Conservation of G-Protein Epitopes in Respiratory Syncytial Virus (Group A) Despite Broad Genetic Diversity: Is Antibody Selection Involved in Virus Evolution?

Abstract

Worldwide G-glycoprotein phylogeny of human respiratory syncytial virus (hRSV) group A sequences revealed diversification in major clades and genotypes over more than 50 years of recorded history. Multiple genotypes cocirculated during prolonged periods of time, but recent dominance of the GA2 genotype was noticed in several studies, and it is highlighted here with sequences from viruses circulating recently in Spain and Panama. Reactivity of group A viruses with monoclonal antibodies (MAbs) that recognize strain-variable epitopes of the G glycoprotein failed to correlate genotype diversification with antibody reactivity. Additionally, no clear correlation was found between changes in strain-variable epitopes and predicted sites of positive selection, despite both traits being associated with the C-terminal third of the G glycoprotein. Hence, our data do not lend support to the proposed antibody-driven selection of variants as a major determinant of hRSV evolution. Other alternative mechanisms are considered to account for the high degree of hRSV G-protein variability. H uman respiratory syncytial virus (hRSV) is recognized as the major cause of severe acute lower respiratory tract infections (ALRI) in infants and young children worldwide (1). hRSV causes annual epidemics, and reinfections are common throughout life, although they are usually less severe than the primary infections. hRSV is also an important cause of morbidity and mortality in the elderly and in adults with cardiopulmonary disease or with an impaired immune system (2). IMPORTANCE An unusual characteristic of the G glycoprotein of human respiratory syncytial virus (hRSV) is the accumulation of nonsynonymous (N) changes at higher rates than synonymous (S) changes, reaching dN/dS valueshRSV is an enveloped, nonsegmented, negative-sense RNA virus, classified in the genus Pneumovirus within the Paramyxoviridae family (for a recent review, see reference 3). The hRSV genome encodes 11 proteins, two of them being the major surface glycoproteins of the virus envelope. These are (i) the attachment (G) protein, which mediates binding of the virus to the cell surface (4), and (ii) the fusion (F) protein, which promotes fusion of the virus and cell membrane, allowing cell entry of the viral genome (5).The G protein is a type II glycoprotein synthesized as a 32-kDa polypeptide precursor of 297 to 310 amino acids (aa), depending on the strain, and modified posttranslationally by the addition of several N-linked oligosaccharides and multiple O-linked sugar chains (6). The G-protein ectodomain (from residue 67 to the C terminus) has a central conserved region (aa 163 to 189) that includes four Cys residues (residues 173, 176, 182, and 186), and it is essentially devoid of potential glycosylation sites. This conserved region is flanked by two highly variable mucin-like segments, very rich in Ser and Thr, that are potential sites of O glycosylation. The extensive glycosylation of the G protein shapes its reactivity with both murine monoclonal antibodies (M...

Molecular evolution of the fusion protein gene in human respiratory syncytial virus subgroup A

“…5 the G gene in domestic and/or local areas (Cui et al, 2013;Dapt et al, 2010;Duvvuri et al, 2015;Esposito et al, 2015;Trento et al, 2015). In addition, dominant HRSV infection is caused by HRSV-A rather than HRSV-B (Cui et al, 2013;Esposito et al, 2015).…”

“…To compare the evolution of F and G genes, we also constructed the MCMC tree based on the full-length sequences of the G gene (Trento et al, 2015). To genotype the strains in the MCMC tree constructed using the F gene sequences, we used an MCMC tree based on the G gene sequences.…”

“…To genotype the strains in the MCMC tree constructed using the F gene sequences, we used an MCMC tree based on the G gene sequences. To construct an MCMC tree based on G gene sequences, we collected full-length gene sequences from Genbank, as previously described (Trento et al, 2015) and (Trento et al, 2015). The best substitution model was selected using Kakusan4 (Tanabe, 2011).…”

“…Based on the phylogenetic topology and intergenotypic pairwise distance (p-distance), we assigned each genotype of the present strains as previously described (Trento et al, 2015).…”

“…HRSV-A and -B have been further classified into 12 genotypes (GA1-7, SAA1, NA1, NA2, ON1, and ON2) and 21 genotypes (GB1-4, BA1-11, SAB1-4, and URU1-2), respectively (Cui et al, 2013;Hirano et al, 2014;Nagasawa et al, 2015). However, a recent report suggests that HRSV-A can be classified into seven genotypes (GA1-7; Trento et al, 2015).…”