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Focus: Protein Cleavage

ProTEV Protease for Fusion Protein Processing

The ProTEV Protease is an improved 50kDa version of the Nla protease from Tobacco Etch Virus (TEV), which has been engineered to be more stable than native TEV protease for prolonged enzymatic stability (1–3). It is used primarily to cleave affinity tags from fusion proteins during or after affinity purification.

By Jessica Anderson, Ph.D., Jami English, M.S., and John Shultz, Ph.D.
Promega Corporation

Published in April 2008

Introduction

Many proteins are expressed as fusion partners with affinity tags, such as glutathione-S-transferase (GST) or maltose binding protein (MBP), to selectively bind the proteins using affinity purification resins. While such resins yield high-purity protein quickly, the large affinity tags are undesirable for some downstream applications. Therefore, most expression vectors are designed with a specific protein cleavage site between the two fusion partners to remove the affinity tag after purification.

A common protease used to remove affinity tags, Factor Xa (FXa; Cat.# V5581), may also cleave the fusion protein because its four-amino acid recognition sequence is quite common. In contrast, ProTEV Protease (Cat.# V6051) recognizes a rare amino acid sequence, EXXYXQ, where X is any amino acid and cleavage occurs after the glutamine residue (4,5). In addition, cleavage sites for TEV protease are found in many common vectors including the the pFN2A and pFN2K (GST) Flexi® Vectors (Cat.# C8461 and C8471).

Specificity of ProTEV Protease

ProTEV Protease is manufactured to a high standard of purity and is free from nonspecific activity. Overdigestion of a protein panel with ProTEV Protease results in cleavage of only the control protein containing a ProTEV Protease recognition sequence (Figure 1). Since the ProTEV Protease recognition sequence is uncommon, unintentional cleavage of the protein of interest is rare.

thumbnail-ProTEV Protease has highly specific proteolytic activity.
ProTEV Protease has highly specific proteolytic activity.

Figure 1. ProTEV Protease has highly specific proteolytic activity. Fifteen micrograms of six different proteins were incubated with or without 10 units of ProTEV Protease for 72 hours at 30°C. Digestion of the proteins was analyzed by SDS-PAGE and stained with SimplyBlue™ SafeStain (Invitrogen). Lane M, SeeBlue® Plus2 (Invitrogen); lane 1, ProTEV Protease alone; lanes 2,3, GST-MBP with TEV protease site; lanes 4,5, GST-HaloTag® fusion protein with FXa protease site; lanes 6,7, bovine serum albumin (BSA); lanes 8,9, phosphorylase B (Sigma); lanes 10,11, β-galactosidase (Sigma); lanes 12,13, QuantiLum® Recombinant Luciferase.

Cleavage Conditions for ProTEV Protease

ProTEV Protease is provided with a reaction buffer at pH 7; however, the protease is active over a pH range of 5.5–8.5, allowing it to be used under the conditions most appropriate for the protein of interest. The greatest activity of ProTEV Protease occurs at 30°C, but the protease will cleave fusion proteins over a temperature range of 4–34°C. As with many enzymes, ProTEV Protease cleaves more slowly as the temperature is decreased (Table 1).

Table 1. Time Course of ProTEV Protease Cleavage of GST-MBP at Various Temperatures. Reactions were set up with 20µg of GST-MBP fusion protein and 1 unit of ProTEV Protease. The reactions were incubated at the indicated temperatures, and aliquots were removed at the indicated times. Samples were analyzed by SDS-PAGE and quantified by densitometry.
% Cleavage
Time (minutes) 4°C 16°C 22°C 30°C
30 32 63 63 76
60 41 77 82 93
120 56 90 92 97
180 64 98 97 98

For more details on ProTEV Protease, read the full-length Promega Notes article.

References

  1. Dougherty, W.G. and Parks, T.D. (1991) Post-translational processing of the tobacco etch virus 49-kDa small nuclear inclusion polyprotein: identification of an internal cleavage site and delimitation of VPg and proteinase domains. Virology 183, 449–56.
  2. Carrington, J.C. et al. (1993) Internal cleavage and trans-proteolytic activities of the VPg-proteinase (NIa) of tobacco etch potyvirus in vivo. J. Virol. 67, 6995–7000.
  3. Kapust, R.B. et al. (2001) Tobacco etch virus protease: mechanism of autolysis and rational design of stable mutants with wild-type catalytic proficiency. Protein Eng. 14, 993–1000.
  4. Dougherty, W.G. et al. (1989) Characterization of the catalytic residues of the tobacco etch virus 49-kDa proteinase. Virology 172, 302–10.
  5. Carrington, J.C. and Dougherty, W.G. (1988) A viral cleavage site cassette: identification of amino acid sequences required for tobacco etch virus polyprotein processing. Proc. Natl. Acad. Sci. USA 85, 3391–5.