Fig. 1. Structural organization of the IgA protease and HEβ hybrid. (A) Schematic representation of the IgA protease precursor (∼170 kDa) from N.gonorroheae showing the position of the N-terminal signal sequence (ss), the secreted protease module (∼120 kDa) and the transporter C-domain (∼45 kDa; C-IgAP). The ∼30 kDa β-core region within C-IgAP is also labeled. (B) Organization of the relevant insert of plasmid pHEβ encoding the HEβ hybrid under the control of the IPTG-inducible lac promoter (plac). The heb gene chimera is an in-frame fusion of DNA segments encoding the pelB N-terminal signal sequence (ss), polyhistidine (6×his) and E-tag peptides, and the C-IgAP transporter domain. The site of cleavage of the signal peptidase (just before the His₆ peptide) is indicated by an arrowhead. (C) Representation of topology of HEβ in the OM showing the His₆ N-passenger domain exposed to the extracellular space (Out) and the C-terminus toward the periplasm. The putative β-barrel of HEβ is depicted as a cylinder embedded in the OM.