| Abstrakt: |
The nontoxic B subunit ofEscherichia coliheat-labile enterotoxin (EtxB) is a convenient carrier molecule for the attachment and delivery of heterologous peptides into eukaryotic cells. To evaluate the properties of such EtxB-based fusion proteins an efficient method for their production and purification is required. High-level production and purification of native EtxB has been achieved using heterologous expression and secretion in a marineVibrio(Amin, T., and Hirst, T.R., 1994,Protein Expression Purif.5, 198–204). However, the use of this method to isolate EtxB fusion proteins has been precluded because of their susceptibility to degradation by extracellular proteases secreted by members of theVibrionaceae.In this paper a method is described for production of EtxB–pol, comprising the enterotoxin B subunit linked to a 27-residue C-terminal fragment of Pol, the catalytic subunit of DNA polymerase of herpes simplex virus type 1 (HSV-1). Following assessment of the relative efficacy of differentVibriostrains as hosts for EtxB–pol expression, the chimera was produced at the highest level of 3.5 mg/liter by cultures ofVibriosp.60. Addition of 0.3 mMEDTA to the growth medium blocked proteolysis of the secreted EtxB–pol fusion protein, which was then purified to homogeneity using ammonium sulfate fractionation and hydrophobic interaction chromatography, with a yield of 57%. Purified EtxB–pol reacted with both anti-EtxB and anti-Pol peptide antibodies, and was able to specifically bind UL42, a processivity factor which normally binds to the C-terminal region of HSV-1 Pol. This modified method for expression and purification of EtxB–pol should be of general utility for the preparation of other EtxB-based fusion proteins. |
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