Bacterial LPX motif-harboring virulence factors constitute a species-spanning family of cell-penetrating effectors
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Effector proteins are key virulence factors of pathogenic bacteria that target and subvert the functions of essential host defense mechanisms. Typically, these proteins are delivered into infected host cells via the type III secretion system (T3SS). Recently, however, several effector proteins have been found to enter host cells in a T3SS-independent manner thereby widening the potential range of these virulence factors. Prototypes of such bacteria-derived cell-penetrating effectors (CPEs) are the Yersinia enterocolitica-derived YopM as well as the Salmonella typhimurium effector SspH1. Here, we investigated specifically the group of bacterial LPX effector proteins comprising the Shigella IpaH proteins, which constitute a subtype of the leucine-rich repeat protein family and share significant homologies in sequence and structure. With particular emphasis on the Shigella-effector IpaH9.8, uptake into eukaryotic cell lines was shown. Recombinant IpaH9.8 (rIpaH9.8) is internalized via endocytic mechanisms and follows the endo-lysosomal pathway before escaping into the cytosol. The N-terminal alpha-helical domain of IpaH9.8 was identified as the protein transduction domain required for its CPE ability as well as for being able to deliver other proteinaceous cargo. rIpaH9.8 is functional as an ubiquitin E3 ligase and targets NEMO for poly-ubiquitination upon cell penetration. Strikingly, we could also detect other recombinant LPX effector proteins from Shigella and Salmonella intracellularly when applied to eukaryotic cells. In this study, we provide further evidence for the general concept of T3SS-independent translocation by identifying novel cell-penetrating features of these LPX effectors revealing an abundant species-spanning family of CPE.
KeywordsBacterial cell-penetrating effector proteins E3 ubiquitin ligase IpaH Endocytosis Endosomal escape LPX effector protein family
We like to thank our colleagues of the Institute of Infectiology for fruitful discussions and their valuable contributions.
This study was supported by Grants from the Deutsche Forschungsgemeinschaft (DFG, RU1884/2-1 to CR, SFB1009 TP B03 to CR and MAS), by the DFG Graduiertenkolleg GRK1409, the Cells-in-Motion Cluster of Excellence (EXC 1003-CiM), and by a Grant from the Interdisciplinary Centre for Clinical Research (IZKF, Rüt2/002/16 to CR) of the Medical Faculty of the University of Münster. The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
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