Conformational flexibility of tRNA: structural changes in yeast tRNA(Asp) upon binding to aspartyl-tRNA synthetase.

The availability of several X-ray structures at atomic resolution of tRNA(Asp) from yeast, both in its free state and complexed with its cognate tRNA-synthetase, enables a detailed examination of the conformational changes due to interaction with the enzyme. Although the molecule conserves its general L shape, its conformation undergoes important modifications. They may be described as a bending of the two arms which brings the 3' acceptor end and the anticodon part closer together, completed by a drastic change of the anticodon loop, which puts the anticodon bases in a more exposed position, facilitating their interaction with the synthetase. The packing interactions in the crystals are also discussed. Finally, the results of protection studies by chemical probes in solution are discussed in view of the RNA-protein contacts observed in the crystals.