Crystal structure of a subtilisin-like autotransporter passenger domain reveals insights into its cytotoxic function

Autotransporters are bacterial proteins that possess multiple activities associated with pathogenesis. Here the authors present the structure of the autotransporter subtilase Ssp from Serratia marcescens and show that its distinctive structural features are required for its cytotoxic function. Autotransporters (ATs) are a large family of bacterial secreted and outer membrane proteins that encompass a wide range of enzymatic activities frequently associated with pathogenic phenotypes. We present the structural and functional characterisation of a subtilase autotransporter, Ssp, from the opportunistic pathogen Serratia marcescens. Although the structures of subtilases have been well documented, this subtilisin-like protein is associated with a 248 residue beta-helix and itself includes three finger-like protrusions around its active site involved in substrate interactions. We further reveal that the activity of the subtilase AT is required for entry into epithelial cells as well as causing cellular toxicity. The Ssp structure not only provides details about the subtilase ATs, but also reveals a common framework and function to more distantly related ATs. As such these findings also represent a significant step forward toward understanding the molecular mechanisms underlying the functional divergence in the large AT superfamily.

Automated summary

Researchers reveal the structural features of the bacterial protein autotransporter Ssp and its association with cytotoxic function.