Expression of pB602L polypeptide fragments
To map the epitope recognized by each of the mAbs, a progressive procedure was adopted to screen the mAbs by Western blot assay against overlapped polypeptides from the longest to the shortest. A total of 18 polypeptides were designed and screened, and their lengths and locations in pB602L are showed in Fig. 1A, B. Polypeptides S1-9 were expressed inE. coli BL21 (DE3) and their encoding gene fragments were amplified using the primers presented in Table 1. The plasmid pGEX-6P-B602L, which encoded the full-length pB602L protein, was used as a template to amplify these genes. The gene fragments encoding the polypeptides S10-18 were synthesized and cloned into pGEX-6p-1 vector by Genscript Biotech Corporation (Nanjing, Jiangsu, China). The production procedure of these polypeptides was the same with that of the above mentioned for producing the full-length pB602L.