Comprehensive Analysis of Tryptic Peptides Arising from Disulfide Linkages in NISTmAb and Their Use for Developing a Mass Spectral Library

A simplified non-reduced peptide mapping method with faster and efficient enzymatic digestion for characterization of native disulfide bonds in monoclonal and bispecific antibodies

Development of monoclonal and bispecific antibody-based protein therapeutics requires detailed characterization of native disulfide linkages, which is commonly achieved through peptide mapping under non-reducing conditions followed by liquid chromatography-mass spectrometry (LC-MS) analysis. One major challenge of this method is incomplete protein digestion due to insufficient denaturation of antibodies under non-reducing conditions. For a long time, researchers have explored various strategies with the aim of efficiently digesting antibody drugs when the disulfide bonds remain intact, but few could achieve this by using a simple and generic approach with well controlled disulfide scrambling artifacts. Here, we report a simple method for fast and efficient mapping of native disulfides of monoclonal and bispecific antibody-based protein therapeutics. The method was optimized to achieve optimal digestion efficiency by denaturing proteins with 8 M urea plus 0-1.25 M guanidine-HCl at elevated temperature (50 °C), followed by two-step digestion with trypsin/Lys-C mix using a one-pot reaction. The only parameter that needs to be optimized for different proteins is the concentration of guanidine-HCl present. This simplified sample preparation eliminated buffer exchange and can be completed within three hours. By using this new method, all native disulfide bonds were confirmed for these monoclonal and bispecific antibodies with high confidence. When compared with a commercial kit utilizing low-pH digestion condition, the new method demonstrated higher digestion efficiency and shorter sample preparation time. These results suggest this new one-pot-two-step digestion method is suitable for the characterization of antibody disulfide bonds, particularly for those antibodies with digestion-resistant domains under typical digestion conditions.

Effect and mechanism of C-terminal cysteine on the properties of HEV p222 protein

Preliminary investigations have demonstrated that the cysteines located at the C-terminus of HEV ORF2 protein exhibits disulfide bonding capability during virus-like particles (VLPs) assembly. However, the effect and mechanism underlying the pairing of disulfide bonds formed by C627, C630, and C638 remains unclear. The p222 protein encompasses C-terminus and serves as a representative of HEV ORF2 to investigate the specific impacts of C627, C630, and C638. The three cysteines were subjected to site-directed mutagenesis and expressed in prokaryotes; Both the mutated proteins and p222 underwent polymerization except for p222A; Surprisingly, only p222 was observed as abundant spherical particles under transmission electron microscope (TEM); Stability and immunogenicity of the p222 exhibited higher than other mutated proteins; LC/MS/MS analysis identified four disulfide bonds in the p222. The novel findings suggest that the three cysteines contribute to structural and functional properties of ORF2 protein, highlighting the indispensability of each cysteine.

Mass Spectrometric De Novo Sequencing of Natural Peptides

Natural peptides secreted under stress conditions by many organisms are bioactive molecules with a broad spectrum of activities. These molecules could become potential models for novel pharmaceuticals, to which bacteria, according to modern scientific concepts, do not have and cannot develop resistance. Taking this into consideration, it is necessary to clarify the amino acid sequences of such peptides. Here we describe our approach to de novo sequencing of amphibians' skin secretion peptides.