Rift Valley fever virus (RVFV), like many other Bunyaviridae family members, is an emerging human and animal pathogen. Bunyaviruses have an outer lipid envelope bearing two glycoproteins, G N and G C , required for cell entry. Bunyaviruses deliver their genome into the host-cell cytoplasm by fusing their envelope with an endosomal membrane. The molecular mechanism of this key entry step is unknown. The crystal structure of RVFV G C reveals a class II fusion protein architecture found previously in flaviviruses and alphaviruses. The structure identifies G C as the effector of membrane fusion and provides a direct view of the membrane anchor that initiates fusion. A structure of nonglycosylated G C reveals an extended conformation that may represent a fusion intermediate. Unanticipated similarities between G C and flavivirus envelope proteins reveal an evolutionary link between the two virus families and provide insights into the organization of G C in the outer shell of RVFV.

SARM1, an executor of axonal degeneration, displays NADase activity that depletes the key cellular metabolite, NAD+, in response to nerve injury. The basis of SARM1 inhibition and its activation under stress conditions are still unknown. Here, we present cryo-EM maps of SARM1 at 2.9 and 2.7 Å resolutions. These indicate that SARM1 homo-octamer avoids premature activation by assuming a packed conformation, with ordered inner and peripheral rings, that prevents dimerization and activation of the catalytic domains. This inactive conformation is stabilized by binding of SARM1’s own substrate NAD+ in an allosteric location, away from the catalytic sites. This model was validated by mutagenesis of the allosteric site, which led to constitutively active SARM1. We propose that the reduction of cellular NAD+ concentration contributes to the disassembly of SARM1's peripheral ring, which allows formation of active NADase domain dimers, thereby further depleting NAD+ to cause an energetic catastrophe and cell death.

BACKGROUND & AIM: Patients with inflammatory bowel diseases (IBD), specifically those treated with anti-tumor necrosis factor (TNF)a biologics, are at high risk for vaccine-preventable infections. Their ability to mount adequate vaccine responses is unclear. The aim of the study was to assess serologic responses to messenger RNA-Coronavirus Disease 2019 vaccine, and safety profile, in patients with IBD stratified according to therapy, compared with healthy controls (HCs). METHODS: Prospective, controlled, multicenter Israeli study. Subjects enrolled received 2 BNT162b2 (Pfizer/BioNTech) doses. Anti-Gastroenterology 2021;-:1-14 CLINICAL ATspike antibody levels and functional activity, anti-TNFa levels and adverse events (AEs) were detected longitudinally. RE-SULTS: Overall, 258 subjects: 185 IBD (67 treated with anti-TNFa, 118 non-anti-TNFa), and 73 HCs. After the first vaccine dose, all HCs were seropositive, whereas w7% of patients with IBD, regardless of treatment, remained seronegative. After the second dose, all subjects were seropositive, however anti-spike levels were significantly lower in anti-TNFa treated compared with non-anti-TNFa treated patients, and HCs (both P < .001). Neutralizing and inhibitory functions were both lower in anti-TNFa treated compared with non-anti-TNFa treated patients, and HCs (P < .03; P < .0001, respectively). Anti-TNFa drug levels and vaccine responses did not affect anti-spike levels. Infection rate (w2%) and AEs were comparable in all groups. IBD activity was unaffected by BNT162b2. CONCLUSIONS: In this prospective study in patients with IBD stratified according to treatment, all patients mounted serologic response to 2 doses of BNT162b2; however, its magnitude was significantly lower in patients treated with anti-TNFa, regardless of administration timing and drug levels. Vaccine was safe. As vaccine serologic response longevity in this group may be limited, vaccine booster dose should be considered.

Dengue virus relies on a conformational change in its envelope protein, E, to fuse the viral lipid membrane with the endosomal membrane and thereby deliver the viral genome into the cytosol. We have determined the crystal structure of a soluble fragment E (sE) of dengue virus type 1 (DEN-1). The protein is in the postfusion conformation even though it was not exposed to a lipid membrane or detergent. At the domain I-domain III interface, 4 polar residues form a tight cluster that is absent in other flaviviral postfusion structures. Two of these residues, His-282 and His-317, are conserved in flaviviruses and are part of the "pH sensor" that triggers the fusogenic conformational change in E, at the reduced pH of the endosome. In the fusion loop, Phe-108 adopts a distinct conformation, forming additional trimer contacts and filling the bowl-shaped concavity observed at the tip of the DEN-2 sE trimer.Dengue virus, a member of the flavivirus family, imposes one of the largest social and economic burdens of any mosquitoborne viral pathogen (6, 11). Three structural proteins (C, M, and E) and a lipid bilayer package the positive-strand RNA genomes of flaviviruses (13). The core nucleocapsid protein, C, binds directly to genomic RNA, while the major envelope glycoprotein, E, and the membrane protein, M, form the outer protein shell (9). C-terminal ␣-helical hairpins anchor E and M in the lipid membrane. E binds a receptor on the host cell surface during infection. Receptor binding directs the virion to the endocytic pathway. E responds to the reduced pH of the endosome with a large conformational rearrangement (17). This rearrangement delivers the energy required to bend the host cell membrane toward the viral membrane, inducing the two membranes to fuse (17). The fusogenic conformational rearrangement is a critical step in viral entry, as it delivers the viral genome into the cytoplasm. Crystal structures of the E protein ectodomains from dengue virus type 2 (DEN-2) and from tick-borne encephalitis (TBE) virus have been determined both before and after their fusogenic conformational rearrangements (3,16,17,22,26). The structures of DEN-3 virus E and of West Nile virus E in the prefusion conformation have also been determined (8,18,19). These structures provide us with a detailed molecular picture of the fusion mechanism of flaviviruses (15). First, E inserts a hydrophobic anchor, the so-called fusion loop, into the outer bilayer leaflet of the host cell membrane. Second, E folds back on itself, directing its C-terminal transmembrane anchor toward the fusion loop. This fold-back forces the host cell membrane (held by the fusion loop) and the viral membrane (held by the C-terminal transmembrane anchor) against each other, resulting in fusion of the two membranes. Here we report the crystal structure of a soluble fragment of the E protein (sE) from DEN-1 containing residues 1 to 400, that is, all but the last 50 residues of the ectodomain (Fig. 1). The protein is in the postfusion conformation even though it was never ex...