title: Cell-free protein production for NMR studies.
abstract: The cell-free expression system using an Escherichia coli extract is a practical method for producing isotope-labeled proteins. The advantage of the cell-free system over cellular expression is that any isotope-labeled amino acid can be incorporated into the target protein with minimal scrambling, thus providing opportunities for advanced isotope labeling of proteins. We have modified the standard protocol for E. coli cell-free expression to cope with two problems specific to NMR sample preparation. First, endogenous amino acids present in the E. coli S30 extract lead to dilution of the added isotope. To minimize the content of the remaining amino acids, a gel filtration step is included in the preparation of the E. coli extract. Second, proteins produced by the cell-free system are not necessarily homogeneous due to incomplete processing of the N-terminal formyl-methionine residue, which complicates NMR spectra. Therefore, the protein of interest is engineered to contain a cleavable N-terminal histidine-tag, which generates a homogeneous protein after the digestion of the tag. Here, we describe the protocol for modified E. coli cell-free expression.
authors.affiliation: Graduate School of Science, Nagoya University, Nagoya, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Takeda
authors.forename: Masatsune
authors.initials: M
authors.lastname: Kainosho
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D002457:Cell Extracts; D002474:Cell-Free System / Q000378:metabolism*; D002850:Chromatography, Gel / Q000379:methods; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004926:Escherichia coli; D007553:Isotope Labeling / Q000379:methods*; D009587:Nitrogen Isotopes / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D015202:Protein Engineering / Q000379:methods; D011994:Recombinant Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002457:Cell Extracts; D009587:Nitrogen Isotopes; D011994:Recombinant Proteins; D014764:Viral Proteins; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases