Compare the 3D structures of these two aminoacyl–tRNA synthetases. Each has its corresponding tRNA bound to it, as well as a bound ATP molecule. The first complex shown is that of glutaminyl–tRNA synthetase (GlnRS) from E. coli, and the second complex is aspartyl–tRNA synthetase (AspRS) from yeast. The ATPs are shown in space-filling mode. The tRNA may be alternatively displayed in 'Ball & Stick' form and 'CPK' (space-filling) form, and the protein may be alternatively displayed in 'CPK' and 'Cartoon' (ribbon) form. Toggle the "Hi-lite Protein" button in the Interface section of the control panel to color the protein residues in contact with the tRNA green and the "Hi-lite tRNA" button to color the tRNA residues in contact with the protein yellow.