Identification of Amino Acid Substitutions with Compensational Effects in the Attachment Protein of Canine Distemper Virus

Abstract

The hemagglutinin (H) gene of canine distemper virus (CDV) encodes the receptor-binding protein. This protein, together with the fusion (F) protein, is pivotal for infectivity since it contributes to the fusion of the viral envelope with the host cell membrane. Of the two receptors currently known for CDV (nectin-4 and the signaling lymphocyte activation molecule [SLAM]), SLAM is considered the most relevant for host susceptibility. To investigate how evolution might have impacted the host-CDV interaction, we examined the functional properties of a series of missense single nucleotide polymorphisms (SNPs) naturally accumulating within the H-gene sequences during the transition between two distinct but related strains. The two strains, a wild-type strain and a consensus strain, were part of a single continental outbreak in European wildlife and occurred in distinct geographical areas 2 years apart. The deduced amino acid sequence of the two H genes differed at 5 residues. A panel of mutants carrying all the combinations of the SNPs was obtained by site-directed mutagenesis. The selected mutant, wild type, and consensus H proteins were functionally evaluated according to their surface expression, SLAM binding, fusion protein interaction, and cell fusion efficiencies. The results highlight that the most detrimental functional effects are associated with specific sets of SNPs. Strikingly, an efficient compensational system driven by additional SNPs appears to come into play, virtually neutralizing the negative functional effects. This system seems to contribute to the maintenance of the tightly regulated function of the Hgene-encoded attachment protein. IMPORTANCETo investigate how evolution might have impacted the host-canine distemper virus (CDV) interaction, we examined the functional properties of naturally occurring single nucleotide polymorphisms (SNPs) in the hemagglutinin gene of two related but distinct strains of CDV. The hemagglutinin gene encodes the attachment protein, which is pivotal for infection. Our results show that few SNPs have a relevant detrimental impact and they generally appear in specific combinations (molecular signatures). These drastic negative changes are neutralized by compensatory mutations, which contribute to maintenance of an overall constant bioactivity of the attachment protein. This compensational mechanism might reflect the reaction of the CDV machinery to the changes occurring in the virus following antigenic variations critical for virulence.

Canine Distemper Virus Spread and Transmission to Naive Ferrets: Selective Pressure on Signaling Lymphocyte Activation Molecule-Dependent Entry

“…Some South African isolates have an M195I substitution (49) located close to the T192A mutation in our SLAMrev virus. A different substitution at this position (M195V) may influence receptor binding (39). Many isolates of the Asia-I lineage have a Y549H substitution (50), which is immediately adjacent to residues 547/548 mutated in the SLAM-blind virus.…”

“…The two phases of CDV infection and disease, colonization of immune tissues and spread to epithelia, are determined by interaction with the two receptors SLAM and nectin-4, respectively (37,38). Evolutionary forces drive H protein variability during virus circulation, and compensatory mutations often arise at other positions that offset detrimental changes in the protein (39). By infecting susceptible animals with viruses that are no longer able to interact with either SLAM or nectin-4 (26, 27), we can gain insight into the compensatory mechanisms that affect the interactions between CDV and its receptors.…”

Mediterranean Fin Whales (Balaenoptera physalus) Threatened by Dolphin MorbilliVirus

“…Recent studies showed that similar amino acid changes could affect virulence and infectivity of different Canine distemper virus (family Paramyxoviridae , genus Morbillivirus ) strains, but such changes are often neutralized by compensatory mutations that preserve the biologic activity of H protein ( 15 ). Furthermore, despite the high sequence homology observed between N, P, and H genes of the DMV strain identified in the newborn fin whale in our study and in the isolates recovered from DMV-affected cetaceans during the 1990–1992 and the 2006–2007 epidemics (GenBank accession no.…”

Mediterranean Fin Whales (Balaenoptera physalus) Threatened by Dolphin MorbilliVirus

“…Although the single amino acid substitution, p.Ala451Thr, did not cause substantial variations in the structure of H antigen, the effect of the variation on protein functions is unclear. Recent studies showed that similar amino acid changes could affect virulence and infectivity of different Canine distemper virus (family Paramyxoviridae , genus Morbillivirus ) strains, but such changes are often neutralized by compensatory mutations that preserve the biologic activity of H protein ( 15 ). Furthermore, despite the high sequence homology observed between N, P, and H genes of the DMV strain identified in the newborn fin whale in our study and in the isolates recovered from DMV-affected cetaceans during the 1990–1992 and the 2006–2007 epidemics (GenBank accession no.…”