Reports

Ammonia Channel Couples Glutaminase with Transamidase Reactions in GatCAB

Akiyoshi Nakamura,^1* Min Yao,^1* Sarin Chimnaronk,^1,2 Naoki Sakai,¹ Isao Tanaka¹

The formation of glutaminyl transfer RNA (Gln-tRNA^Gln) differs among the three domains of life. Most bacteria employ an indirect pathway to produce Gln-tRNA^Gln by a heterotrimeric glutamine amidotransferase CAB (GatCAB) that acts on the misacylated Glu-tRNA^Gln. Here, we describe a series of crystal structures of intact GatCAB from Staphylococcus aureus in the apo form and in the complexes with glutamine, asparagine, Mn²⁺, and adenosine triphosphate analog. Two identified catalytic centers for the glutaminase and transamidase reactions are markedly distant but connected by a hydrophilic ammonia channel 30 Å in length. Further, we show that the first U-A base pair in the acceptor stem and the D loop of tRNA^Gln serve as identity elements essential for discrimination by GatCAB and propose a complete model for the overall concerted reactions to synthesize Gln-tRNA^Gln.

¹ Faculty of Advanced Life Sciences, Hokkaido University, Sapporo 060-0810, Japan.
² Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, Nakornpathom 73170, Thailand.

^* These authors contributed equally to this work.

To whom correspondence should be addressed. E-mail: tanaka{at}castor.sci.hokudai.ac.jp

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Dual-targeted tRNA-dependent amidotransferase ensures both mitochondrial and chloroplastic Gln-tRNAGln synthesis in plants.

C. Pujol, M. Bailly, D. Kern, L. Marechal-Drouard, H. Becker, and A.-M. Duchene (2008)
PNAS 105, 6481-6485
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From one amino acid to another: tRNA-dependent amino acid biosynthesis.

K. Sheppard, J. Yuan, M. J. Hohn, B. Jester, K. M. Devine, and D. Soll (2008)
Nucleic Acids Res. 36, 1813-1825
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The Helicobacter pylori Amidotransferase GatCAB Is Equally Efficient in Glutamine-dependent Transamidation of Asp-tRNAAsn and Glu-tRNAGln.

K. Sheppard, P.-M. Akochy, J. C. Salazar, and D. Soll (2007)
J. Biol. Chem. 282, 11866-11873
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Deinococcus glutaminyl-tRNA synthetase is a chimer between proteins from an ancient and the modern pathways of aminoacyl-tRNA formation.

M. Deniziak, C. Sauter, H. D. Becker, C. A. Paulus, R. Giege, and D. Kern (2007)
Nucleic Acids Res. 35, 1421-1431
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A single tRNA base pair mediates bacterial tRNA-dependent biosynthesis of asparagine.

M. Bailly, S. Giannouli, M. Blaise, C. Stathopoulos, D. Kern, and H. D. Becker (2006)
Nucleic Acids Res. 34, 6083-6094
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Emergence of the universal genetic code imprinted in an RNA record.

M. J. Hohn, H.-S. Park, P. O'Donoghue, M. Schnitzbauer, and D. Soll (2006)
PNAS 103, 18095-18100
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