| Research Abstract |
1. Chimeric analysis of the F proteins of human parainfluenza virus type 2 (PIV2) and simian virus 41 (SV41) was performed, identifying regions on the PIV2 F protein that are involved in the functional interaction with the HN proteins in the induction of cell fusion. 2. The F protein of SV5 strain W3A induced cell fusion in BHK cells in the absence of the HN protein, while that of strain WR required the HN protein in the induction of cell fusion. This HN-independent fusion activity could be transferred to the WR F protein by Pro-22 in the W3A F2 subunits as represented by the mutant F protein, L22P. 3. Furthermore, by mutational and chimeric analyses using another SV5 strain T1, Glu-132 in the heptad repeat 1 domain of the F1 subunit was identified as another determinant involved in the HN-independent fusion activity. 4. The mutant L22P did not induce cell fusion in L929 cells, which enabled us to establish an L929 cell line stably expression L22P (L22P-L). Cocultivation of L22P-L with BHK cell surface. 5. An anti-L22P monoclonal antibody (mAb 21-1), which completely inhibited L22P-mediated cell fusion, was obtained. 6. The mAb 21-1 could not react with surface-localized WR F protein. In contrast the mAb 21-1 could react with L22P irrespective of its location. These observations indicate that the mAb 21-1 is a conformation-dependent antibody whose epitope may be hindered by a putative conformational change which takes place after the WR F protein is cleaved into F1 and F2. Alternatively, in the case of the L22P, this post-cleavage conformational change does not seem to occur correctly which may a prerequisite for its HN-independent fusion activity.
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