Circular dichroism study of the interaction of glutamyl-tRNA synthetase with tRNAGlu2

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Abstract
The interaction of glutamyl-tRNA synthetase with tRNAGlu2 was studied [in Escherichia coli]. The enzyme was purified to apparent homogeneity and consists of a single chain with a MW of 59,000. The sedimentation coefficient (so20,w) was 3.7 S [Svedberg] and suggests this enzyme is asymmetric. The enzyme binds 1 mol of tRNAGlu2 and has a binding constant of 5 .times. 106 M-1 at pH 7.0 in 0.1 M NaCl. A circular dichroic study of the interaction under the same solvent conditions implied that the synthetase and tRNAGlu2 underwent a change in conformation as the complex was formed. In the case of the enzyme, there may be some loss of .alpha.-helical structure. The tRNAGlu2 results indicated a change in the conformation of > 1 of the helical regions of this molecule. A residue in the anticodon loop, 5-methylaminomethyl-2-thiouridine, has a distinct circular dichroic band at 340 nm in the free tRNAGlu2. As the complex is formed this band is shifted to the blue. This indicated that the enzyme forms an H bond with this residue in the anticodon loop, with a possible change in the conformation of the loop.

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