1.A.90 The Human Metapneumovirus (HMPV) Viroporin (HMPV-viroporin) Family
Human metapneumovirus (HMPV), first identified in 2001, is a causative agent of severe respiratory tract disease worldwide. The SH protein is one of three glycoproteins encoded by all strains of HMPV. These three glycoproteins are the G protein, which plays a role in glycosaminoglycan binding, the
fusion (F) protein, which is necessary and sufficient for both viral binding to the target cell and fusion between the cellular plasma membrane and the viral membrane, and the SH (small hydrophobic) protein, which appears to be a viroporin.
The SH protein of the closely related respiratory syncytial virus may also function as a viroporin, It forms oligomeric structures consistent with a pore and alters membrane permeability. Masante et al. (2014) showed that both the full-length HMPV SH protein and the isolated SH protein transmembrane domain can associate into higher order oligomers. In addition, HMPV SH expression resulted in increases in permeability to hygromycin B and alteration of subcellular localization of a fluorescent dye, indicating that SH affects membrane permeability. These results suggest that the HMPV SH protein has characteristics consistent with those of a viroporin.
Masante et al. (2014) also reported that expression of the HMPV SH protein can significantly decrease HMPV F protein-promoted membrane fusion activity, with the SH extracellular domain and transmembrane domain playing the key role in this inhibition. This suggests that the HMPV SH protein may regulate both membrane permeability and fusion protein function during viral infection.