Bufavirus strain 1 (BuV1), a member of the Protoparvovirus genus of the Parvoviridae, was first isolated from fecal samples of children with acute diarrhea in Burkina Faso. Since this initial discovery, BuVs have been isolated in several countries, including Finland, the Netherlands, and Bhutan, in pediatric patients exhibiting similar symptoms. Towards their characterization, the structures of virus-like particles of BuV1, BuV2, and BuV3, the current known genotypes, have been determined by cryo-electron microscopy and image reconstruction to 2.84, 3.79, and 3.25 Å, respectively. The BuVs, 65–73% identical in amino acid sequence, conserve the major viral protein, VP2, structure and general capsid surface features of parvoviruses. These include a core β-barrel (βB-βI), α-helix A, and large surface loops inserted between these elements in VP2. The capsid contains depressions at the icosahedral 2-fold and around the 5-fold axes, and has three separated protrusions surrounding the 3-fold axes. Structure comparison among the BuVs and to available parvovirus structures revealed capsid surface variations and capsid 3-fold protrusions that depart from the single pinwheel arrangement of the animal protoparvoviruses. These structures provide a platform to begin the molecular characterization of these potentially pathogenic viruses.

The strikingly high transmissibility and antibody evasion of SARS-CoV-2 Omicron variants have posed great challenges to the efficacy of current vaccines and antibody immunotherapy. Here, we screen 34 BNT162b2-vaccinees and isolate a public broadly neutralizing antibody ZCB11 derived from the IGHV1-58 family. ZCB11 targets viral receptor-binding domain specifically and neutralizes all SARS-CoV-2 variants of concern, especially with great potency against authentic Omicron and Delta variants. Pseudovirus-based mapping of 57 naturally occurred spike mutations or deletions reveals that S371L results in 11-fold neutralization resistance, but it is rescued by compensating mutations in Omicron variants. Cryo-EM analysis demonstrates that ZCB11 heavy chain predominantly interacts with Omicron spike trimer with receptor-binding domain in up conformation blocking ACE2 binding. In addition, prophylactic or therapeutic ZCB11 administration protects lung infection against Omicron viral challenge in golden Syrian hamsters. These results suggest that vaccine-induced ZCB11 is a promising broadly neutralizing antibody for biomedical interventions against pandemic SARS-CoV-2.

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The strikingly high transmissibility and antibody evasion of SARS-CoV-2 Omicron variant have posted great challenges on the efficacy of current vaccines and antibody immunotherapy. Here, we screened 34 BNT162b2-vaccinees and cloned a public broadly neutralizing antibody (bNAb) ZCB11 from an elite vaccinee. ZCB11 neutralized all authentic SARS-CoV-2 variants of concern (VOCs), including Omicron and OmicronR346K with potent IC50 concentrations of 36.8 and 11.7 ng/mL, respectively. Functional analysis demonstrated that ZCB11 targeted viral receptor-binding domain (RBD) and competed strongly with ZB8, a known RBD-specific class II NAb. Pseudovirus-based mapping of 57 naturally occurred single mutations or deletions revealed that only S371L resulted in 11-fold neutralization resistance, but this phenotype was not observed in the Omicron variant. Furthermore, prophylactic ZCB11 administration protected lung infection against both the circulating pandemic Delta and Omicron variants in golden Syrian hamsters. These results demonstrated that vaccine-induced ZCB11 is a promising bNAb for immunotherapy against pandemic SARS-CoV-2 VOCs.

Human bocavirus 1 (HBoV1) and HBoV2-4 infect children and immunocompromised individuals, resulting in respiratory and gastrointestinal infections, respectively. Using cryo-electron microscopy and image reconstruction, the HBoV2 capsid structure was determined to 2.7 Å resolution at pH 7.4 and compared to the previously determined HBoV1, HBoV3, and HBoV4 structures. Consistent with previous findings, surface variable region (VR) III of the capsid protein VP3, proposed as a host tissue-tropism determinant, was structurally similar among the gastrointestinal strains HBoV2-4, but differed from HBoV1 with its tropism for the respiratory tract. Towards understanding the entry and trafficking properties of these viruses, HBoV1 and HBoV2 were further analyzed as species representatives of the two HBoV tropisms. Their cell surface glycan-binding characteristics were analyzed, and capsid structures determined to 2.5-2.7 Å resolution at pH 5.5 and 2.6, conditions normally encountered during infection. The data showed that glycans with terminal sialic acid, galactose, GlcNAc or heparan sulfate moieties do not facilitate HBoV1 or HBoV2 cellular attachment. With respect to trafficking, conformational changes common to both viruses were observed at low pH conditions localized to the VP N-terminus under the 5-fold channel, in the surface loops VR-I and VR-V and specific side-chain residues such as cysteines and histidines. The 5-fold conformational movements provide insight into the potential mechanism of VP N-terminal dynamics during HBoV infection and side-chain modifications highlight pH-sensitive regions of the capsid. IMPORTANCE Human bocaviruses (HBoVs) are associated with disease in humans. However, the lack of an animal model and a versatile cell culture system to study their life cycle limits the ability to develop specific treatments or vaccines. This study presents the structure of HBoV2, at 2.7 Å resolution, determined for comparison to the existing HBoV1, HBoV3, and HBoV4 structures, to enable the molecular characterization of strain and genus-specific capsid features contributing to tissue tropism and antigenicity. Furthermore, HBoV1 and HBoV2 structures determined under acidic conditions provide insight into capsid changes associated with endosomal and gastrointestinal acidification. Structural rearrangements of the capsid VP N-terminus, at the base of the 5-fold channel, demonstrate a disordering of a “basket” motif as pH decreases. These observations begin to unravel the molecular mechanism of HBoV infection and provide information for control strategies.