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. Author manuscript; available in PMC: 2020 Aug 1.
Published in final edited form as: IUBMB Life. 2019 Jun 13;71(8):1088–1098. doi: 10.1002/iub.2094

Figure 5. Interactions of Class I aaRS with the phosphate group of the 3’-terminal adenosine.

Figure 5

The hairpin structure of Class I isoaccepting tRNA substrates orients this phosphate group so that it points toward the N-terminus of the specificity-determining helix (purple). Hydrogen bond distances shown suggest that, except in the case of 5OMW_LeuRS, these interactions may be strong. In 1F7U_ArgRS, the interaction is reinforced by a salt bridge between the phosphate group and R350. Specificity is enhanced by the stacking interaction between the nonpolar face of the A76 ribose and a conserved aromatic sidechain immediately following the four unpaired amide nitrogens at the N-terminus of the specificity-determining helix (yellow) (adapted from (4), with permission) (adapted from (4), with permission).