Large-Scale Production in 'Escherichia coli' TG1 and Purification of Llama Single Domain Antibody ToxA5.1 Against 'Clostridium difficile' Toxin A

Abstract

Drug resistant strains of Clostridium difficile are a major health concern with over 3 million cases costing over 1 billion $ per year in the United-States. The diseases associated with these bacteria (CDAD) are toxin-mediated which offers a mean of treating and lessening the severity of CDAD symptoms. Toxin inactivation via antibodies therapy can drastically reduce CDAD morbidity and this project was aiming at investigating the large-scale production and recovery of a novel llama single domain antibody (pSJF2H-ToxA5.1) in recombinant Escherichia coli TG1 targeting C. difficile enterotoxin A (TcdA). In order to achieve these objectives, the project was divided into four segments: 1) ToxA5.1 being an intracellular recombinant protein, obtaining a high biomass production was the first step towards large-scale production. To achieve HCDC, effects of initial glucose concentration and pH-stat feeding strategy were studied; 2) Upon achieving HCDC, effects of parameters such as temperature, induction timing and media supplementation with complex nitrogen sources were investigated; 3) Once large-scale production of ToxA5.1 was obtained, the recombinant protein needed to be recovered and a selective cell lysis scheme where synergistic lysis effects of Triton X-100 and temperature were studied. And finally 4) Single-step purification using nickel nanoparticles (NNP) synthesized via a modified polyol method was studied. Combining the HCDC strategy with a temperature shift and yeast extract addition at the time of induction, ToxA5.1 concentration of 127 mg/L was obtained. Synergistic and selective cell lysis using Triton X-100 and temperature was achieved where 95% of the available ToxA5.1 was recovered and still functional while ToxA5.1 fraction in the resulting lysate increased to 27% in the cell lysate. Single-step purification was achieved using the synthesized NNP which proved to be highly selective and could be used up to five times. Diameter of the NNP synthesized was controlled by using various concentration of ranging from 131 ± 80 nm to 47 ± 20 nm. Using experimental data from binding isotherm, the ToxA5.1-NNP system was modeled.