Single-Particle Tracking Shows that a Point Mutation in the Carnivore Parvovirus Capsid Switches Binding between Host-Specific Transferrin Receptors

Abstract

bDetermining how viruses infect new hosts via receptor-binding mechanisms is important for understanding virus emergence. We studied the binding kinetics of canine parvovirus (CPV) variants isolated from raccoons-a newly recognized CPV host-to different carnivore transferrin receptors (TfRs) using single-particle tracking. Our data suggest that CPV may utilize adhesion-strengthening mechanisms during TfR binding and that a single mutation in the viral capsid at VP2 position 300 can profoundly alter receptor binding and infectivity. Canine parvovirus (CPV) is a pathogen of dogs that emerged and caused a pandemic of disease in the 1970s and is Ͼ99% identical in nucleotide sequence to feline panleukopenia virus (FPV), a parvovirus that infects cats and other carnivore hosts but not dogs (1-3). Although the emergence of CPV has been presumed to be the result of a direct transfer of FPV or a similar virus from domestic cats to dogs, we recently demonstrated that CPV exists endemically in sylvatic cycles in North America involving a number of wild carnivore hosts, most notably raccoons (4, 5). These recent findings, along with the lack of isolation or detection of intermediate viruses between FPV and CPV from domestic animals, suggest that parvoviruses transfer frequently between domestic and wild carnivores and that the events preceding the pandemic emergence of CPV were more complex than previously believed (6).Although raccoons have long been known to be susceptible to FPV infection (7), they have only recently been identified as an important host for viruses that are closely related to CPV (4, 8). While CPVs from dogs, wolves, and coyotes all contain a Gly at capsid (VP2) position 300, CPVs from raccoons contain an Asp at that position, suggesting that this mutation is important for the adaptation of CPV to raccoons and possibly other wild carnivore hosts (4, 6). Additionally, VP2 position 300 is the most variable residue in the capsid (9-11). Since FPV and CPV capsids can bind to the transferrin receptor type 1 (TfR), in part by involving the structural region surrounding VP2 position 300 (12), the variations observed at this position appear to be selected by the unique TfR structures of individual carnivore hosts. To examine this phenomenon and to better understand the receptor-binding mechanisms involved, we used single-particle tracking (SPT) techniques to characterize the binding of raccoon-derived CPVs, containing either a 300-Asp or 300-Gly VP2 residue, to dog and raccoon TfRs.The virus studied here was the prototype CPV isolated from raccoons (CPV/Raccoon/VA/118-A/07, GenBank sequence accession number JN867610), which contains an Asp at VP2 position 300 and cannot be propagated in dog cells (4, 6). We refer to this virus as Rac118-300D. However, a single point mutation of the VP2 300-Asp (codon GAT) to a Gly (codon GGT) results in efficient dog cell infec- Citation Lee DW, Allison AB, Bacon KB, Parrish CR, Daniel S. 2016. Single-particle tracking shows that a point mutation in the carnivore parvovirus caps...

Parvovirus Capsid Structures Required for Infection: Mutations Controlling Receptor Recognition and Protease Cleavages

“…Because the dissociation curves here did not fit the basic 1:1 binding model, we used the adhesion-strengthening model (43,57). This model assumes that the binding force can change with contact time, perhaps due to bindingtriggered conformational changes of the capsid (43). However, the initial adhesionstrengthening model applies only to studies where contact times for each capsid particle can be measured, whereas here, we measured the collective loss of many capsids from the surface over time.…”

“…Characterizing the dissociation curves can also be useful for determining if adhesion-strengthening mechanisms are present, as demonstrated by related work on tracking contact times between individual parvoviruses and TfRs (43). Because the dissociation curves here did not fit the basic 1:1 binding model, we used the adhesion-strengthening model (43,57).…”

“…The mutation Ala300Asp has been observed repeatedly after natural transfer of CPV-2 from dogs to raccoons or during passage of CPV strains in raccoon cells (40), and the change also arose (along with a change of residue 301) during CPV-2 passage in feline cells in vitro (41,42). The presence of 300Asp also results in reduced canine in vivo and in vitro infection and in decreased binding to the feline TfR (43)(44)(45). The 300Asp substitution results in more extensive structural changes in the capsid than are seen for 300Ala or Gly, due to the formation of a salt bridge between VP2 Asp300 and Arg81 on adjacent subunits, which stabilizes the extended loop that contains residue 300 in a new position (44).…”

Single Virion Tracking Microscopy for the Study of Virus Entry Processes in Live Cells and Biomimetic Platforms

“…Such studies can reveal changes in binding behavior that promote viral attachment. For example, both influenza and canine parvovirus undergo "adhesion-strengthening" where the longer a virion is bound, the more strongly it adheres to the bilayer [37,85]. Overall, these platforms are convenient for gathering insight on this critical virus entry step and how it depends on the host cell surface.…”

“…The importance of studying the binding step is that the tropism of a virus is strongly tied to its ability to bind various receptors. A nice example, illustrating the power of combining single virion binding measurements with cell infectivity studies, clearly showed that a single mutation in the canine parvovirus capsid is able to alter binding to dog and raccoon transferrin receptors and completely change the tropism of the virus [85].…”