Figure 1.

The overall structure of heterotetrameric EcGlyRS. (A) The domain organization of EcGlyRS. To facilitate crystallization, the C-terminal part of the anticodon binding domain was truncated, resulting in the construct named EcGlyRS575. (B) Cartoon representation of the overall structure of (αβ)₂ heterotetrameric EcGlyRS575. The protomer consisting of chains B and D are colored as shown in Figure. 1A, while the other protomer (chains A and C) are colored gray. The glycine, Mg²⁺, and ATP analog (AMP-PNP) are shown as sphere models in the two aminoacylation pockets. Two protomers are organized through a noncrystallographic 2-fold axis to form the functional heterotetramer. (C) The topology diagram of the α- and β-subunits is colored as depicted in Figure 1A. Arrows represent β-strands, while α- and 3₁₀-helices are shown as cylinders. Class II signature motifs 1, 2 and 3 in the α-subunit are highlighted in salmon, yellow and blue, respectively, and the residues Arg326 and Asp329 in the β-subunit B3 domain contributing to ATP binding are labeled.