Complex and Dynamic Interactions between Parvovirus Capsids, Transferrin Receptors, and Antibodies Control Cell Infection and Host Range

Abstract

Antibody and receptor binding are key virus/host interactions that control host range and determine the success of infection. Canine and feline parvovirus capsids bind the transferrin receptor type-1 (TfR) to enter host cells, and specific structural interactions appear necessary to prepare the stable capsids for infection. Here we define the details of binding, competition, and occupancy of wild-type and mutant parvovirus capsids with purified receptors and antibodies. TfR/capsid binding interactions depended on the TfR species and varied widely, with no direct relationship between binding affinity and infection. Capsids bound feline, raccoon, and black-backed jackal TfRs at high affinity, but barely bound canine TfRs, which mediated infection efficiently. TfRs from different species also occupied capsids to different levels, with an estimated 1-2 feline TfRs but 12 black-backed jackal TfRs binding each capsid. Multiple alanine substitutions within loop 1 on the capsid surface reduced TfR binding, but substitutions within loop 3 did not, suggesting that loop 1 directly engaged the TfR and loop 3 sterically affected that interaction. Binding and competition between different TfRs and/or antibodies showed complex relationships. Both antibodies 14 and E competed capsids off TfRs, but antibody E could also compete capsids off itself and antibody 14, likely by inducing capsid structural changes. In some cases, the initial TfR or antibody binding event affected subsequent TfR binding, suggesting that capsid structure changes occur after TfR or antibody binding and may impact infection. This shows that precise, host-specific TfR/capsid interactions, beyond simple attachment, are important for successful infection. Host receptor binding is a key step during viral infection, and may control both infection and host range. In addition to binding, some viruses require specific interactions with host receptors in order to infect, and anti-capsid antibodies can potentially disrupt these interactions, leading to neutralization. Here, we examine the interactions between parvovirus capsids, the receptors from different hosts, and anti-capsid antibodies. We show that interactions between parvovirus capsids and host-specific TfRs vary in both affinity and in the numbers of receptors bound, with complex effects on infection. In addition, antibodies binding to two sites on the capsids had different effects on TfR/capsid binding. These experiments confirm that receptor and antibody binding to parvovirus capsids are complex processes and the infection outcome is not determined simply by the affinity of attachment.

Transferrin receptor binds virus capsid with dynamic motion

“…The consistent interactions provided a pivot point, while the variable interactions supported the dynamic interaction, which resulted in the rock-and-roll motion of the 2 molecules. It should be noted that multiple alanine substitutions within the BC and GH loops of CPV, including some involved in consistent interactions (M87 and T301), did not cause loss of binding affinity to the bbj-TfR (36). Although the CPV residues responsible for binding the bbj-TfR are not known, the tolerance of the Ala substitutions provides useful information.…”

“…Flexibility Induced by Receptor Binding. Previous work and the likely steric interference of bound adjacent TfR molecules suggested no more than 12 copies of the receptor bind per capsid (17,36). Thus, the aim of this work was to solve an asymmetric reconstruction of complex.…”

“…Notably, TfR from bbj (Canis mesomelas) (bbj-TfR) is evolutionarily close to the canine TfR (98.6% amino acid sequence identity), but lacks the glycosylation site on residue 384. Bbj-TfR also binds CPV capsids, with both higher binding affinity and occupancy compared to the canine TfR (36). Thus, the CPV and bbj-TfR complex provides an ideal model for studying the molecular interactions between virus and receptor to understand how TfR binding controls viral host range.…”

“…The interactions between CPV and TfR are intricate, as there appears to be no direct relationship between the affinity of TfR binding and the success of the infection; indeed, some receptor mutants bind with high affinity but do not mediate infection, whereas the binding of the infection-competent canine TfR has very low affinity (36,37). The capsids only engage 1 or a small number of TfRs on the surface of feline cells and also bind only small numbers of receptors when capsids are mixed with purified feline TfRs (17,36).…”

“…The interactions between CPV and TfR are intricate, as there appears to be no direct relationship between the affinity of TfR binding and the success of the infection; indeed, some receptor mutants bind with high affinity but do not mediate infection, whereas the binding of the infection-competent canine TfR has very low affinity (36,37). The capsids only engage 1 or a small number of TfRs on the surface of feline cells and also bind only small numbers of receptors when capsids are mixed with purified feline TfRs (17,36). In the previous cryo-EM study using CPV and feline TfR, we predicted steric interference between adjacent TfR molecules and examined the TfR footprint as well as its binding mode, but precise interpretation was limited due to the low resolution of the asymmetric complex map that was possible at that time (17).…”