Abstract
Antigen 43 (Ag43) is an autotransporter encoded by the metastable flu gene that mediates autoaggregation and flocculation in Escherichia coli. As a member of the type V secretion system, Ag43 is translocated to the outer membrane via the SecYEG translocon and the Bam complex. During this process, cleavage is expected to occur first between the signal peptide and passenger domain by SecYEG, followed by a second cleavage event between the passenger and autochaperon domains by an as-yet unidentified factor. These sequential processing events are predicted to produce three distinct protein fragments; In this study, we investigated Ag43 expression and time-dependent cleavage within E. coli BL21, DH5a and BW25113 strains, utilizing an arabinose inducible plasmid encoding Ag43. Within western blotting analysis, we show that the expected banding pattern for the current cleavage model was not observed, and propose revised models for Ag43 outer membrane translocation and processing in E. coli.