Three‐dimensional structure of phenylalanyl‐transfer RNA synthetase from Thermus thermophilus HB8 at 0.6‐nm resolution

Publisher Website
Google Scholar
Abstract
The three‐dimensional structure of the heterodimeric α2β2 enzyme phenylalanyl‐tRNA synthetase from Thermus thermophilus HB8 has been determined by X‐ray crystallography, using the multiple‐isomorphous‐replacement method at 0.6 nm resolution. Trigonal crystals of space group P3221 have cell dimensions a=b= 17.6 nm and c= 14.2 nm. Assuming one heterodimeric molecule/asymmetric unit, the ratio of unit cell volume/molecular mass was V= 0.00244 nm3/Da, which is in the middle of the range normally observed. However, after a rotation‐function calculation and measurement of the density of the native crystals, we postulate the existence of only the αβ dimer in the asymmetric units. This implies 73% solvent content in the unit cell. Three heavy‐atom derivatives [K2PtCl4, KAu(CN)2 and Hg(CH3COO)2] and the solvent‐flattening procedure were used for electron‐density‐map calculations. This map confirmed our hypothesis and revealed a remarkably large space filled by solvent, with αβ dimer only in the asymmetric unit. The phenylalanyl‐tRNA synthetase from T. thermophilus molecule has a ‘quasi‐linear’ subunit organization. As can be concluded at this level of resolution, there is no contact between small α subunits in the functional heterodimer.

This publication has 18 references indexed in Scilit: