1. a | Schematic phylogenetic tree based on the amino acid alignments of conserved middle (MID) and P-element induced wimpy testis (PIWI) domains from eukaryotic Argonaute proteins (eAgos) and prokaryotic Argonaute proteins (pAgos). b | The crystal structure of human Argonaute 2 (hAgo2; RCSB Protein Data Bank (PDB) entry 4Z4C), indicated as eAgo (left). The crystal structure of Thermus thermophilus Argonaute (TtAgo; PDB entry 3F73), indicated as pAgo (middle). Both structures have the conserved bi-lobed scaffold between eAgos and pAgos. Ternary complex of TtAgo (rotated 90° compared with the structure shown in the middle) with a small interfering DNA (siDNA) guide (red) bound to an RNA target (blue) (PDB entry 3F73) (right)21. All of the distinct protein domains are shown in different colours (MID in yellow, PAZ (PIWI–Argonaute–Zwille) in purple, amino-terminal domain (N) in cyan, PIWI in green, and linker domains L1 and L2 in grey). AaAgo, Aquifex aeolicus Argonaute; AfAgo, Archaeoglobus fulgidus Argonaute; MjAgo, Methanocaldococcus jannaschii Argonaute; MkAgo, Methanopyrus kandleri Argonaute; MpAgo, Marinitoga piezophila Argonaute; NgAgo, Natronobacterium gregoryi Argonaute; PfAgo, Pyrococcus furiosus Argonaute; RsAgo, Rhodobacter sphaeroides Argonaute; TpAgo, Thermotoga profunda Argonaute; WAGO, worm-specific Argonaute; PIWI-RE, PIWI domain-containing protein with conserved R and E residues. Part a is adapted with permission from Ref. 4, Macmillan Publishers Limited.
FIGURE 1a is modified from (REF. 4) Swarts, D. C. et al.
The evolutionary journey of Argonaute proteins. Nat. Struct. Mol. Biol. 21, 743–753 (2014).