Download Maintaining the Canonical Amino Acid Alphabet

25th Croatian meeting of chemists and chemical engineers, Poreč, 2017.
Maintaining the Canonical Amino Acid Alphabet: a Story about AminoacyltRNA Synthetases
Očuvanje kanonske aminokiselinske abecede: priča o aminoacil-tRNAsintetazama
Ita Gruić Sovulj
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Department of Chemistry Faculty of Science University of Zagreb, Horvatovac 102a, 10000 Zagreb,
Croatia
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E-mail: [email protected]
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Natural evolution has selected a set of 20 canonical genetically encoded amino acids to build
a plethora of proteins that provide the biochemical foundations for life. To participate in
protein synthesis amino acids require attachment to transfer RNA molecules (tRNAs). This
reaction is accomplished by aminoacyl-tRNA synthetases (AARSs), enzymes that use ATP to
activate the matching amino acid and transfer it to the cognate tRNA, which, in turn, harbors
the corresponding anticodon triplet of the amino acid code. Some AARSs are not able to
discriminate against highly similar near-cognate amino acids in the synthetic reaction alone,
and so have evolved hydrolytic editing to clear mistakenly activated or aminoacylated amino
acids.
Preventing the incorporation of protein-building amino acids at the wrong positions is
not the only task of AARS quality control. Recent findings have indicated that editing may also
operate to block the infiltration of natural amino acids that are not coded for protein
synthesis. Using genetic, biochemical and mass spectrometry approaches we demonstrated
that in the case of leucyl-tRNA synthetase the main physiological role of editing is to preclude
toxic misincorporation of the non-canonical amino acid norvaline at protein positions coded
for leucine [1,2]. Norvaline accumulates under oxygen limiting conditions arguing for a critical
role for editing in cellular adaptation to the various conditions of growth.
Given the lack of evolutionary pressure against unnatural compounds, it had been
assumed that editing would not be an obstacle for the use of artificial amino acids as protein
building blocks. Yet, we have recently demonstrated that participation of trifluorethylglycine
in protein translation takes place only after silencing of weak editing by isoleucyl-tRNA
synthetase [3]. Thus, the advanced rational design that relies on misincorporation of artificial
amino acids to create proteins with novel features relies on our ability to reengineer the AARS
synthetic and editing pathways that act as powerful gatekeepers of the canonical amino acid
alphabet.
References
[1] N. Cvetesic, A. Palencia, I. Halsz, S. Cusack and I Gruic-Sovulj, EMBO J, 33 (2014) 1639-53.
[2] N. Cvetesic, M. Semanjski, B. Soufi, K. Krug, I. Gruic-Sovulj and B. Macek, Sci Rep, 6 (2016) 28631.
[3] J.S.A Völler, M. Dulic and U.I. Gerling-Driessen, H. Biava, T. Baumann, N. Budisa, I. Gruic-Sovulj, B.
Koksch, ACS Central Science, 3 (2017)73-80.