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Parvovirus B19 (B19V) is a small non-enveloped virus and known as the causative agent for the mild childhood disease erythema infectiosum. B19V has an extraordinary narrow tissue tropism, showing only productive infection in erythroid precursor cells in the bone marrow. We recently found that the viral protein 1 unique region (VP1u) contains an N-terminal receptor-binding domain (RBD), which mediates the uptake of the virus into cells of the erythroid lineage. To further investigate the role of the RBD in connection with a B19V-unrelated capsid, we chemically coupled the VP1u of B19V to the bacteriophage MS2 capsid and tested the internalization capacity of the bioconjugate on permissive cells. In comparison, we studied the cellular uptake and infection of B19V along the erythroid differentiation. The results showed that the MS2-VP1u bioconjugate mimicked the specific internalization of the native B19V into erythroid precursor cells, which further coincides with the restricted infection profile. The successful mimicry of B19V uptake demonstrates that the RBD in the VP1u is sufficient for the endocytosis of the viral capsid. Furthermore, the recombinant VP1u competed with B19V uptake into permissive cells, thus excluding a significant alternative uptake mechanism by other receptors. Strikingly, the VP1u receptor appeared to be expressed only on erythropoietin-dependent erythroid differentiation stages that also provide the necessary intracellular factors for a productive infection. Taken together, these findings suggest that the VP1u binds to a yet-unknown erythroid-specific cellular receptor and thus restricts the virus entry to permissive cells. [ABSTRACT FROM AUTHOR]

Parvovirus B19 (B19V) is known as the human pathogen causing the mild childhood disease erythema infectiosum. B19V shows an extraordinary narrow tissue tropism for erythroid progenitor cells in the bone marrow, which is determined by a highly restricted uptake. We have previously shown that the specific internalization is mediated by the interaction of the viral protein 1 unique region (VP1u) with a yet unknown cellular receptor. To locate the receptor-binding domain (RBD) within the VP1u, we analyzed the effect of truncations and mutations on the internalization capacity of the recombinant protein into UT7/Epo cells. Here we report that the N-terminal amino acids 5-80 of the VP1u are necessary and sufficient for cellular binding and internalization; thus, this N-terminal region represents the RBD required for B19V uptake. Using site-directed mutagenesis, we further identified a cluster of important amino acids playing a critical role in VP1u internalization. In silico predictions and experimental results suggest that the RBD is structured as a rigid fold of three -helices. Finally, we found that dimerization of the VP1u leads to a considerably enhanced cellular binding and internalization. Taken together, we identified the RBD that mediates B19V uptake and mapped functional and structural motifs within this sequence. The findings reveal insights into the uptake process of B19V, which contribute to understand the pathogenesis of the infection and the neutralization of the virus by the immune system. [ABSTRACT FROM AUTHOR]

Parvovirus B19 (B19V) is a human pathogen with a marked tropism for erythroid progenitor cells (EPCs). The N-terminal of the VP1 unique region (VP1u) contains a receptor-binding domain (RBD), which mediates virus uptake through interaction with an as-yet-unknown receptor (VP1uR). Considering the central role of VP1uR in the virus tropism, we sought to investigate its expression profile in multiple cell types. To this end, we established a PP7 bacteriophage-VP1u bioconjugate, sharing the size and VP1u composition of native B19V capsids. The suitability of the PP7-VP1u construct as a specific and sensitive VP1uR expression marker was validated in competition assays with B19V and recombinant VP1u. VP1uR expression was exclusively detected in erythroid cells and cells reprogrammed towards the erythroid lineage. Sequence alignment and in silico protein structure prediction of the N-terminal of VP1u (N-VP1u) from B19V and other primate erythroparvoviruses (simian, rhesus, and pig-tailed) revealed a similar structure characterized by a fold of three or four α-helices. Functional studies with simian parvovirus confirmed the presence of a conserved RBD in the N-VP1u, mediating virus internalization into human erythroid cells. In summary, this study confirms the exclusive association of VP1uR expression with cells of the erythroid lineage. The presence of an analogous RBD in the VP1u from non-human primate erythroparvoviruses emphasizes their parallel evolutionary trait and zoonotic potential. [ABSTRACT FROM AUTHOR]