Crystal structures of an unmodified bacterial tRNA reveal intrinsic structural flexibility and plasticity as general properties of unbound tRNAs

Comparative structural analyses between the crystal structure of E. coli tRNA^Asp with other free tRNA molecules. (A,B) Conformational differences in the anticodon loop of the two molecules of E. coli tRNA^Asp that comprise the crystallographic asymmetric unit. (C,D) Conformational differences in the D loop of the two molecules of E. coli tRNA^Asp that comprise the crystallographic asymmetric unit. (E–H) The core region of the two molecules of unmodified E. coli tRNA^Asp that comprise the crystallographic asymmetric unit is very similar in conformation to the core region of both modified yeast tRNA^Asp (PDB ID: 1VTQ) (Comarmond et al. 1986) and yeast tRNA^Phe (PDB ID: 1EHZ) (Shi and Moore 2000), whereas the core region of an unmodified E. coli tRNA^Phe (PDB ID: 3L0U) (Byrne et al. 2010) is comparatively different (m²G and m²₂G represent 2-methylguanosine and N²,N²-dimethylguanosine, respectively). In the latter structure, the extruded U45 forms a crystal lattice contact and is replaced by U45 from a symmetry related molecule (yellow).