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Genetic incorporation of unnatural amino acids into proteins in Mycobacterium tuberculosis.

ABSTRACT: New tools are needed to study the intracellular pathogen Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), to facilitate new drug discovery and vaccine development. We have developed methodology to genetically incorporate unnatural amino acids into proteins in Mycobacterium smegmatis, BCG and Mtb, grown both extracellularly in culture and inside host cells. Orthogonal mutant tRNATyr/tyrosyl-tRNA synthetase pairs derived from Methanococcus jannaschii and evolved in Escherichia coli incorporate a variety of unnatural amino acids (including photocrosslinking, chemically reactive, heavy atom containing, and immunogenic amino acids) into proteins in response to the amber nonsense codon. By taking advantage of the fidelity and suppression efficiency of the MjtRNA/pIpaRS pair in mycobacteria, we are also able to use p-iodophenylalanine to induce the expression of proteins in mycobacteria both extracellularly in culture and inside of mammalian host cells. This provides a new approach to regulate the expression of reporter genes or mycobacteria endogenous genes of interest. The establishment of the unnatural amino acid expression system in Mtb, an intracellular pathogen, should facilitate studies of TB biology and vaccine development.

SUBMITTER: Wang F

PROVIDER: S-EPMC2825273 | biostudies-literature | 2010 Feb

REPOSITORIES: biostudies-literature

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Genetic incorporation of unnatural amino acids into proteins in Mycobacterium tuberculosis.

Wang Feng F Robbins Scott S Guo Jiantao J Shen Weijun W Schultz Peter G PG

PloS one 20100222 2

New tools are needed to study the intracellular pathogen Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), to facilitate new drug discovery and vaccine development. We have developed methodology to genetically incorporate unnatural amino acids into proteins in Mycobacterium smegmatis, BCG and Mtb, grown both extracellularly in culture and inside host cells. Orthogonal mutant tRNATyr/tyrosyl-tRNA synthetase pairs derived from Methanococcus jannaschii and evolved in Esche ...[more]

PMID: 20179771

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Project description:Site-directed spin labeling (SDSL) is a powerful tool for the characterization of protein structure and dynamics; however, its application in many systems is hampered by the reliance on unique and benign cysteine substitutions for the site-specific attachment of the spin label. An elegant solution to this problem involves the use of genetically encoded unnatural amino acids (UAAs) containing reactive functional groups that are chemically orthogonal to those of the 20 amino acids found naturally in proteins. These unique functional groups can then be selectively reacted with an appropriately functionalized spin probe. In this chapter, we detail the genetic incorporation of the ketone-bearing amino acid p-acetyl phenylalanine (pAcPhe) into recombinant proteins expressed in E. coli. Incorporation of pAcPhe is followed by chemoselective reaction of the ketone side chain with a hydroxylamine-functionalized nitroxide to afford the spin-labeled side chain "K1," and we present two protocols for successful K1 labeling of proteins bearing site-specific pAcPhe. We outline the basic requirements for pAcPhe incorporation and labeling, with an emphasis on practical aspects that must be considered by the researcher if high yields of UAA incorporation and efficient labeling reactions are to be achieved. To this end, we highlight recent advances that have led to increased yields of pAcPhe incorporation, and discuss the use of aniline-based catalysts allowing for facile conjugation of the hydroxylamine spin label under mild reaction conditions. To illustrate the utility of K1 labeling in proteins where traditional cysteine-based SDSL methods are problematic, we site-specifically K1 label the cellular prion protein at two positions in the C-terminal domain and determine the interspin distance using double electron-electron resonance EPR. Recent advances in UAA incorporation and ketone-based bioconjugation, in combination with the commercial availability of all requisite reagents, should make K1 labeling an increasingly viable alternative to cysteine-based methods for SDSL in proteins.

Dataset Information

Genetic incorporation of unnatural amino acids into proteins in Mycobacterium tuberculosis.

Publications

Genetic incorporation of unnatural amino acids into proteins in Mycobacterium tuberculosis.

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