP (MBP signal and RBP mature). In protease-protection experiments, RBP folded considerably faster than MBP, RBP-MBP, or MBP-RBP. Only the folding properties of proteins containing the MBP mature moiety were influenced by SecB. In post-translational translocation assays, MBP exhibited the highest translocation efficiency. The hybrids RBP-MBP and MBP-RBP showed intermediate levels, and RBP translocation was not detected in these assays. These experiments demonstrate the influence of the signal peptide in determining folding properties and translocation efficiency of precursor secretory proteins.