• Optimized procedure to generate heavy isotope and selenomethionine-labeled proteins for structure determination using Escherichia coli-based expression systems.

      Li, Zhaopeng; Nimtz, Manfred; Rinas, Ursula; Helmholtz Centre for Infection Research (SB), Braunschweig, Germany. (2011-11)
      Generating sufficient quantities of labeled proteins represents a bottleneck in protein structure determination. A simple protocol for producing heavy isotope as well as selenomethionine (Se-Met)-labeled proteins was developed using T7-based Escherichia coli expression systems. The protocol is applicable for generation of single-, double-, and triple-labeled proteins ((15)N, (13)C, and (2)H) in shaker flask cultures. Label incorporation into the target protein reached 99% and 97% for (15)N and (13)C, respectively, and 75% of (non-exchangeable) hydrogen for (2)H labeling. The expression yields and final cell densities (OD600 ~16) were the same as for the production of non-labeled protein. This protocol is also applicable for Se-Met labeling, leading to Se-Met incorporation into the target protein of 70% or 90% using prototrophic or methionine auxotrophic E. coli strains, respectively.
    • Simple defined autoinduction medium for high-level recombinant protein production using T7-based Escherichia coli expression systems.

      Li, Zhaopeng; Kessler, Wolfgang; van den Heuvel, Joop; Rinas, Ursula; Helmholtz Centre for Infection Research (SB), Braunschweig, Germany. (2011-08)
      Protein production under the control of lac operon regulatory elements using autoinduction is based on diauxic growth of Escherichia coli on lactose after consumption of more preferred carbon substrates. A novel simple and cost-effective defined autoinduction medium using a mixture of glucose, glycerol, and lactose as carbon substrate and NH(4)(+) as sole nitrogen source without any supplementation of amino acids and vitamins was developed for T7-based E. coli expression systems. This medium was successfully employed in 96-well microtiter plates, test tubes, shake flasks, and 15-L bioreactor cultivations for production of different types of proteins achieving an average yield of 500 mg L(-1) product. Cell-specific protein concentrations and solubility were similar as during conventional isopropyl β-D-1-thiogalactopyranoside induction using Luria-Bertani broth. However, the final yield of target proteins was about four times higher, as a higher final biomass was achieved using this novel defined autoinduction broth.