Purification and functional characterization of the Glu-tRNAGln amidotransferase from Chlamydomonas reinhardtii

Dieter Jahn, Young Chang Kim, Yoshizumi Ishino, Min Wei Chen, Dieter Söll

Research output: Contribution to journalArticle

34 Citations (Scopus)

Abstract

The formation of glutaminyl-tRNA (Gln-tRNA) in Bacilli, chloroplasts, and mitochondria occurs in a two-step reaction. This involves misacylation of tRNAGln with glutamate by glutamyl-tRNA synthetase and subsequent amidation of Glu-tRNAGln to the correctly acylated Gln-tRNAGln by a specific amidotransferase (Schön, A., Kannangara, C. G., Gough, S., and Söll, D. (1988) Nature 331, 187-190). Here we demonstrate the existence of this pathway in green algae and describe the purification of the Glu-tRNAGln amidotransferase from Chlamydomonas reinhardtii. The purified enzyme showed an Mr of approximately 120,000 when analyzed by glycerol gradient sedimentation and gel filtration. An apparent Mr of 63,000 of the denatured protein was demonstrated by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. This indicates that the enzyme possesses an α2 structure. The substrate for the purified enzyme is Glu-tRNAGln but not Glu-tRNAGlu. The enzyme requires ATP, Mg2+, and an amide donor for the conversion. Acceptable amide donors are glutamine, asparagine, and ammonia. Blocking of the glutamine-dependent reaction by alkylation of the protein with 6-diazo-5-oxonorleucine did not inhibit the ammonia-dependent reaction, suggesting that the enzyme has separate glutamine and ammonia binding sites. As suggested by Wilcox (Wilcox, M. (1969) Eur. J. Biochem. 11, 405-412) the amidation reaction may involve glutamyl-phosphate formation, since ATP is cleaved to ADP when the enzyme is incubated with Glu-tRNAGln and ATP. In common with other glutamine amidotransferases, the enzyme also possesses low glutaminase activity. The purified Glu-tRNAGln amidotransferase forms a stable complex with Glu-tRNAGln in the presence of ATP and Mg2+ but in the absence of the amide donor as determined by gradient centrifugation.

Original languageEnglish
Pages (from-to)8059-8064
Number of pages6
JournalJournal of Biological Chemistry
Volume265
Issue number14
Publication statusPublished - May 15 1990
Externally publishedYes

Fingerprint

RNA, Transfer, Gln
Chlamydomonas reinhardtii
Purification
Glutamine
Enzymes
Adenosine Triphosphate
Ammonia
Amides
Glutamate-tRNA Ligase
RNA, Transfer, Glu
Glutaminase
Chlorophyta
Mitochondria
Centrifugation
Asparagine
Alkylation
Bacilli
Chloroplasts
Algae
Transfer RNA

All Science Journal Classification (ASJC) codes

  • Biochemistry

Cite this

Purification and functional characterization of the Glu-tRNAGln amidotransferase from Chlamydomonas reinhardtii. / Jahn, Dieter; Kim, Young Chang; Ishino, Yoshizumi; Chen, Min Wei; Söll, Dieter.

In: Journal of Biological Chemistry, Vol. 265, No. 14, 15.05.1990, p. 8059-8064.

Research output: Contribution to journalArticle

Jahn, Dieter ; Kim, Young Chang ; Ishino, Yoshizumi ; Chen, Min Wei ; Söll, Dieter. / Purification and functional characterization of the Glu-tRNAGln amidotransferase from Chlamydomonas reinhardtii. In: Journal of Biological Chemistry. 1990 ; Vol. 265, No. 14. pp. 8059-8064.
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AB - The formation of glutaminyl-tRNA (Gln-tRNA) in Bacilli, chloroplasts, and mitochondria occurs in a two-step reaction. This involves misacylation of tRNAGln with glutamate by glutamyl-tRNA synthetase and subsequent amidation of Glu-tRNAGln to the correctly acylated Gln-tRNAGln by a specific amidotransferase (Schön, A., Kannangara, C. G., Gough, S., and Söll, D. (1988) Nature 331, 187-190). Here we demonstrate the existence of this pathway in green algae and describe the purification of the Glu-tRNAGln amidotransferase from Chlamydomonas reinhardtii. The purified enzyme showed an Mr of approximately 120,000 when analyzed by glycerol gradient sedimentation and gel filtration. An apparent Mr of 63,000 of the denatured protein was demonstrated by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. This indicates that the enzyme possesses an α2 structure. The substrate for the purified enzyme is Glu-tRNAGln but not Glu-tRNAGlu. The enzyme requires ATP, Mg2+, and an amide donor for the conversion. Acceptable amide donors are glutamine, asparagine, and ammonia. Blocking of the glutamine-dependent reaction by alkylation of the protein with 6-diazo-5-oxonorleucine did not inhibit the ammonia-dependent reaction, suggesting that the enzyme has separate glutamine and ammonia binding sites. As suggested by Wilcox (Wilcox, M. (1969) Eur. J. Biochem. 11, 405-412) the amidation reaction may involve glutamyl-phosphate formation, since ATP is cleaved to ADP when the enzyme is incubated with Glu-tRNAGln and ATP. In common with other glutamine amidotransferases, the enzyme also possesses low glutaminase activity. The purified Glu-tRNAGln amidotransferase forms a stable complex with Glu-tRNAGln in the presence of ATP and Mg2+ but in the absence of the amide donor as determined by gradient centrifugation.

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