Structural insights into host GTPase isoform selection by a family of bacterial GEF mimics

Abstract

The Escherichia coli type III effector Map belongs to a large family of bacterial virulence factors that activate host Rho GTPase signaling pathways through an unknown molecular mechanism. Here we report direct evidence that Map functions as a potent and selective guanine-nucleotide exchange factor (GEF) for Cdc42. The 2.3-Å structure of the Map–Cdc42 complex revealed that Map mimics the GEF strategy of the mammalian Dbl family but has a three-dimensional architecture that is nearly identical to the bacterial GEF Salmonella spp. SopE. A comparative analysis between human and bacterial GEFs revealed a previously uncharacterized pairing mechanism between Map and the variable β2–3 interswitch region of Cdc42. We propose a GTPase selection model that is experimentally validated by the preferential activation Rac1 and RhoA by the Shigella spp. effectors IpgB1 and IpgB2, respectively. These results significantly expand the repertoire of bacterial GEF mimics and unify a GEF selection mechanism for host GTPase substrates.

Infection strategies of enteric pathogenic Escherichia coli

“…152 Map and SopE have been shown to have similar crystal structures when resolved in complex with Cdc42. 147 Despite the lack of sequence or structural similarity bacterial WxxxE effectors and eukaryotic GEFs appear to form the same conformational complex with Cdc42. The T3SS effector EspH was shown to subvert actin dynamics affecting filopodia and pedestal formation.…”

“…145 The Rho family small G proteins are crucial in the regulation of key cellular functions and the best characterized are Cdc42, Rac1 and RhoA, which trigger filopodia, lamellipodia/ruffles and stress fibers respectively. 146 T3SS effectors have been shown to regulate Rho GTPases by functioning as guanine exchange factors (GEFs), which control the switch from GDP-bound (inactive) to the GTP-bound (active) state, 147 or GTPase-activating proteins (GAPs), which increase the hydrolysis of GTP leading to the inactive state of the Rho GTPases. 148 Alto et al grouped 24 bacterial effector proteins in the WxxxE family based on a conserved motif of two invariant amino acids, Trp and Glu separated by three variable amino acids.…”

Perturbation of Maize Phenylpropanoid Metabolism by an AvrE Family Type III Effector fromPantoea stewartii

“…However, given that many T3Es have multiple targets, and given the large size of AvrE/HopR T3Es, it seems likely that WtsE might have multiple functions and targets within plant cells. The WxxxE motifs of AvrE family members are hypothesized to form part of the fold that mimics the active site of a guanine-exchange factor (GEF) protein and thus to modulate the activity of host GTPase proteins, as has been demonstrated for Map/IpgB/Sif family members from bacterial pathogens of animals (Huang et al, 2009). Confirmation of this biochemical prediction, along with localization in plant cells, have proven difficult due to the cell toxicity of the AvrE family T3Es (Ham et al, 2006).…”

Modern Aspects on <i>Shigella</i> Pathogenecity and Vaccine Development - A Review

“…Several type 3 secreted effectors including IpgB1 are involved in this process. IpgB1 is GEF (GTP exchange factor) (Huang et al, 2009) that localizes to host cell membranes at bacterial entry sites where it activates the small GTPase Rac and Cdc42 to induce membrane ruffling which promote the uptake of Shigella into host cells (Hachani et The most frequently linked with endemic outbreaks of shigellosis are caused by S. flexneri strains. They invade the colonic and rectal epithelium of their host and cause severe tissue damage.…”