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Chapter 21 : Periplasmic Expression of Antibody Fragments
Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
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This chapter focuses on the biology and practical techniques that can help in the expression of antibody fragments in E. coli. The periplasm is often preferred for expression of soluble antibody fragments and some of the factors for this choice are discussed. The periplasm is the site of expression for only ~1/10 of the soluble proteins of E. coli and does not contain any DNA or RNA that can interfere with purification. Therefore combination of periplasmic expression with carefully considered harvest and extraction regimes can result in a very useful concentration and partial purification/enrichment of the periplasmic protein of interest. An important factor for enabling useful levels of protein expression is good selection or design of the expression plasmid. The key areas considered here are: (i) plasmid copy number/ origin of replication, (ii) constitutive versus inducible promoter, (iii) resistance/selection marker, and (iv) design of the coding region. The phoA promoter along with depletion of phosphate has also been used to good effect for the production of antibody fragments. A notional advantage of periplasmic expression over extracellular expression is the ability to concentrate the product simply by harvesting the cells by centrifugation or filtration and avoiding vortex-type protein damage. The chapter describes various designs of antibody fragments along with the engineered adaptations and improvements to both the fragment and the host. The endoplasmic reticulum of eukaryotes is the natural site for the folding and assembly of antibodies.
Key Concept Ranking
- Outer Membrane Protein A
Schematic representation of full-length IgG1 (human 71 isotype). Native IgG consists of two heavy-chain and two light-chain polypeptides. Each heavy chain has four domains: one variable (Vh) and three constant (CH1-hinge-CH2-CH3). Each light chain has two domains: one variable (VL) and one constant (CL). The two heavy chains are covalently linked by disulfide bonds between hinges and each light chain is attached to a heavy chain by a disulfide bond. In native human IgG carbohydrate is attached to each heavy chain at Asn297 of the CH2 domains.
Antibody fragments produced in E. coli a
Protein sequences of useful signal peptides
Examples of translational fusion partners for periplasmic proteins
Examples of fusion partners and cleavage regimes for periplasmic expression of antibody fragments
Comparison of periplasmic extraction methods