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. 2021 Feb 10;9:630551. doi: 10.3389/fbioe.2021.630551

FIGURE 2.

FIGURE 2

New developments in E. coli strain’s engineering to tackle the issue of IBs formation in recombinant protein expression. Amongst the issues is its inability to catalyze di-sulfide bond formation, glycosylation, and the high strength of expression. (A) SHuffle strains enable disulfide bond formation by oxidized thioredoxins and mutant AhpC* transfers electrons to GSH/glutaredoxin pathway allowing for the reduction of oxidized ribonucleotide reductase which is essential for growth. (B) N- or O-glycosylation in glycoengineered E. coli is conducted by the protein glycosylation (pgl) locus which is responsible for the biosynthesis of the glycans. Glycoengineered strains like E. coli CLM24 could potentially be engineered to be “leaky” facilitating secretion of the glycoprotein to culture media. As proof of concept, E. coli CLM37 was engineered to be “leaky” by deleting the Braun’s lipoprotein (lpp gene) which connects the outer membrane to the peptidoglycan layer. (C) Various E. coli strains have been engineered (1, 2, 3) to modulate transcription or (4, 5) inhibition of either orthogonal T7 RNA polymerases (RNAP). There are also those strains engineered in (6) decoupling of host cell growth from recombinant protein production via inhibition of E. coli RNAPs.