Human metapneumovirus G protein is highly conserved within but not between genetic lineages.

Human metapneumovirus (HMPV) is an important cause of acute respiratory illnesses in children. HMPV encodes two major surface glycoproteins, fusion (F) and glycoprotein (G). The function of G has not been fully established, though it is dispensable for in vitro and in vivo replication. We analyzed 87 full-length HMPV G sequences from isolates collected over 20 years. The G sequences fell into four subgroups with a mean 63 % amino acid identity (minimum 29 %). The length of G varied from 217 to 241 residues. Structural features such as proline content and N- and O-glycosylation sites were present in all strains but quite variable between subgroups. There was minimal drift within the subgroups over 20 years. The estimated time to the most recent common ancestor was 215 years. HMPV G was conserved within lineages over 20 years, suggesting functional constraints on diversity. However, G was poorly conserved between subgroups, pointing to potentially distinct roles for G among different viral lineages.