The arms race among microbes is a key driver in the evolution of not only the weapons but also defence mechanisms. Many gram-negative bacteria use the type six secretion system (T6SS) to deliver toxic effectors directly into neighbouring cells. Defence against effectors requires cognate immunity proteins. However, here we show immunity-independent protection mediated by envelope stress responses in Escherichia coli and Vibrio cholerae against a V. cholerae T6SS effector, TseH. We demonstrate that TseH is a PAAR-dependent species-specific effector highly potent against Aeromonas species but not against its V. cholerae immunity mutant or E. coli . Structural analysis reveals TseH is likely a NlpC/P60 family cysteine endopeptidase. We determine that two envelope stress response pathways, Rcs and BaeSR, protect E. coli from TseH toxicity by mechanisms including capsule synthesis. The two-component system WigKR (VxrAB) is critical for protecting V. cholerae from its own T6SS despite expressing immunity genes. WigR also regulates T6SS expression, suggesting a dual role in attack and defence. This deepens our understanding of how bacteria survive T6SS attacks and suggests that defending against the T6SS represents a major selective pressure driving the evolution of species-specific effectors and protective mechanisms mediated by envelope stress responses and capsule synthesis.

Many Gram-negative bacteria, including causative agents of dysentery, plague, and typhoid fever, rely on a type III secretion system – a multi-membrane spanning syringe-like apparatus – for their pathogenicity. The cytosolic ATPase complex of this injectisome is proposed to play an important role in energizing secretion events and substrate recognition. We present the 3.3 Å resolution cryo-EM structure of the enteropathogenic Escherichia coli ATPase EscN in complex with its central stalk EscO. The structure shows an asymmetric pore with different functional states captured in its six catalytic sites, details directly supporting a rotary catalytic mechanism analogous to that of the heterohexameric F1/V1-ATPases despite its homohexameric nature. Situated at the C-terminal opening of the EscN pore is one molecule of EscO, with primary interaction mediated through an electrostatic interface. The EscN-EscO structure provides significant atomic insights into how the ATPase contributes to type III secretion, including torque generation and binding of chaperone/substrate complexes.

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Background:The mycosin-1 protease (MycP1) is essential for export and cleavage of the type VII-secreted virulenceassociated proteins involved in pathogenesis of Mycobacterium tuberculosis and related species. Results: The x-ray structure of MycP1, with its proposed propeptide, is described. Conclusion:The proposed propeptide wraps around the perimeter of a subtilisin-like fold, leaving the catalytic center unobstructed. Significance: MycP1 may operate through a novel mode of regulation.

Considerable attention has been focused on the synthesis and chemical behavior of silylene-transition metal complexes. 1,2 Silyl(silylene) complexes L n M(dSiR 2 )-SiR 3 are one of the attractive synthetic targets since such complexes have been assumed to be key intermediates in many transition metal-catalyzed scrambling of substituents and skeletal redistribution of organosilicon and organosilicon-transition metal compounds. 2,3 Silyl-(silylene) complexes have been isolated as internal or external donor-stabilized complexes in which the electrondeficient silylene ligands are stabilized by coordination of two-electron donors. 4-7 Lappert et al. very recently reported the synthesis of the first donor-free silyl-(silylene) complex by the reaction of an isolable silylene and a platinum complex. 8 The silylene ligand in this complex is stabilized electronically by delocalization of lone pair electrons of two amino substituents attached to the silicon atom. There has been no base-free silyl-(silylene) complexes with only alkyl or aryl groups on the silicon atoms.In our previous work on donor-stabilized silyl(silylene) 6,7 and donor-free germyl(germylene)tungsten complexes, 9 we found that the tungsten fragment Cp′W(CO) 2 (Cp′ ) η-C 5 Me 5 , η-C 5 H 5 ) stabilizes the R 3 E-MdER 2 framework efficiently (E ) Si, Ge; M ) metal fragment). This prompted us to synthesize basefree silyl(silylene)tungsten complexes. Here we report the photolysis of a methyltungsten complex in the presence of hydrodisilanes. This reaction afforded either a monomeric base-free silyl(silylene)tungsten complex or a self-stabilized dimer of a silyl(silylene)tungsten complex depending on the sustituents on the silicon atoms.Photolysis of Cp′W(CO) 3 Me (1a, Cp′ ) Cp*, Cp* ) η-C 5 Me 5 ; 1b, Cp′ ) η-C 5 Me 4 Et) in the presence of excess HSiMe 2 SiMe 3 in hexane afforded yellow crystals of a self-stabilized silyl(silylene)tungsten complex with a dimeric structure, [Cp′W(CO) 2 (dSiMe 2 )(SiMe 3 )] 2 (2a, Cp′ ) Cp*; 2b, Cp′ ) η-C 5 Me 4 Et) in 87 and 54% yield, respectively (eq 1). Crystal structure analysis confirmed that complex 2b is the first silylene complex stabilized by coordination of an isocarbonyl ligand, which is coordinated to a tungsten fragment and a silylene ligand via its carbon and oxygen atom, respectively (Figure 1). The tungsten-silylene bond (W-Si(2) 2.489(2) Å) is significantly shorter than the tungsten-silyl bond (WSi(1) 2.609(2) Å), indicating partial double bond character for the W-Si (2) bonding. The silylene ligand is † Present address: Tobita, H.; Shimoi, M.; Ogino, H. J. Am. Chem. Soc. 1988, 110, 4092. (b) Tobita, H.; Ueno, K.; Shimoi, M.; Ogino, H.