Screening of soluble hemagglutinin recombinant proteins for influenza virus B/Victoria

Objective To screen the soluble hemagglutinin (HA) recombinant protein derived from B/Victoria lineages of influenza virus that possess hemagglutination activity. Methods Based on the B/Darwin/7/2019 (B/Victoria) strain, HA mutant genes BV-T1, BV-T2, and BV-T3 were obtained by fusing the leucine zipper GCN4pII and GCN4pLL trimerization motifs(T1 and T2), and bacteriophage T4 Foldon trimerization motifs(T3) to the C-terminus of the HA ectodomain. HA ectodomain mutant gene BV-ecto was also constructed as a control. These genes were inserted into pFastBac1 vector. The proteins were expressed using baculovirus-Sf9 insect cell expression system and culture supernatants of infected cells were harvested. Recombinant proteins were purified by Strep-Tactin affinity chromatography and subsequently characterized for their oligomerization degree and hemagglutination activity. Results All four mutant proteins were solubly expressed in the culture supernatant. BV-T2 and BV-T3 exhibited a high trimerization form, while BV-T1 formed predominantly trimers with minor low-order oligomers. BV-ecto existed as a monomer.BV-T1 and BV-T2 exhibited hemagglutination activity, in contrast, BV-T3 and BV-ecto lacked hemagglutination activity. Conclusions The soluble BV-T2 mutant protein present efficient trimer- ization and possesses hemagglutination activity.The leucine zipper trimerization motif GCN4pLL is suitable for the soluble expression of B/Victoria lineage HA recombinant protein and thus provides a reference for the development of soluble recombinant protein vaccines against B/Victoria virus.