Thermostable valyl‐tRNA, isoleucyl‐tRNA and methionyl‐tRNA synthetases from an extreme thermophile Thermus thermophilus HB8: protein structure and Zn2+ binding

Abstract
Thermostable valyl‐tRNA, isoleucyl‐tRNA and methionyl‐tRNA synthetases have been purified from an extreme thermophile, Thermus thermophilus HB8. Valyl‐tRNA and isoleucyl‐tRNA synthetases are found to be monomer proteins (M r 108000 and 129000, respectively), while methionyl‐tRNA synthetase is a dimer protein (M r 150000). These enzymes are very similar with respect to amino acid compositions and α‐helix contents as estimated by circular dichroism analyses. Furthermore, two Zn2+ are tightly bound to each of these synthetases. These data suggest that valyl‐tRNA and isoleucyl‐tRNA synthetases consist of two domains, each corresponding to the subunit of methionyl‐tRNA synthetase.

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