Cloning, Expression and Structural Characterization of Human Metapneumovirus Fusion Glycoprotein
Paramyxovirus fusion glycoproteins mediate virus envelope and cell membrane fusion during viral entry. Fusion proteins are type I glycoproteins that exist as trimers with two 4-3 heptad repeat domains that form coiled coil á-helices. A series of conformational changes in this á-helical fusion core brings the viral and target membrane into close proximity making the membrane fusion possible. Human metapneumovirus (hMPV) is a recently discovered Paramyxovirus, which causes upper and lower respiratory tract infection in infants, young children, elderly and immunocompromised patients worldwide. This work concentrates on the structural characterization of the human metapneumovirus fusion (F) glycoprotein. We successfully expressed a recombinant fusion protein ectodomain in mammalian cells and purified it with affinity chromatography. The native protein forms oligomers under native conditions, separating into monomers under denaturing conditions. It shows dominant á-helical secondary structure and retains important antigenic epitopes of neutralizing monoclonal antibodies. Cotton rats immunized with this fusion protein construct have high level of serum neutralizing antibody titer and are protected against hMPV infection. The hMPV F protein likely engages cell surface receptors to mediate attachment and entry.