Single Amino Acid Substitution in LC-CDR1 Induces Russell Body Phenotype that Attenuates Cellular Protein Synthesis Through eIF2α Phosphorylation and Thereby Downregulates IgG Secretion Despite Operational Secretory Pathway Traffic

Hasegawa H, et al., doi: 10.1080/19420862.2017.1314875, Mabs, 2017

Differences in Amino acid sequence in the variable region of immunoglobulin (Ig) can have dramatic effects on stability, efficiency of biosynthesis (due to differences in secretion outputs), and on the antigen-binding characteristics. Described herein is a study directed towards the investigation of underlying mechanisms of secretion-level variance between two distinct human IgG2k monoclonal antibodies (mAbs). The two mAbs differ only by one amino acid residue in the light chain complementarity-determining region 1 (LC-CDR1). Human IgG in the harvested cell culture media were quantified by Bio-Layer Interferometry (BLI). A Pall ForteBio Octet RED96 system equipped with Protein A (ProA) biosensor probes was used to perform BLI experiments. Although the primary sequences of the parental mAb and the variant mAb are nearly identical, variant mAb induced the aggregation of enlarged globular structures called Russell bodies (RBs), leading to 20-fold less IgG secretion. Overall findings of this study demonstrate that a single amino acid substitution in the LC-CDR1 is sufficient to change the efficiency of IgG secretion.

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