The recently identified human metapneumovirus (HMPV) is a worldwide respiratory virus affecting all age groups and causing pneumonia and bronchiolitis in severe cases. that a positive charge at position 435 is required but not sufficient for F-mediated membrane fusion. Arginine or lysine substitution at position 435 resulted in a hyperfusogenic F protein while substitute with aspartate or glutamate abolished fusion activity. Research with recombinant infections carrying mutations in this area verified its importance. Furthermore another region inside the F2 area identified as getting rich in billed residues was discovered to modulate fusion activity of HMPV F. Lack of charge at residues E51 D54 and E56 changed regional folding and general stability from the F proteins with dramatic outcomes for fusion activity. All together these research implicate billed residues and potential electrostatic connections in function pH sensing and general balance of HMPV F. Launch Individual metapneumovirus (HMPV) is certainly a recently uncovered paramyxovirus that is clearly a major reason behind higher and lower respiratory system disease worldwide in every age ranges (8 9 28 41 Numerous studies have shown that in addition to exacerbating underlying diseases such as chronic obstructive pulmonary disease (COPD) HMPV can cause significant morbidity and some mortality especially in infants the elderly and people with compromised immune systems (8 15 16 Indeed studies have estimated that HMPV is the second or third most common cause of severe acute respiratory tract infection in children (28). Despite its widespread human pathogenicity there is currently no approved antiviral medication or vaccine against HMPV. HMPV expresses three surface glycoproteins: the putative attachment protein (G) the fusion protein (F) and the small hydrophobic protein (SH) (25). The F proteins of paramyxoviruses including that of HMPV are trimeric type I fusion proteins. The membrane fusion event is usually intimately linked to final formation of a six-helix bundle in the F protein after extensive conformational changes bring two heptad repeat (HR) regions-HRA and HRB-into close proximity (37). For paramyxoviruses the triggering event that drives these conformational changes is hypothesized to occur following attachment of the computer virus to its receptor. This triggering must be regulated VX-680 carefully as the subsequent conformational change of the F protein from its metastable prefusion form to its stable postfusion form is usually irreversible. Before a paramyxovirus F protein can be brought on to promote membrane fusion it must undergo one or more proteolytic cleavage events which cut the precursor form of the protein (F0) into an active disulfide-linked form (F1+F2) (25 37 Unlike most paramyxovirus F proteins which are processed by proteases present in the host VX-680 cell HMPV F requires exogenous protease cleavage to VX-680 be fusogenically active. Thus for contamination to occur HMPV requires proteolytic activation after budding. when devoid of the G protein (7 23 25 However unlike RSV HMPV lacking the G protein is also infectious in animals including nonhuman primates (3 7 Additionally the HMPV F protein alone is able to promote cell-cell fusion in the absence of the G protein (35). These observations suggest that HMPV F can promote both attachment and efficient membrane fusion. Another distinguishing feature of HMPV is usually that for at least some strains of the computer virus low pH can trigger the fusion activity of the F protein (19 35 while most paramyxovirus F proteins are brought on at neutral pH (25). Our laboratory has shown that low-pH treatment of Vero cells transfected with the F protein of HMPV strain CAN97-83 (clade A2) leads to F triggering and subsequent syncytium formation (35). Furthermore inhibitors of endosomal acidification such as bafilomycin A and concanamycin were able Rabbit Polyclonal to Caspase 3 (p17, Cleaved-Asp175). to confer partial protection against infection with a recombinant green fluorescent protein (GFP)-expressing HMPV CAN97-83 strain as well as a B1 strain of the computer virus (27 34 Certain strains of HMPV clade A1 also show VX-680 low-pH-promoted fusion (19). While low-pH triggering is certainly uncommon for paramyxoviruses many viruses from various other pathogen families need low pH for membrane fusion. A vintage example of a sort I fusion proteins brought about by low pH is certainly influenza pathogen hemagglutinin (HA) that includes a triggering threshold of around pH 5.4 (30). Mechanistically it really is believed that electrostatic repulsive makes that occur between residues that become protonated at low pH and their neighboring residues.