Molecular mechanism responsible for the hyperexpression of baculovirus polyhedrin

One of the amazing phenomena in the baculovirus life cycle is the hyperexpression of the very late gene, polyhedrin (polh), causing the production of the occlusion bodies where progeny virions are embedded. However, to date, the molecular mechanism underlying its hyperexpression is not completely elucidated. Considering that, in this review, the mechanism responsible for its hyperexpression from the previous studies up to now was comprehensively summarized from three aspects, namely, the structure characteristics of the polh promoter and transcription regulation, the structure and translation regulation of the polh mRNA, and especially the regulators that influence the expression of polh gene. Moreover, this review will help us obtain a better understanding about the hyperexpression of polh, and also provide guidance for improving the expression efficiency of the foreign proteins by adopting the baculovirus expression vector system.

Development of biparatopic bispecific antibody possessing tetravalent scFv-Fc capable of binding to ROBO1 expressed in hepatocellular carcinoma cells

There is no standard structural format of the biparatopic bispecific antibody (bbsAb) which is used against the target molecule because of the diversity of biophysical features of bispecific antibodies (bsAbs). It is therefore essential that the interaction between the antibody and antigen is quantitatively analyzed to design antibodies that possess the desired properties. Here, we generated bsAbs, namely, a tandem scFv-Fc, a diabody-Fc, and an immunofusion-scFv-Fc-scFv, that possessed four scFv arms at different positions and were capable of recognizing the extracellular domains of ROBO1. We examined the interactions between these bsAbs and ROBO1 at the biophysical and cellular levels. Of these, immunofusion-B2212A scFv-Fc-B5209B scFv was stably expressed with the highest relative yield. The kinetic and thermodynamic features of the interactions of each bsAb with soluble ROBO1 (sROBO1) were validated using surface plasmon resonance and isothermal titration calorimetry. In all bsAbs, the immunofusion-scFv-Fc-scFv format showed homogeneous interaction with the antigen with higher affinity compared with that of monospecific antibodies. In conclusion, our study presents constructive information to design druggable bbsAbs in drug applications.

Structural insight and stability of TNFR-Fc fusion protein (Etanercept) produced by using transgenic silkworms

Therapeutic proteins expressed using transgenic animals have been of great interest for several years. Especially, transgenic silkworm has been studied intensively because of its ease in handling, low-cost, high-yield and unique glycosylation patterns. However, the physicochemical property of the therapeutic protein expressed in transgenic silkworm remains elusive. Here, we constructed an expression system for the TNFR-Fc fusion protein (Etanercept) using transgenic silkworm. The TNFR-Fc fusion protein was employed to N-glycan analysis, which revealed an increased amount of afucosylated protein. Evidence from surface plasmon resonance analysis showed that the TNFR-Fc fusion protein exhibit increased binding affinity for Fcγ receptor IIIa and FcRn compared to the commercial Etanercept, emphasizing the profit of expression system using transgenic silkworm. We have further discussed the comparison of higher order structure, thermal stability and aggregation of the TNFR-Fc fusion protein.

Highly sensitive HPLC analysis and biophysical characterization of N-glycans of IgG-Fc domain in comparison between CHO and 293 cells using FcγRIIIa ligand

Quality control of monoclonal antibodies is challenging due in part to the diversity of post‐translational modifications present. The regulation of the N‐glycans of IgG‐Fc domain is one of the key factors to maintain the safety and efficacy of antibody drugs. The FcγRIIIa affinity column is an attractive tool for the precise analysis of the N‐glycans in IgG‐Fc domain. We used the mutant FcγRIIIa, which is produced in Escherichia coli and is therefore not glycosylated, as an affinity reagent to analyze the N‐glycans of monoclonal antibodies expressed in Expi293 and ExpiCHO cells. The monoclonal antibodies expressed in these cells showed very different chromatograms, because of differences in terminal galactose residues on the IgG‐Fc domains. We also carried out kinetic and thermodynamic analyses to understand the interaction between monoclonal antibodies and the mutant FcγRIIIa. Expi293 cell‐derived monoclonal antibodies had higher affinity for the mutant FcγRIIIa than those derived from ExpiCHO cells, due to slower off rates and lower binding entropy loss. Collectively, our results suggest that the FcγRIIIa column can be used to analyze the glycosylation of antibodies rapidly and specifically.