Autotransporters with GDSL passenger domains: molecular physiology and biotechnological applications.

Autotransporters are large proteins produced and secreted by Gram-negative bacteria. They consist of an N-terminal passenger domain, which typically harbours enzymatic activity and exerts a virulence function, and a C-terminal membrane anchor domain. Somehow, the membrane domain facilitates the transport of the passenger domain into the extracellular space. Several autotransporters possess hydrolase passenger domains that belong to the GDSL family of lipolytic enzymes. GDSL autotransporters represent a functionally distinct family and are characterized by several features of their passenger domains; these include 1) the absence of a conserved right-handed parallel β-helix, 2) lipolytic activity, and thus the capability to hydrolyse membranes, and 3) covalent attachment to the respective C-terminal β-domain, with the hydrolase domain exposed to the exterior. The esterase EstA of Pseudomonas aeruginosa is a typical enzyme of this type. Its physiological role was studied, its potential biotechnological application has been demonstrated, and its crystal structure was solved recently. Furthermore, it is capable of displaying different classes of enzymes in a range of Gram-negative bacteria including Escherichia coli, and FACS-based high-throughput screening for enantioselective esterases could be achieved using EstA.