X-ray Structures of the Signal Recognition Particle Receptor Reveal Targeting Cycle Intermediates
Figure 3
Structural adaptations in the active site upon nucleotide binding.
(A) Asp258 is shown to progressively coordinate the nucleotide from the apo state to the Ffh-NG complex state. In F2 (magenta), the nucleotide is not coordinated by Asp258. In F1 (blue) the nucleotide is within weak coordinating distance to Asp258. In FtsY from the Ffh complex (green), Asp 258 coordinates the nucleotide (hydrogen bonds shown as dotted lines). (B) IBD residue Arg142 is shown to coordinate the magnesium ion and interact with the γ-phosphate in the complex form of FtsY (green). In F1 (blue) and F2(magenta), the ‘DTFRAGA’ motif unfolds and positions Arg142 out of the active site and away from interaction with the bound nucleotide. (C) In complex with Ffh-NG (green), the FtsY sidechains of Arg 195 and Asn111 are positioned out of the active site and away from the γ phosphate. In F1 (blue) and F2 (magenta), both Arg195 and Asn111 rotate towards the γ phosphate and the amino moiety of Asn111, now coordinating the γ phosphate in a non-canonical position.