Tyrosyl-tRNA synthetase forms a mononucleotide-binding fold |
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Authors: | TN Bhat DM Blow P Brick J Nyborg |
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Institution: | Blackett Laboratory, Imperial College London, SW7 2BZ, England;Division of Biostructural Chemistry University of Aarhus DK-8000 Aarhus C, Denmark |
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Abstract: | Tyrosyl-tRNA synthetase from Bacillus stearothermophilus is a dimeric molecule of approximately 90,000 Mr. The crystal structure originally reported by Irwin et al. (1976) has been re-interpreted using a new density-modification technique. The reinterpretation is confirmed by the complete amino acid sequence (D. Barker & (G. Winter, personal communication). The structure consists of an amino-terminal domain, a domain containing five α-helices, and a region of 99 amino acids at the carboxyl terminus, which appears to be disordered. The re-interpretation reveals two new α-helices in the domain, and some changes in chain connections. The strands of the β-sheet are in the order A, F, E, B, C, D, with A antiparallel to the others. The arrangement of strands B to F is topologically identical to arrangements found in many other proteins, including the first five strands of the sheet in the NAD-binding domain of the dehydrogenases. Strands B, C, D form a mononucleotide-binding fold.In the complex with tyrosyl adenylate (Rubin & Blow, 1981), an intermediate in the reaction catalysed by the enzyme, the adenine lies near the carboxyl-terminal end of strand F of the β-sheet, with the ribose between the ends of strands B and E. This is similar to the nicotinamide position in dehydrogenases. The tyrosine moiety occupies a pocket at one side of the sheet, close to strands B and C. This tyrosine orientation is quite different from any part of the coenzyme in dehydrogenases. The ends of strands C and D of the sheet are buried, and binding of a nucleotide to the mononucleotide-binding fold formed by strands B, C, D would require a substantial structural change. |
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Keywords: | TyrRS tyrosyl-transfer RNA synthetase MetRS methionyl-tRNA synthetase AlaRS alanyl-tRNA synthetase |
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