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The assembly, architecture and role of the bacterial type VI secretion system (T6SS) membrane core complex is presented.

The basic features of dopamine release sites are still largely unknown. Here, the authors determine the ultrastructure of fluorescent dopaminergic and glutamatergic synaptosomes in mouse striatum using cryo-correlative light and electron microscopy.

The asymmetric distribution of lipopolysaccharide (LPS) on the surface of the bacterial outer membrane is essential and crucial for antibiotic resistance. Here, authors characterize the LPS translocon holo-complex, LptDEMY, uncovering conformational translocon state transitions that might explain how LPS is assembled at the outer membrane surface.

Type IV secretion systems (T4SSs) are found in both Gram-negative and Gram-positive bacteria and generally comprise 12 protein components that are organized into ATP-powered, double-membrane-spanning complexes. Here, Fronzes, Christie and Waksman review the structural data of many T4SS components and propose a model for the assembly of a functional type IV secretion apparatus.

Rearrangement hot spots (Rhs) proteins are bacterial polymorphic toxin systems. Here, the authors show that Rhs1 forms a complex with the Type VI secretion system (T6SS) spike protein VgrG and the EagR chaperone. They also present the cryo-EM structure of the Rhs1-EagR complex and propose a model for Rhs loading and delivery by the T6SS.

Here, Anger et al. report the structure of the type 4 pilus (T4P) from Streptococcus sanguinis. They show that the T4P architecture seen in diderm bacteria – where the N-terminal α-helices of pilin subunits are partially unfolded upon polymerisation – is conserved in distant monoderm species.

Type IV secretion systems span the two membranes of Gram-negative bacteria, with three proteins —— VirB7, VirB9 and VirB10 — assembled into a 1.05 megadalton core spanning the inner and outer membranes. Here, the crystal structure of an outer-membrane complex is presented. The structure is the largest determined for an outer-membrane channel and is unprecedented in being composed of three proteins.

Acetaldehyde–alcohol dehydrogenase (AdhE) converts acetyl-CoA to ethanol and is a key enzyme in bacterial alcoholic fermentation. AdhE forms spirosomes and, here, the authors present the cryoEM structures of compact and extended E.coli AdhE spirosomes and show that the extended conformation is the catalytically active form of the enzyme and discuss mechanistic implications.

The cryo-EM structure of the TssKFGE baseplate wedge complex of the type VI secretion system (T6SS) from enteroaggregative Escherichia coli helps to elucidate the molecular architecture of the whole T6SS baseplate, and its assembly and mode of action.

Bacterial homologous recombination involves the actions of RadA and RecA to promote single-stranded DNA integration. Here the authors report the structure of RadA fromStreptococcus pneumoniaeand demonstrate that it acts as a hexameric DnaB-type helicase.

Dynamic nuclear polarization–based solid-state nuclear magnetic resonance spectroscopyis applied to study the structure of a large bacterial membrane protein complex in its cellular environment.

Using biochemistry, cell biological, X-ray crystallography and cryo-EM methods, Maisonneuve et al. reveal how the scaffolding proteins CNK and HYP enhance the binding of KSR to MEK, which in turn allosterically controls RAF activation in Drosophila.

The three-dimensional structure of the type IV secretion system encoded by the Escherichia coli R388 conjugative plasmid.

CsgG and CgsE form an encaging translocon for selective, iterative diffusion of curli subunits across the non-energized bacterial outer membrane.

Many Gram-negative bacteria secrete exopolysaccharides via functionally homologous synthase-dependent systems. Here the authors use electron microscopy to reveal that biofilm-promoting cellulose in E. coli is secreted by a conserved multi-component secretion system with a megadalton-sized asymmetric architecture.

A combination of X-ray crystallography, electron microscopy, functional assays and time-lapse fluorescence microscopy shows that a protein of previously unknown function, TssA, forms a dodecameric complex that interacts with components of the tube and sheath of the type VI secretion system of bacteria, and that it primes and coordinates biogenesis of both the tail tube and the sheath.

Nanobody-aided X-ray crystallography and cryo-electron microscopy are used to describe the Ca²⁺-dependent polymerization dynamics of the S-layer of the Geobacillus stearothermophilus cell wall.