SPATEs

SPATEs, or serine protease autotransporters of Enterobacteriaceae, constitute a family of secreted virulence factors found in several members of the Enterobacteriaceae, including Escherichia coli and Shigella species. They are autotransporters secreted by the Type V secretion system and are characterized by a C-terminal beta-barrel translocator domain that inserts into the outer membrane and an N-terminal passenger domain that contains the serine protease activity.

The typical SPATE protein architecture consists of a signal peptide, a passenger domain with the catalytic serine protease motif, and a C-terminal beta-barrel translocator responsible for translocation to the cell surface and eventual release of the passenger domain. The passenger domain can be released from the cell surface or remain tethered, and the protease activity targets diverse host substrates. Substrates include mucins, immunoglobulins, and components of the cytoskeleton; some SPATEs also disrupt epithelial barrier function and modulate immune responses, contributing to diarrheal disease and other infections.

SPATEs are commonly divided into two broad classes. Class 1 SPATEs generally exhibit cytotoxic activities that damage host cells, often by targeting cytoskeletal or other structural proteins. Class 2 SPATEs are frequently associated with mucin degradation and colonization, aiding bacteria in establishing infection and traversing mucosal surfaces. Numerous SPATEs have been studied, including Pet, Sat, Pic, Vat, and SigA, each contributing in different ways to pathogenicity.

In research, SPATEs are examined for their roles in virulence, their mechanisms of substrate recognition, and their potential as targets for vaccines or therapeutics.