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Genetic incorporation of a metal-ion chelating amino acid into proteins as a biophysical probe.

ABSTRACT: A metal-ion chelating amino acid, (8-hydroxyquinolin-3-yl)alanine, was genetically encoded in E. coli by an amber nonsense codon and corresponding orthogonal tRNA/aminoacyl-tRNA synthetase pair. The amino acid was incorporated into TM0665 protein, and the mutant protein was cocrystallized with Zn(2+) to determine the structure by SAD phasing. The structure showed a high occupancy of the heavy metal bound to the HQ-Ala residue, and the heavy metal provided excellent phasing power to determine the structure. This method also facilitates the de novo design of metalloproteins with novel structures and functions, including fluorescent sensors.

SUBMITTER: Lee HS

PROVIDER: S-EPMC2679636 | biostudies-literature | 2009 Feb

REPOSITORIES: biostudies-literature

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Genetic incorporation of a metal-ion chelating amino acid into proteins as a biophysical probe.

Lee Hyun Soo HS Spraggon Glen G Schultz Peter G PG Wang Feng F

Journal of the American Chemical Society 20090201 7

A metal-ion chelating amino acid, (8-hydroxyquinolin-3-yl)alanine, was genetically encoded in E. coli by an amber nonsense codon and corresponding orthogonal tRNA/aminoacyl-tRNA synthetase pair. The amino acid was incorporated into TM0665 protein, and the mutant protein was cocrystallized with Zn(2+) to determine the structure by SAD phasing. The structure showed a high occupancy of the heavy metal bound to the HQ-Ala residue, and the heavy metal provided excellent phasing power to determine the ...[more]

PMID: 19193005

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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 a metal-ion chelating amino acid into proteins as a biophysical probe.

Publications

Genetic incorporation of a metal-ion chelating amino acid into proteins as a biophysical probe.

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