Sequence polymorphism of the predicted human metapneumovirus G glycoprotein

Abstract

The putative G glycoprotein genes of 25 human metapneumovirus (hMPV) field isolates obtained during five consecutive epidemic seasons (1997 to 2002) were sequenced. Sequence alignments identified two major genetic groups, designated groups 1 and 2, and two minor genetic clusters within each major group, designated subgroups A and B. Extensive nucleotide and deduced amino acid sequence variability was observed, consisting of high rates of nucleotide substitutions, use of alternative transcription-termination codons and insertions that retained the reading frame. Deduced amino acid sequences showed the greatest variability, with most differences located in the extracellular domain of the protein: nucleotide and amino acid sequence identities for the entire open reading frame ranged from 52 to 58 % and 31 to 35 %, respectively, between the two major groups. Like the closely related avian pneumovirus and human and bovine respiratory syncytial viruses, the predicted G protein of hMPV shared the basic features of a type II mucin-like glycosylated protein. However, differences from these related viruses were also observed, e.g. lack of conserved cysteine clusters as seen in human respiratory syncytial virus and avian pneumovirus. The displacement of genetic groups of hMPV observed during the study period suggests that potential antigenic differences in the G glycoprotein, which have evolved in response to immune-mediated pressure, may influence the circulation patterns of hMPV strains. INTRODUCTIONHuman metapneumovirus (hMPV), a recently recognized paramyxovirus (van den Hoogen et al., 2001), has been linked to acute respiratory illness in children, the elderly and the immunocompromised Jartii et al., 2002;Pelletier et al., 2002;Peret et al., 2002;Stockton et al., 2002;Falsey et al., 2003;. Like human respiratory syncytial virus (HRSV), hMPV appears to be ubiquitous, infecting most children at an early age, and exhibits a distinct annual epidemic peak in the winter months (Falsey et al., 2003).hMPV has been tentatively assigned to the genus Metapneumovirus (van den Hoogen et al., 2001Hoogen et al., , 2002 based upon sequence identity and similar genomic organization to avian pneumovirus (APV). Analyses of hMPV and APV sequences have shown that hMPV shares the closest relationship with APV type C (van den Hoogen et al., 2002; Bastien et al., 2003). hMPV, along with APV, HRSV and bovine respiratory syncytial virus (BRSV), belongs to the family Paramyxoviridae, subfamily Pneumovirinae, whose members encode the G protein, a type II mucinlike glycoprotein. The G glycoprotein of HRSV induces a group-specific protective immune response and is associated with enhanced HRSV disease (Sparer et al., 1998; Tripp et al., 2001). The G glycoproteins of HRSV and BRSV also participate but do not seem to be essential in virus attachment (Teng et al., 2002;Schlender et al., 2003).The genetic variability of the hMPV G gene has not been fully examined, although limited studies have identified two major lineages of hMPV van den Hoogen e...

Human Metapneumovirus Genetic Variability, South Africa

“…The sequence variation in the G gene was due to nucleotide substitutions, in-frame insertions, and the use of alternative termination transcription codons. The in-frame insertions we observed suggest that the nucleotide changes previously seen (17) were not due to the passage of hMPV in cell culture. Structural features of the G protein for both groups of South African strains were similar to those observed by others (17,19) with a high serine-threonine content (31%–36%) and variable numbers and positions of N-linked glycosylation sites.…”

“…The in-frame insertions we observed suggest that the nucleotide changes previously seen (17) were not due to the passage of hMPV in cell culture. Structural features of the G protein for both groups of South African strains were similar to those observed by others (17,19) with a high serine-threonine content (31%–36%) and variable numbers and positions of N-linked glycosylation sites. The N-linked glycosylation site at the junction between the intracellular and transmembrane domains (position 30–32) was the only conserved site among all groups.…”

“…We also only observed 1 conserved cysteine residue in the intracellular domain, at amino acid position 27 of the G gene. The second cysteine residue in the extracellular domain, at position 65, previously reported to be present in all group B isolates (17), was absent from 2 South African group B isolates. Hydrophobicity plot data (data not shown) were also similar for both groups A and B, and as reported by others (17,19).…”

“…This variability poses a challenge for future vaccine development that relies on worldwide molecular epidemiologic studies. Recently, the hMPV G gene was shown to be highly variable, particularly in the extracellular domain, as a result of nucleotide substitutions, insertions, and the use of alternative termination transcription codons (17–19). Limited data have also indicated that the 2 groups of hMPV cocirculate and that different subgroups may predominate from year to year (2,4,17,21).…”

“…Limited available data indicate that both groups can circulate in a single season with the possibility of the predominant group switching in successive seasons (2,4,17,21). Genetic variation in the hMPV attachment glycoprotein (G protein) indicates a high degree of nucleotide variation, which results in amino acid changes (17–19). This sequence variation within the hMPV G gene has been postulated to be due to immunologic pressure.…”