Adeno-associated virus serotype 2 (AAV-2) is a leading candidate vector for gene therapy. Cell entry starts with attachment to a primary receptor, Heparan Sulfate Proteoglycan (HSPG) before binding to a co-receptor. Here, cryo-electron microscopy provides direct visualization of the virus–HSPG interactions. Single particle analysis was performed on AAV-2 complexed with a 17kDa heparin fragment at 8.3Å resolution. Heparin density covers the shoulder of spikes surrounding viral 3-fold symmetry axes. Previously implicated, positively charged residues R448/585, R451/588 and R350/487 from another subunit cluster at the center of the heparin footprint. The footprint is much more extensive than apparent through mutagenesis, including R347/484, K395/532 and K390/527 that are more conserved, but whose roles have been controversial. It also includes much of a region proposed as a co-receptor site, because prior studies had not revealed heparin interactions. Heparin density bridges over the viral 3-fold axes, indicating multivalent attachment to symmetry-related binding sites.

The use of adeno-associated virus (AAV) as a gene therapy vector is limited by the host neutralizing immune response. The cryo-electron microscopy (EM) structure at 8.5 Å resolution is determined for a complex of AAV-2 with the Fab′ fragment of monoclonal antibody (MAb) A20, the most extensively characterized AAV MAb. The binding footprint is determined through fitting the cryo-EM reconstruction with a homology model following sequencing of the variable domain, and provides a structural basis for integrating diverse prior epitope mappings. The footprint extends from the previously implicated plateau to the side of the spike, and into the conserved canyon, covering a larger area than anticipated. Comparison with structures of binding and non-binding serotypes indicates that recognition depends on a combination of subtle serotype-specific features. Separation of the neutralizing epitope from the heparan sulfate cell attachment site encourages attempts to develop immune-resistant vectors that can still bind to target cells.

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COPII vesicles transport proteins from the ER to the Golgi apparatus. Previous cryoEM structures of the COPII cage lacked the resolution necessary to determine the residues of Sec13 and Sec31 that mediate assembly and flexibility of the COPII cage. Here we present a 12Å-resolution structure of the COPII cage, where the tertiary structure of Sec13 and Sec31 is clearly identifiable. We employ this structure and a homology model of the Sec13-Sec31 complex to create a reliable pseudo-atomic model of the COPII cage. We combined this model with hydrogen/deuterium exchange mass spectrometry analysis to characterize four distinct contact regions at the vertices of the COPII cage. Furthermore, we found that the 2-fold symmetry of the Sec31 dimeric region of Sec13-31 is broken on cage formation, and that the resulting hinge is essential to form the proper edge geometry in COPII cages.

Vaccine manufacturing costs prevent a significant portion of the world's population from accessing protection from vaccinepreventable diseases. To enhance vaccine production at reduced costs, a genome-wide RNA interference (RNAi) screen was performed to identify gene knockdown events that enhanced poliovirus replication. Primary screen hits were validated in a Vero vaccine manufacturing cell line using attenuated and wild-type poliovirus strains. Multiple single and dual gene silencing events increased poliovirus titers >20-fold and >50-fold, respectively. Host gene knockdown events did not affect virus antigenicity, and clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9-mediated knockout of the top candidates dramatically improved viral vaccine strain production. Interestingly, silencing of several genes that enhanced poliovirus replication also enhanced replication of enterovirus 71, a clinically relevant virus to which vaccines are being targeted. The discovery that host gene modulation can markedly increase virus vaccine production dramatically alters mammalian cell-based vaccine manufacturing possibilities and should facilitate polio eradication using the inactivated poliovirus vaccine. IMPORTANCEUsing a genome-wide RNAi screen, a collection of host virus resistance genes was identified that, upon silencing, increased poliovirus and enterovirus 71 production by from 10-fold to >50-fold in a Vero vaccine manufacturing cell line. This report provides novel insights into enterovirus-host interactions and describes an approach to developing the next generation of vaccine manufacturing through engineered vaccine cell lines. The results show that specific gene silencing and knockout events can enhance viral titers of both attenuated (Sabin strain) and wild-type polioviruses, a finding that should greatly facilitate global implementation of inactivated polio vaccine as well as further reduce costs for live-attenuated oral polio vaccines. This work describes a platform-enabling technology applicable to most vaccine-preventable diseases. Vaccines are important defenses in the fight against infectious disease. Currently, a complex set of factors such as population dynamics and bioproduction costs limit the ability to provide adequate immunization coverage to many economically distressed countries. The current efforts to eradicate poliovirus exemplify these challenges. The oral polio vaccine (OPV), consisting of attenuated Sabin strains, has reduced the total number of poliomyelitis cases by Ͼ99% since the late 1980s. However, live attenuated strains carry the risk of phenotypic reversion to a neurovirulent "vaccine-derived poliovirus" (VDPV) capable of inducing vaccine-associated paralytic poliomyelitis (VAPP) (1, 2). To prevent the emergence and circulation of VDPVs during the polio eradication effort and beyond, OPV must be replaced by the inactivated poliovirus vaccine (IPV) (3). The cost of IPV, which is approximately $3.00 per dose compared to approximately $0.20 for OPV, is a major o...

Structural studies have revealed some of the organizing principles and mechanisms involved in the assembly of the COPII coat including the location of the Sec23/24 adapter layer. Previous studies, however, were unable to unambiguously determine the positions of Sec23 and Sec24 in the coat. Here we have determined a cryogenic electron microscopic structure of Sec13/31 together with Sec23. Electron tomography revealed that the binding of Sec23 induces Sec13/31 to form a variety of different geometries including a cuboctahedron, as was previously characterized for Sec13/31 alone. Single particle reconstruction of the Sec13/31-23 cuboctahedra revealed that the binding of Sec23 induces a conformational change in Sec13/31 resulting in a more extended conformation. Docking Sec23 crystal structures into the EM map suggested that Sec24 projects its cargo binding surface out into the large open faces of the coat. These results have implications for the mechanisms by which COPII transports large cargos, cargos with large intracellular domains, and for tethering complexes that must project out of the coat in order to interact with their binding partners. Furthermore, Sec23 binds Sec13/31 at two unique sites in the coat, which suggests that each site may have unique roles in the mechanisms of COPII vesiculation.

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