Folding in vitro and transport in vivo of pre-β-lactamase are SecB independent

The rate of folding of the precursor of beta-lactamase is not influenced by the presence of SecB under conditions in which GroEL/ES retards the folding. Wild-type beta-lactamase and several mutants in the signal or the mature protein, affecting either transport or enzyme kinetics and probably folding, were examined for total expression, total enzymatic activity, and transported beta-lactamase (in vivo resistance) in secB- and secB+ strains. We conclude that there is no indication of any relevant interaction between SecB and pre-beta-lactamase in vitro, nor did the secB- mutation affect the transport of wild-type beta-lactamase or any of the mutant in vivo. Thus, putative Escherichia coli "folding modulators' must be of limited specificity.