NMR analyses of the conformations of L-isoleucine and L-valine bound to Escherichia coli isoleucyl-tRNA synthetase
The 400-MHz /sup 1/H NMR spectra of L-isoleucine and L-valine were measured in the presence of Escherichia coli isoleucyl-tRNA synthetase (IleRS). Because of chemical exchange of L-isoleucine or L-valine between the free state and the IleRS-bound state, a transferred nuclear Overhauser effect (TRNOE) was observed among proton resonances of L-isoleucine or L-valine. However, in the presence of isoleucyl adenylate tightly bound to the amino acid activation site of IleRS, no TRNOE for L-isoleucine or L-valine was observed. This indicates that the observed TRNOE is due to the interaction of L-isoleucine or L-valine with the amino acid activation site of IleRS. The conformations of these amino acids in the amino acid activation site of IleRS were determined by the analyses of time dependences of TRNOEs and TRNOE action spectra. The IleRS-bound L-isoleucine takes the gauche/sup +/ form about the C/sub ..cap alpha../-C/sub ..beta../ bond and the trans form about the C/sub ..beta../-C/sub ..gamma../sub 1// bond. The IleRS-bound L-valine takes the guache/sup -/ form about the C/sub ..cap alpha../-C/sub ..beta../ bond. Thus, the conformation of the IleRS-bound L-valine is the same as that of IleRS-bound L-isoleucine except for the delta-methyl group. The side chain of L-isoleucine or L-valine lies in an aliphatic hydrophobic pocket of the active site of IleRS. Such hydrophobic interaction with IleRS is more significant for L-isoleucine than for L-valine. The TRNOE analysis is useful for studying the amino acid discrimination mechanism of aminoacyl-tRNA synthetases.
- Research Organization:
- Univ. of Tokyo, Japan
- OSTI ID:
- 5599461
- Journal Information:
- Biochemistry; (United States), Vol. 26:20
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
LEUCINE
NMR SPECTRA
LIGASES
MOLECULAR STRUCTURE
VALINE
CHEMICAL SHIFT
DOSE-RESPONSE RELATIONSHIPS
ESCHERICHIA COLI
FLUORESCENCE
HEAVY WATER
NUCLEAR MAGNETIC RESONANCE
PROTONS
TRANSFER RNA
AMINO ACIDS
BACTERIA
BARYONS
CARBOXYLIC ACIDS
ELEMENTARY PARTICLES
ENZYMES
FERMIONS
HADRONS
HYDROGEN COMPOUNDS
LUMINESCENCE
MAGNETIC RESONANCE
MICROORGANISMS
NUCLEIC ACIDS
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
RESONANCE
RNA
SPECTRA
WATER
550601* - Medicine- Unsealed Radionuclides in Diagnostics