Functional analysis of glycosylation in Etanercept: Effects over potency and stability

Decoding Protein Glycosylation by an Integrative Mass Spectrometry-Based De Novo Sequencing Strategy

Glycoproteins, representing more than 50% of human proteins and most biopharmaceuticals, are crucial for regulating various biological processes. The complexity of multiple glycosylation sites often leads to incomplete sequence coverage and ambiguous glycan modification profiles. Here, we developed an integrative mass spectrometry-based approach for decoding unknown glycoproteins, which is featured with the combination of deglycosylation-mediated de novo sequencing with glycosylation site characterization. We utilized the enzymatic deglycosylation of N-/ O-glycans to achieve comprehensive sequence coverage. Additionally, EThcD fragmentation enables the identification of high-quality long peptides, facilitating precise protein assembly. We subsequently applied this method to de novo sequencing of the highly glycosylated therapeutic fusion protein Etanercept (Enbrel). We also sequenced three new tumor necrosis factor receptor:Fc-fusion biologics with largely unknown sequences, unveiling subtle distinctions in the primary sequences. Furthermore, we characterized N- and O-glycosylation modifications of these proteins at subunit, glycopeptide, and glycan levels. This strategy bridges the gap between the de novo sequencing and glycosylation modification, providing comprehensive information on the primary structure and glycosylation modifications for glycoproteins. Notably, our method could be a robust solution for accurate sequencing of the glycoproteins and has practical value not only in basic research but also in the biopharmaceutical industry.

In Silico and Experimental Evidence for the Stabilization of rhEPO by Glycine, Glutamic Acid and Lysine

The available literature indicates that amino acids can stabilize proteins. Our experimental data demonstrated that lysine and glutamic acid can stabilize recombinant human erythropoietin (rhEPO) at 40°C for at least 1 month, as measured by RP-UPLC. Studies with different excipient concentrations demonstrated optimal concentrations of these amino acids within 10-12 mM. The results suggest that a lower concentration of amino acids may not be sufficient to stabilize formulations, while a higher concentration of amino acids can lead lower stability. In silico studies highlighted the importance of the FA4G4S4 model in experimental glycosylation determination, particularly in glycoprotein analysis. We obtained insights into the interactions between the glycosylated ligands of rhEPO and amino acids, as well as their impact on protein behavior and stability. We observed different interactions between the amino acids glycine, glutamic acid, and lysine and the rhEPO protein using this model in docking experiments. They also made it easier to find specific interaction areas by analyzing ligand‒protein interaction fingerprints (PLIFs). This demonstrated how the ligands bind to the proteins or remain outside their vicinity. Furthermore, this study revealed specific places where ligands and rhEPO residues can interact, which helps us learn more about how they stabilize rhEPO.

Isolation, physicochemical, and structure-function relationship of the hydrophobic variant of Fc-fusion proteins that bind to TNF-α receptor, HS002 and HS002A

HS002 is the recombinant human tumor necrosis factor-α receptor Ⅱ: IgG Fc fusion protein licensed in China to treat rheumatism and psoriasis. The aim of this study was to isolate and characterize the hydrophobic freeze-dried powder injection (HS002) and ampoule injection (HS002A) variants derived from proteins of the same sequence and then to explore the structure-function relationship. Extensive physicochemical and structural testing was performed during a side-by-side comparison of the monomer peak and variant. Then the TNF-α-related binding activity, cell biological activity and affinity with FcRn were analyzed. Finally, a transformation study of the hydrophobic variant was performed under serum-like redox conditions. This research revealed that HS002A has similar physicochemical and structure-function relationship profiles to those of HS002. The hydrophobic variant exhibited the presence of new incorrect disulfide bridging. At the same time, this novel disulfide scrambled species structure-function relationship was found to be the molecular basis for reduced TNF-α binding and cell biological activities. In addition, incorrect disulfide bridging was found to be reversible under serum-like redox conditions, restoring TNF-α binding and cell biological activities to almost normal levels, all of which indicate that the variant is probably irrelevant to clinical efficacy once the drug enters the bloodstream.