Studies on protein regulation of virus-mediated membrance fusion

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1.Previosly, we had obtained four escape mutants under pressure of an anti-HN monoclonal antibody (MAb), which inhibited cell fusion induced by human parainfluenza type 2 virus (HPIV2). In the present study, further analyzes have proved that the MAb recognizes 83Asn and 91Lys on the HN molecule.2.The HN and F proteins of three paramyxoviruses (HPIV2, HPIV4, and SV41) were expressed in cells by transfecting them with recombinant plasmid encoding each protein gene. Coexpression of HPIV2 HN with HPIV2 F protein resulted in induction of prominent cell fusion. HPIV2 HN could also promote cell fusion when coexpressed with SV41 F or HPIV4 F proteins, although at lower extents. SV41 HN or HPIV4 HN did not induce cell fusion by coexpressing with HPIV2 F protein.3.Based on the above observation, futher analyzes were performed by constructing and expressing 32 chimeric proteins of HPIV2 HN and SV41 HN proteins. It was revealed that two regions on the HPIV2 HN protein ranging from 37Ser to 91Ser (region A) and ranging from 148Gly to 20Ala (region B) are involved in functional molecular interaction with the F protein, which is a prerequiste for cell fusion induction. On the other hand, similar analyzes of chimeric F proteins have indicated that two regions on HPIV2 F protein ranging from 128Ala to 227Ala (region Y) and from 430Tur to 551Ser (region Z) are involved in the functional interaction with the HN protein.4.These results suggest that molecular interaction between HN and F proteins are indispensable for cell fusion, and each protein has two regions which are involed in the interaction. It is notewothy that one of the two regions of each protein includes the transmembrane domains which may be in close proximity to the fusion site.