Table of Contents
Molecular Biology International
Volume 2016, Article ID 4732791, 11 pages
Research Article

Soluble Expression and Characterization of Biologically Active Bacillus anthracis Protective Antigen in Escherichia coli

1Microbiology Division, Defence Research and Development Establishment, Jhansi Road, Gwalior 474002, India
2Entomology Division, Defence Research Laboratory, Tezpur, Assam 784001, India

Received 30 September 2015; Accepted 12 January 2016

Academic Editor: Surjit Kaila S. Srai

Copyright © 2016 Nagendra Suryanarayana et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Bacillus anthracis secretory protein protective antigen (PA) is primary candidate for subunit vaccine against anthrax. Attempts to obtain large quantity of PA from Escherichia coli expression system often result in the formation of insoluble inclusion bodies. Therefore, it is always better to produce recombinant proteins in a soluble form. In the present study, we have obtained biologically active recombinant PA in small scale E. coli shake culture system using three different expression constructs. The PA gene was cloned in expression vectors bearing trc, T5, and T7 promoters and transformed into their respective E. coli hosts. The growth conditions were optimized to obtain maximum expression of PA in soluble form. The expression construct PA-pET32c in DE3-pLysS E. coli host resulted in a maximum production of soluble PA (15 mg L−1) compared to other combinations. Purified PA was subjected to trypsin digestion and binding assay with lethal factor to confirm the protein’s functionality. Biological activity was confirmed by cytotoxicity assay on J774.1 cells. Balb/c mice were immunized with PA and the immunogenicity was tested by ELISA and toxin neutralization assay. This study highlights the expression of soluble and biologically active recombinant PA in larger quantity using simpler E. coli production platform.