Site-specific insertion of spin-labeled L-amino acids in Xenopus oocytes

Aaron M. Shafer, Tamás Kálai, Sarah Qiao Bin Liu, Kálmán Hideg, John C Voss

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

Site-specific insertion of modified amino acids in proteins expressed in living cells is an emerging field holding great promise for elucidating protein structure-function relationships, expression levels, localization, and activation states in a complex milieu. To evaluate the efficiency of amino acids modified to carry either a nitroxide spin probe or a fluorescence probe, we have developed a screen using the levels of functional luciferase protein expressed in Xenopus oocytes. Natural and modified amino acids were targeted to position 14 in firefly luciferase using an amber mutation or introducing the four-codon nucleotide GGGU. Using the amber stop codon, the incorporation efficiencies of injected tRNA charged with the native phenylalanine residue, a fluorescent NBD-alanine, or nitroxide-labeled cysteine and tyrosine amino acids ranged from 1% to 18%. While the NBD-amino acid derivative gave higher incorporation levels, the EPR signals from the spin-labeled amino acids allow for the direct assessment of aminoacylation extent and stability. Applying the four-base codon for the first time in Xenopus oocytes, we found the incorporation efficiencies were significantly lowered compared to results using the three-base amber codon. The studies presented here provide quantitative assessment of protein expression levels when using nonsense suppression to site-specifically label proteins with spectroscopic probes in oocytes. Finally, the effect of a 77-base RNA aptamer known to inhibit the eucaryotic release factor of protein synthesis was tested for its influence on nonsense incorporation in Xenopus oocytes. The combination of A34 and charged suppressor tRNA produced a 3-fold increase in the expressed TAG14-luciferase level, compared to the use of charged suppressor tRNA alone.

Original languageEnglish (US)
Pages (from-to)8470-8482
Number of pages13
JournalBiochemistry
Volume43
Issue number26
DOIs
StatePublished - Jul 6 2004

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Xenopus
Oocytes
Amino Acids
Transfer RNA
Proteins
Terminator Codon
Luciferases
Codon
Nucleotide Aptamers
Amber
Aminoacylation
Firefly Luciferases
Phenylalanine
Alanine
Cysteine
Paramagnetic resonance
Tyrosine
Labels
Nucleotides
Fluorescence

ASJC Scopus subject areas

  • Biochemistry

Cite this

Site-specific insertion of spin-labeled L-amino acids in Xenopus oocytes. / Shafer, Aaron M.; Kálai, Tamás; Liu, Sarah Qiao Bin; Hideg, Kálmán; Voss, John C.

In: Biochemistry, Vol. 43, No. 26, 06.07.2004, p. 8470-8482.

Research output: Contribution to journalArticle

Shafer, AM, Kálai, T, Liu, SQB, Hideg, K & Voss, JC 2004, 'Site-specific insertion of spin-labeled L-amino acids in Xenopus oocytes', Biochemistry, vol. 43, no. 26, pp. 8470-8482. https://doi.org/10.1021/bi035542i
Shafer, Aaron M. ; Kálai, Tamás ; Liu, Sarah Qiao Bin ; Hideg, Kálmán ; Voss, John C. / Site-specific insertion of spin-labeled L-amino acids in Xenopus oocytes. In: Biochemistry. 2004 ; Vol. 43, No. 26. pp. 8470-8482.
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