Sweet Talk: Protein Glycosylation in Bacterial Interaction With the Host  Qiuhe Lu, Shan Li, Feng Shao  Trends in Microbiology  Volume 23, Issue 10, Pages 630-641 (October 2015) DOI: 10.1016/j.tim.2015.07.003 Copyright © 2015 Elsevier Ltd Terms and Conditions

Figure 1 Key Figure: Two Distinct Glycosylation Modifications Are Required for Citrobacter rodentium Colonization in Mice Citrobacter rodentium is a mouse model of human attaching–effacing enteropathogens, including enteropathogenic Escherichia coli (EPEC). The initial step in C. rodentium infection is adherence to intestinal epithelial cells, mediated by an autotransporter (named CARC) on the bacterial surface. The autotransporter, prior to crossing the bacterial inner membrane, is heptosylated by a BAHT (bacterial autotransporter heptosyltransferase)-family member on numerous serine residues in the passenger domain, and the modification is required for the adhesion. C. rodentium also harbors a type III secretion system (T3SS) effector NleB that monoglycosylates the death domain (DD) of TNFR1-associated death domain protein (TRADD), FAS-associated death domain protein (FADD), and receptor-interacting protein kinase 1 (RIPK1) downstream of tumor necrosis factor receptor 1 (TNFR1) or other death receptors. NleB is a unique GlcNAc transferase that modifies a conserved arginine in the DDs (inset). GlcNAcylated DDs are deficient in homotypic/heterotypic oligomerization, thereby blocking the assembly of signaling complexes downstream of the death receptor. As a result, NleB disrupts multiple tumor necrosis factor-α (TNFα)-activated signaling events, including activation of nuclear factor κB (NF-κB), apoptosis and necroptosis to counteract host immunity. The two glycosylation modifications mediated by the BAHT and NleB are both critically required for C. rodentium colonization of the gastrointestinal tract in infected mice. Trends in Microbiology 2015 23, 630-641DOI: (10.1016/j.tim.2015.07.003) Copyright © 2015 Elsevier Ltd Terms and Conditions

Figure 2 Glucosylation of Rho GTPases by Clostridium difficile Toxin A/B and Its Detection by the Pyrin Inflammasome. Toxin A/B (TcdA/B), the major virulence factors of C. difficile, enters into host cells through the endocytic route. TcdA/B features a glucosyltransferase domain that monoglucosylates Rho GTPases on a threonine residue (Thr-37 in RhoA). The modification inhibits the interaction of Rho GTPases with the guanine nucleotide dissociation inhibitor (GDI) as well as their nucleotide cycling catalysed by the GTPase-activating protein (GAP) and the guanine nucleotide exchange factors (GEFs). Glucosylated Rho GTPases are also impaired in activating their downstream effectors and are therefore functionally deficient in regulating actin cytoskeleton dynamics and other cellular processes. TcdA/B-mediated glucosylation and inactivation of Rho GTPases are detected by a cytosolic immune sensor, pyrin. Pyrin forms an inflammasome complex with the ASC (Apoptosis-associated Speck-like Protein Containing a Caspase Recruitment Domain) adaptor to activate caspase-1, an inflammatory caspase. Activated capase-1 processes pro-IL-1β/18 for maturation and triggers macrophage inflammatory death (pyroptosis), mounting antibacterial immune responses. Trends in Microbiology 2015 23, 630-641DOI: (10.1016/j.tim.2015.07.003) Copyright © 2015 Elsevier Ltd Terms and Conditions