Characterization of a key residue for hyperfusogenic phenotype in human parainfluenza virus type 2 (hPIV-2) fusion glycoprotein

Mutations in the fusion protein heptad repeat domains of human metapneumovirus impact on the formation of syncytia

Human metapneumovirus (HMPV) is an important cause of respiratory tract infections. The mechanism by which its fusion (F) protein is responsible for variable cytopathic effects in vitro remains unknown. We aligned the F sequences of the poorly fusogenic B2/CAN98-75 strain and the hyperfusogenic A1/C-85473 strain and identified divergent residues located in the two functional heptad repeats domains (HRA and HRB). We generated recombinant viruses by inserting the mutations N135T-G139N-T143K-K166E-E167D in HRA and/or K479R-N482S in HRB, corresponding to swapped sequences from C-85473, into CAN98-75 background and investigated their impact on in vitro phenotype and fusogenicity. We demonstrated that the five HRA mutations enhanced the fusogenicity of the recombinant rCAN98-75 virus, almost restoring the phenotype of the wild-type rC-85473 strain, whereas HRB substitutions alone had no significant effect on cell-cell fusion. Altogether, our results support the importance of the HRA domain for an HMPV-triggered fusion mechanism and identify key residues that modulate syncytium formation.

Genetic diversity among human parainfluenza virus type 2 isolated in Croatia between 2011 and 2014

The dynamics and evolution of the human parainfluenza virus type 2 (HPIV2) in Croatia, and also globally, are largely unknown. Most HPIV2 infections are treated symptomatically outside the hospital setting. Thus, the diagnosis is missing making it difficult to follow the genetic variation and evolution of the HPIV2. This study explores hospitalized HPIV2 cases in Croatia during 4-year period (2011-2014). Most cases in this period were reported in October or November (68.75%) and most of patients were under 2 years of age (81.25%). For molecular analyses, we used the F and HN gene sequences and showed that although both regions are equally suitable for phylogenetic analyses it would be advantageous to use regions longer than 2 kb for HPIV2 analyses of isolates which are spatially and temporally closely related. We show here that the dominant cluster in this area was cluster G3 while only one strain isolated in this period was positioned in the distant cluster G1a. Further monitoring of the HPIV2 will determine whether cluster G3 will remain dominant or it will be overruled by cluster G1a. This will be important for the surveillance of virus circulation in population and significance of the viral infection. J. Med. Virol. 88:1733-1741, 2016. © 2016 Wiley Periodicals, Inc.