Neutralizing epitope on penetration protein of vaccinia virus.

The monoclonal antibody 2D5 neutralized vaccinia virus by preventing penetration of the virus and reacting with VP23-29K. The conformation of the VP23-29K was maintained by a disulfide bond(s), and the 2D5mAb reacted stronger with the nonreduced 23-kDa form than with the reduced 29-kDa form. We selected several escape mutants. Sequences of the A17L genes, which were thought to encode the VP23-29K, did not show cognate mutation. Genomic DNA of a 2D5mAb-resistant mutant (M4) was cleaved with HindIII, and all the fragments were introduced into parental IHD-J strain vaccinia virus by transfection. Only the L fragment produced a 2D5mAb-resistant virus. Dissection of the L fragment and subsequent transfection revealed that the L1R gene induced the 2D5mAb-resistant virus. The 2D5mAb-resistant mutants showed a consensus G to A conversion at nucleotide 101 of their LIRs which would replace asparatic acid 35 with asparagine. Ishibashi-111 strain mousepox virus spontaneously resistant to 2D5mAb also had the same sequence at this region. Moreover, the VP23-29K was myristoylated as predicted by the L1R gene. The coding gene of the VP23-29K was L1R.