Fig. 3. Structural rearrangements in IF2.

a Superimposition of the G-domain (gray) in structures I-A and II-A reveals domain rearrangements between extended (faded colors) and compact (darker colors) IF2. Domains C1 and C2 move by 29 Å and 35 Å, respectively. Inset: Overview of IF2 bound to the 70S-IC viewed in the same orientation. b Alignment of domain II in IF2 shows that helix H8 (green) bends by 25° and turns sharply by 90° around residue Leu⁶²⁵ to accommodate the displacement of domain C1. c, d Movement of domains C1 and C2 between the extended (gray) and compact (red or yellow) IF2 is accompanied by a rotation of 116° for domain C1 and 152° for domain C2. The displacement of corresponding Cα atoms is indicated. e, f Position of domain C1 relative to the G-domain in compact (e) and extended (f) IF2. In IF2-GDP, helix H10 of the C1 domain (yellow) faces the sw2-α-helix (tan) in the G-domain (magenta) (e), while in IF2-GDPCP helices H9 and H12 from the opposite side of domain C1 face the G-domain (f). g Rotation of the sw2-helical region by 65° in IF2-GDP forms the new interface with domain C1, displacing the catalytic His³⁹⁹ residue by more than 8 Å away from the nucleotide-binding pocket. h The conformation of sw2 in extended IF2-GDPCP (white) is not compatible with the location of domain C1 (yellow) in compact IF2-GDP.