THE CRYSTAL STRUCTURE OF PHENYLALANYL-tRNA SYNTHETASE FROM THERMUS THERMOPHILUS COMPLEXED WITH COGNATE tRNA^Phe. M. Safro¹, Y. Goldgur¹, L.Mosyak¹, L. Reshetnikova², O. Lavrik³, V. Ankilova³, Dept. of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel¹, Institute of Molecular Biology, Russian Academy of Sciences, Moscow, Russia², Novosibirsk Institute of Bioorganic Chemistry, Novosibirsk, 630090, Russia³

The crystal structure of phenylalanyl-tRNA synthetase from Thermus thermophilus (^ttnPheRS) has previously been determined at 2.9Å resolution (Mosyak et. al., 1995). Here we present the structure of ^ttPheRS complexed with cognate tRNA^Phe also from Thermus thermophilus. The crystals of the complex are of the same space group, P3₂21, and virtually the same unit cell parameters as for the native ^ttPheRS (Reshetnikova et al., 1993).

Surprisingly, all four subunits of heterodimeric ([[alpha]][[beta]])₂ ^ttPheRS participate in binding of the tRNA^Phe. Multisubunit interaction of this type had not been observed in synthetase tRNA complexes before and demonstrates the functional necessity for a heterodimeric organization of the molecule. The N-terminal domain of the [[alpha]]-subunit (1-85) which is disordered in the native ^ttPheRS crystals is stabilized by interactions with tRNA^Phe and becomes visible. The structure of the complex provides an answer to the question, which of the two possible candidates actually recognizes the anticodon: it is the C-terminal domain of the [[beta]]-subunit possessing the known RNA-binding fold. The conformational changes of the bound tRNA^Phe and numerous contacts with ^ttPheRS will be described.

1. Mosyak,L., Reshetnikova,L., Goldgur,Y., Delarue,M. and Safro,M. (1995), Nature Str. Biol., 2, 537-547.

2. Reshetnikova,L., Khodyreva,S., Lavrik, O., Ankilova,V., Frolow,F. and Safro,M. (1993), J. Mol. Biol., 231, 927-929