High-level secretory expression, purification, and characterization of an anti-human Her II monoclonal antibody, trastuzumab, in the methylotrophic yeast <i>Pichia pastoris</i>

Abstract

DNA fragments encoding the light chain and heavy chain genes of an anti-human HER II antibody, trastuzumab, fused with an egg-lysozyme signal peptide were synthesized based on the codon bias of the methylotrophic yeast Pichia pastoris . These fragments were inserted into a site between the AOX 1-promoter and -terminator in pPICZ A to be expressed by P. pastoris . The expression vector was linearized, and introduced into P. pastoris GS115 by electroporation. After the checking of several transformants with PCR to ensure a precise insertion, one was selected and cultured to examine antibody production. The level of production reached 10 mg/L in a flask with medium containing 1% methanol. The heavy chain and light chain of the product were assembled to form a hetero tetramer, as detected by dodecyl sulfate polyacryla mide gel electrophoresis (SDS-PAGE). N-terminal ami no acid sequencing revealed that the signal peptides of both chains were well processed. The mobility of the product in SDS-PAGE after treatment with Peptide N-Glycosidase F indicated the heavy chain to be N-glycosylated. Further analysis of the N-glycans with a mass spectrometer revealed a mixture of Man 9 -GlcNAc 2 , Man 10 -GlcNAc 2, Man 11 -GlcNAc 2 and Man 12 - GlcNAc 2 , but no hyper-mannosylated glycans. ELISA, surface plasmon resonance, and flow cytometric studies showed the affinity curve and K d value for the antigen, HER II, and reactivity to a HER2-overexpressing breast cancer cell-line, SK-BR-3, to be almost the same as for the clinically used trastuzumab produced by CHO.