Antigen 43-Mediated Autotransporter Display, a Versatile Bacterial Cell Surface Presentation System

Antigen 43 (Ag43), a self-recognizing outer membrane protein of Escherichia coli, has been converted into an efficient and versatile tool for surface display of foreign protein segments. Ag43 is an autotransporter protein characterized by the feature that all information required for transport to the outer membrane and secretion through the cell envelope is contained within the protein itself. Ag43 consists of two subunits (α and β), where the β-subunit forms an integral outer membrane translocator to which the α-subunit is noncovalently attached. The simplicity of the Ag43 system makes it ideally suited as a surface display scaffold. Here we demonstrate that the Ag43 α-module can accommodate and display correctly folded inserts and has the ability to display entire functional protein domains, exemplified by the FimH lectin domain. The presence of heterologous cysteine bridges does not interfere with surface display, and Ag43 chimeras are correctly processed into α- and β-modules, offering optional and easy release of the chimeric α-subunits. Furthermore, Ag43 can be displayed in many gram-negative bacteria. This feature is exploited for display of our chimeras in an attenuated Salmonella strain.