Whether antibody responses elicited by the N-terminus of EV71 VP4 are capable of neutralizing CA16 virions still remains to be investigated. Conclusions In summary, this study identified an immunodominant epitope located at the N-terminal of EV71 VP4 protein. The fusion proteins of HBcAg and N-terminal of EV71 VP4-derived

peptide were able to spontaneously assemble into chimeric VLPs. Mice immunization with these chimeric VLPs elicited neutralizing antibodies against EV71 of different genotypes. The “core sequence” responsible for immune stimulation was found to be highly conserved across different EV71 genotypes. Methods Plasmid constructions and bacterial strains The peptide (VP4N20) that corresponds to first 20 residues at the N-terminal of VP4 of EV71 (Bj08) was inserted to HBcAg (HBc-N149) loop region between amino acids 78 and 79. The fusion protein was named as HBc-N149-VP4N20. selleck screening library To construct the plasmid expressing the fusion protein, DNA fragment encoding HBc-N149-VP4N20 was synthesized and amplified using primers P1u (5′- CCGCTCGAGCACCACGGTGGTT-3′)

and P1d (5′- GGAATTCCATATGGATATTGATCCGTATAAAG-3′). The PCR products were double-digested by XhoI and NdeI and subsequently inserted into the vector pET22b(+) (Novagen, USA). DNA fragment encoding HBc-N149 was amplified by using the primers P1u, P2d (5′-TGGGCAGCAATCTGGAAGATCCGGCGAGCCGCGAACTG-3′), P2u (5′- ACCAGTTCGCGGCTCGCCGGATCTTCCAGATTGCTGCCCA-3′) and P1d by using HBc-N149-VP4N20-encoding gene as a template and further inserted into the vector pET22b (+). The accuracy of the constructs was confirmed by sequencing. https://www.selleckchem.com/products/kpt-330.html E. coli strain BL21 (DE3) (BeiJing TIANGEN BIOTECH, China) were used for protein expression. Expression and purification of recombinant DNA ligase proteins Overnight cultures of BL21 (DE3) cells harboring the recombinant plasmids were diluted 1:400 in 1 L of LB broth containing 100 μg/ml ampicillin, and grown until reaching an OD600 of 0.4-0.6. Protein expression was then induced by 0.1 mM of isopropyl-β-d-thiogalactopyranoside (IPTG). After shaking at 37°C for

5 h, the bacteria were collected by centrifugation at 12,000 rpm for 10 min at 4°C, and the pellets were resuspended in 100 ml of balance buffer (pH 8.0, 50 mM Tris, 100 mM NaCl, 10 mM imidazole). For protein purification, the bacterial cells were lysed by ultrasonication, followed by centrifugation at 13,000 rpm for 15 min at 4°C to remove bacterial debris. The clear supernatant was applied to a Ni Sepharose column (GE Healthcare Life Sciences, USA) according to the manufacturer’s recommendations. The columns were washed with washing buffer (pH 8.0, 50 mM Tris–HCl, 100 mM NaCl, 50 mM imidazole,) and bound proteins were eluted with elution buffer (pH 8.0, 50 mM Tris–HCl, 100 mM NaCl, 200 mM imidazole). The peak fractions were collected and analyzed by SDS-PAGE. The purity of the samples was determined by densitometric scanning. The proteins were dialyzed to PBS buffer (pH7.