Citations

Emergence of epidemic viruses in new hosts threatens both human and other animal populations, and often involves virus evolution to overcome barriers that normally prevent efficient infection and spread in that host. After transfer the separated viruses will evolve in parallel as they spread within the original and new hosts. Here we examine the details of a virus involved in such a host-jumping event, where we define the natural evolution of feline panleukopenia virus (FPV) over 60 y, clarify the origins of the new pandemic canine parvovirus (CPV) that arose in the 1970s, and compare the separate evolution of those viruses over 47 y in cats or dogs. Several live-attenuated FPV vaccine viruses originated from early-1960s isolates or were a recombinant of an early virus, and many sequences in databases proved to be vaccine-derived. The sequences of wild viruses showed that FPV-like strains evolved at less than one-third the rate observed for CPV in dogs, and the higher rate of CPV evolution has been consistent since 1979, when a genetic variant became widespread. The common ancestor of the CPV lineage was related to FPVs from Europe and contained several unique host-adaptive capsid changes associated with canine transferrin receptor type-1 binding. Although the FPV vaccine strains are around 60 y old, little selection for antigenic variation was observed. The distinct evolutionary patterns of these closely related viruses circulating for decades in different hosts emphasize the complex evolution associated with viral epidemic emergence and spread in endemic and new hosts.

Summary Human parvovirus B19 (B19V) exhibits a strict tropism for erythroid progenitor cells, which is governed by the VP1 unique region (VP1u). This region mediates cell-specific uptake by interacting with an unknown cellular receptor, termed VP1uR. Proximity labeling in permissive erythroid cells identified transferrin receptor 1 (TfR1/CD71) as the predominant membrane protein associated with VP1u. VP1u constructs colocalized with TfR1 at the cell surface of erythroid cells. Incubation with anti-TfR1 antibody OKT9 abolished binding and uptake of recombinant VP1u. While OKT9 efficiently inhibited B19V uptake and infection, it did not block virus binding to host cells. Direct binding assays confirmed interaction of VP1u to human TfR1. Using cryoEM we solved the 2.4 Å structure of the TfR1-VP1u complex, mapping the binding site and identifying the specific interactions. These findings establish TfR1 as the previously unknown receptor, VP1uR, required for B19V uptake.

Abstract Cfr methylates C 8 of adenosine 2503 (A2503) in 23 S ribosomal RNA (rRNA) and will also methylate C 2 of A2503 after methylating C 8 . C 8 methylation confers resistance to more than five classes of clinically used antibiotics, highlighting it as a worrisome mechanism of antibiotic resistance. Here, we report the structure of Cfr, determined by cryogenic electron microscopy (Cryo-EM). Despite its small size (∼36 kDa), we exploit a transient protein–RNA crosslink that forms during catalysis, which requires Cys105 to resolve. Using a Cfr Cys105Ala variant and an 87-nucleotide strand of rRNA, we isolate the crosslinked species and determine its structure to 3.0 Å resolution. Notably, the 87-mer rRNA adopts an L-shaped conformation characteristic of tRNAs, rather than the conformation it assumes in the ribosome. One Sentence Summary Cryo-EM structure of Cfr, a radical S-adenosylmethionine methylase that confers antibiotic resistance

Powassan virus (POWV) is an emerging tick-borne flavivirus for which no vaccine or antiviral treatment exists. The incidence of human infections of POWV in North America has been increasing because of the expanding distribution of the tick vector Ixodes scapularis that transmits POWV to humans. To mitigate the dangers of handling a risk group 3 human pathogen, a chimeric virus was constructed from the genetic backbone of a yellow fever virus vaccine strain 17D (YFV-17D) and the external structural proteins of POWV lineage II. The chimera had a comparable phenotype as POWV. The atomic resolution of yellow fever virus-Powassan virus chimera (yPOWV) structure was built without ambiguity, revealing surface glycans and lipid pocket factors. The similarity to other flavivirus structures and the phenotype similar to YFV-17D suggest that there could be future potential as a vaccine candidate.

Host antibody responses are key components in the protection of animals against pathogens, yet the defining properties of viral antigens and induction of B cell responses that result in varied protection are still poorly understood. Parvoviruses are simple molecular structures that display 60 repeated motifs on their capsid surface, and rapidly induce strong antibody responses that protect animals from infection. We recently showed that following canine parvovirus infection of its natural host, the polyclonal response in the sera contained only two or three dominant antibodies that bound two epitopes on the capsid. Here, we characterize key antibodies present in that immune response, identifying their sequences, defining their binding properties on the capsid by cryoelectron microscopic (cryoEM) analysis, and testing their effects on viral infectivity. Two antibodies sharing the same heavy chain bound to the side of the capsid threefold spike (B-site), while another distinct antibody bound close to the threefold axis (A-site). The epitopes of these antibodies overlapped the binding site of the host receptor, the transferrin receptor type-1, but to varying degrees. The antibodies varied widely in their neutralization efficiencies as either immunoglobulins (IgGs) or monomeric antigen-binding fragments (Fabs), which was consistent with their ability to compete for the receptor. The monoclonal antibodies characterized here matched the structures from the cryoEM analysis of polyclonal sera, including those present in a different dog than the monoclonal source. This shows that after infection, a focused response to the viral antigen is produced that protects against infection.