Characterization of the internal translation initiation region in monoclonal antibodies expressed in Escherichia coli
Erik M. Leith, William B. O'Dell, Na Ke, Colleen McClung, Mehmet Berkmen, Christina Bergonzo, Robert G. Brinson, Zvi Kelman
Monoclonal antibodies (mAbs) represent an important platform for the development of biotherapeutic products. While most mAbs are produced in mammalian cells, there are several examples of mAbs made in Escherichia coli, including therapeutic fragments. When the NISTmAb and adalumimab (Humira) were expressed in E. coli, a truncation of the heavy chain was observed. N-terminal sequencing and mutagenesis analysis indicated that the truncation is a result of internal translation initiation from a GTG codon. Using computational and biochemical approaches it was demonstrated that translation initiates from a weak Shine-Dalgarno sequence, and is facilitated by a putative ribosomal protein S1 binding site. This internal initiation region is likely an unintended result of codon optimization for E. coli expression, and the amino acid motif from which it is derived was identified. The implications for E. coli mAbs expression and codon optimization are discussed.