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Abstract Alphaviruses, such as chikungunya virus (CHIKV), are mosquito-borne viruses that represent a significant threat to human health due to the current context of global warming. Efficient alphavirus infection relies on the activity of the non-structural protein 3 (nsP3), a puzzling multifunctional molecule whose role in infection remains largely unknown. NsP3 is a component of the plasma membrane-bound viral RNA replication complex (vRC) essential for RNA amplification and is also found in large cytoplasmic aggregates of unknown function. Here, we report the cryo-electron microscopy (cryo-EM) structure of the CHIKV nsP3 at 2.35 Å resolution. We show that nsP3 assembles into tubular structures made by a helical arrangement of its alphavirus unique domain (AUD). The nsP3 helical scaffolds are consistent with crown structures found on tomographic reconstructions of the mature viral RCs. In addition, nsP3 helices assemble into cytoplasmic granules organized in a network of tubular structures that contain viral genomic RNA and capsid as well as host factors required for productive infection. Structure-guided mutagenesis identified residues that prevent or disturb nsP3 assemblies, resulting in impaired viral replication or transcription. Altogether, our results reveal an unexpected nsP3-dependent molecular organization essential for different phases of alphavirus infection.

Abstract The Mitochondrial Complex I Assembly (MCIA) complex is essential for the biogenesis of respiratory Complex I (CI), the first enzyme in the respiratory chain, which has been linked to Alzheimer’s disease (AD) pathogenesis. However, how MCIA facilitates CI assembly, and how it is linked with AD pathogenesis, is poorly understood. Here we report the structural basis of the complex formation between the MCIA subunits ECSIT and ACAD9. ECSIT binding induces a major conformational change in the FAD-binding loop of ACAD9, releasing the FAD cofactor and converting ACAD9 from a fatty acid β-oxidation (FAO) enzyme to a CI assembly factor. We provide evidence that ECSIT phosphorylation downregulates its association with ACAD9 and is reduced in neuronal cells upon exposure to amyloid-β (Aβ) oligomers. These findings advance our understanding of the MCIA complex assembly and suggest a possible role for ECSIT in the reprogramming of bioenergetic pathways linked to Aβ toxicity, a hallmark of AD.

Abstract Human Respiratory Syncytial Virus (HRSV) is a prevalent cause of severe respiratory infections in children and the elderly. The helical HRSV nucleocapsid is a template for the viral RNA synthesis and a scaffold for the virion assembly. This cryo-electron microscopy analysis reveals the non-canonical arrangement of the HRSV nucleocapsid helix, composed of 16 nucleoproteins per asymmetric unit, and the resulting systematic variations in the RNA accessibility. We demonstrate that this unique helical symmetry originates from longitudinal interactions by the C-terminal arm of the HRSV nucleoprotein. We explore the polymorphism of the nucleocapsid-like assemblies, report five structures of the full-length particles and two alternative arrangements formed by a C-terminally truncated nucleoprotein mutant, and demonstrate the functional importance of the identified longitudinal interfaces. We put all these findings in the context of the HRSV RNA synthesis machinery and delineate the structural basis for its further investigation.

The functional and biological significance of selected CASP13 targets are described by the authors of the structures. The structural biologists discuss the most interesting structural features of the target proteins and assess whether these features were correctly reproduced in the predictions submitted to the CASP13 experiment.

Jessop et. al. investigate the expression, activity, structure and supramolecular assembly of the arginine decarboxylase from Providencia stuartii, compare its polymers with those formed by the Escherichia coli lysine decarboxylase, and analyse the evolutionary conservation of the structural determinants of the polymerisation of these enzymes in enterobacteria.

This study examined the impact of a commonly adopted elementary universal social-emotional learning program, Second Step, on student social-emotional and academic outcomes following 2 years of implementation. The cluster-randomized wait-list control trial included 61 schools, 321 teachers, and 8,941 early elementary students across 2 states, with assessments collected in the fall and spring across 2 years. We developed 8 theoretically derived growth patterns that potentially described the intervention and counterfactual conditions, and then selected the model with the greatest support from the data for each outcome with an information-theoretic approach. Differences between intervention and control groups were tested within the best-fitting model in order to reduce misspecification and maximize generalizability. Most measures fit a pattern in which students improved only during instructional time in school and not during the summer; the data rarely fit the commonly assumed linear growth model. Improvements related to Second Step were observed for emotional symptoms, hyperactivity, skills for learning, and emotion management, but these were modified by either pretest levels or student sex. Condition effects for peer problems were larger for students with initially low ratings and for boys. Boys also showed improvements in conduct problems. Study impacts generally did not depend upon student grade level. The results confirmed the importance of identifying developmentally sensitive trajectories and suggested important implications for Second Step implementation in early elementary grades.

Motile bacteria sense chemical gradients with transmembrane receptors organised in supramolecular signalling arrays. Here authors introduce an E. coli strain that forms small minicells possessing extended and highly ordered chemosensory arrays that are visualized by cryo-electron tomography.

Binding of bacterial peptidoglycan muramyl dipeptides induces NOD2 activation and signalling via the downstream adaptor kinase RIP2. Here the authors show that RIP2 forms filaments via its CARD domain, analyse the structure of the CARD filaments and demonstrate the requirement of RIP2 polymerisation for the activation of NF-κB by NOD2.

The BCL10-MALT1 complex is a central signaling hub in lymphocytes and linked to various human immune pathologies. Here the authors present the cryo-EM structure of the BCL10-MALT1 filament core and verify the identified BCL10/MALT1 interface with mutagenesis studies.

Abstract During a proteolytically-driven maturation process, the orthoretroviral capsid protein (CA) assembles to form the convex shell that surrounds the viral genome. In some orthoretroviruses, including Rous Sarcoma Virus (RSV), CA carries a short and hydrophobic spacer peptide (SP) at its C-terminus early in the maturation process, which is progressively removed as maturation proceeds. In this work, we show that RSV CA assembles in vitro at near-physiological temperatures, forming hexamer tubes that effectively model the mature capsid surface. Tube assembly is strongly influenced by electrostatic effects, and is a nucleated process that remains thermodynamically favored at lower temperatures, but is effectively arrested by the large Gibbs energy barrier associated with nucleation. RSV CA tubes are multi-layered, being formed by nested and concentric tubes of capsid hexamers. However the spacer peptide acts as a layering determinant during tube assembly. If only a minor fraction of CA-SP is present, multi-layered tube formation is blocked, and single-layered tubes predominate. This likely prevents formation of biologically aberrant multi-layered capsids in the virion. The generation of single-layered hexamer tubes facilitated 3D helical image reconstruction from cryo-electron microscopy data, revealing the basic tube architecture.

Abstract Ancient dental pulps are highly precious samples because they conserve DNA from humans and blood-borne pathogens for ages. However, little is known about the microbial communities present in dental pulps. Here, we analyzed ancient and modern dental pulp samples from different time periods and geographic regions and found that they are colonized by distinct microbial communities, which can be differentiated from other oral cavity samples. We found that despite the presence of environmental bacteria, ancient dental pulps conserve a clear and well-conserved record of oral microbes. We were able to detect several different oral pathogens in ancient and modern dental pulps, which are commonly associated with periodontal diseases. We thus showed that ancient dental pulps are not only valuable sources of DNA from humans and systemic infections, but also an open window for the study of ancient oral microbiomes.

With the rapid improvement of cryo-electron microscopy (cryo-EM) resolution, new computational tools are needed to assist and improve upon atomic model building and refinement options. This communication demonstrates that microscopists can now collaborate with the players of the computer game Foldit to generate high-quality de novo structural models. This development could greatly speed the generation of excellent cryo-EM structures when used in addition to current methods.

Negative-strand RNA viruses condense their genome into helical nucleocapsids that constitute essential templates for viral replication and transcription. The intrinsic flexibility of nucleocapsids usually prevents their full-length structural characterisation at high resolution. Here, we describe purification of full-length recombinant metastable helical nucleocapsid of Hantaan virus (Hantaviridae family, Bunyavirales order) and determine its structure at 3.3 Å resolution by cryo-electron microscopy. The structure reveals the mechanisms of helical multimerisation via sub-domain exchanges between protomers and highlights nucleotide positions in a continuous positively charged groove compatible with viral genome binding. It uncovers key sites for future structure-based design of antivirals that are currently lacking to counteract life-threatening hantavirus infections. The structure also suggests a model of nucleoprotein-polymerase interaction that would enable replication and transcription solely upon local disruption of the nucleocapsid.

Dexamphetamine (AMPH) is a psychostimulant drug that is used both recreationally and as medication for attention deficit hyperactivity disorder. Preclinical studies have demonstrated that repeated exposure to AMPH can induce damage to nerve terminals of dopamine (DA) neurons. We here assessed the underlying neurobiological changes in the DA system following repeated AMPH exposure and pre-treated rats with AMPH or saline (4 times 5 mg/kg s.c., 2 hours apart), followed by a 1-week washout period. We then used pharmacological MRI (phMRI) with a methylphenidate (MPH) challenge, as a sensitive and non-invasive in-vivo measure of DAergic function. We subsequently validated the DA-ergic changes post-mortem, using a.o. high-performance liquid chromatography (HPLC) and autoradiography. In the AMPH pre-treated group, we observed a significantly larger BOLD response to the MPH challenge, particularly in DA-ergic brain areas and their downstream projections. Subsequent autoradiography studies showed that AMPH pre-treatment significantly reduced DA transporter (DAT) density in the caudate-putamen (CPu) and nucleus accumbens, whereas HPLC analysis revealed increases in the DA metabolite homovanillic acid in the CPu. Our results suggest that AMPH pre-treatment alters DAergic responsivity, a change that can be detected with phMRI in rats. These phMRI changes likely reflect increased DA release together with reduced DAT binding. The ability to assess subtle synaptic changes using phMRI is promising for both preclinical studies of drug discovery, and for clinical studies where phMRI can be a useful tool to non-invasively investigate DA abnormalities, e.g. in neuropsychiatric disorders.