Yeast cytoplasmic and mitochondrial methionyl-tRNA synthetases: two structural frameworks for identical functions.
The yeast Saccharomyces cerevisiae possesses two methionyl-tRNA synthetases (MetRS), one in the cytoplasm and the other in mitochondria. The cytoplasmic MetRS has a zinc-finger motif of the type Cys-X(2)-Cys-X(9)-Cys-X(2)-Cys in an insertion domain that divides the nucleotide-binding fold into two halves, whereas no such motif is present in the mitochondrial MetRS. Here, we show that tightly bound zinc atom is present in the cytoplasmic MetRS but not in the mitochondrial MetRS. To test whether the presence of a zinc-binding site is required for cytoplasmic functions of MetRS, we constructed a yeast strain in which cytoplasmic MetRS gene was inactivated and the mitochondrial MetRS gene was expressed in the cytoplasm. Provided that methionine-accepting tRNA is overexpressed, this strain was viable, indicating that mitochondrial MetRS was able to aminoacylate tRNA(Met) in the cytoplasm. Site-directed mutagenesis demonstrated that the zinc domain was required for the stability and consequently for the activity of cytoplasmic MetRS. Mitochondrial MetRS, like cytoplasmic MetRS, supported homocysteine editing in vivo in the yeast cytoplasm. Both MetRSs catalyzed homocysteine editing and aminoacylation of coenzyme A in vitro. Thus, identical synthetic and editing functions can be carried out in different structural frameworks of cytoplasmic and mitochondrial MetRSs.
Senger
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B
UPR n degrees 9002 du CNRS, Institut de Biologie Moléculaire et Cellulaire du CNRS, 15, rue René Descartes, Strasbourg Cedex, 67084, France.
Despons
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L
Walter
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P
Jakubowski
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H
Fasiolo
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F
D000215:Acylation; D000595:Amino Acid Sequence; D001665:Binding Sites; D003065:Coenzyme A / Q000378:metabolism; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000201:enzymology*; D005800:Genes, Fungal / Q000235:genetics; D005816:Genetic Complementation Test; D006710:Homocysteine / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008715:Methionine / Q000378:metabolism; D008718:Methionine-tRNA Ligase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D021381:Protein Transport; D012358:RNA, Transfer, Met / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D015032:Zinc / Q000378:metabolism; D016335:Zinc Fingers / Q000235:genetics / Q000502:physiology
D012358:RNA, Transfer, Met; D006710:Homocysteine; D008715:Methionine; D008718:Methionine-tRNA Ligase; D015032:Zinc; D003545:Cysteine; D003065:Coenzyme A