Pet is one of the serine protease
autotransporters of the Enterobacteriaceae (SPATEs) that
releases passenger domain from the b-domain by nucleophilic
attack, without requiring exogenous protease. Using the system,
protein fusions were produced extracellularly up to
5.4 mg/l, representing as much as 5% of total cellular protein
in shaker flask cultivation. Interestingly, the authors in the
same study provided additional evidence that other SPATEs
could also be used to secrete proteins. One drawback of the
system is that only 50% of the protein produced was found in
culture medium and the rest on the surface, thus an
improvement evidently is needed. An interesting application
of autotransporter for consolidated bioprocessing was provided
by Wargacki et al