High-resolution structure of eukaryotic Fibrillarin interacting with Nop56 amino-terminal domain

The Nop56–Nop1 complex undergoes structural changes upon interaction with other proteins. (A) Comparison of the high-resolution X-ray structure of Sc Nop1^83–327 in complex with the Sc Nop56 amino-terminal domain (left) and the same complex as part of the U3 snoRNP in the cryo-EM structure of the 90S preribosome solved at 3.8 Å resolution (PDB: 5WLC) (right). Highlighted are the two regions displaying conformational changes: region 1 comprises the eukaryotic-specific insertion between Nop56-β2 and β3 and region 2 comprises the Lys-rich loop between α4 and β4. (B) Different surface charge distributions in region 1 of Nop56^1–166 in the two structures of A. (C) The conformational changes in region 1 of the Nop56 amino-terminal domain within the 90S preribosome are induced by the binding to Sof1. (D) The conformational changes in the exposed Lys-rich loop in region 2 of the Nop56 amino-terminal domain within the 90S preribosome are induced by the binding to the 5′ ETS RNA. (E) Structural details of region 1 of Nop56^1–166 in the structure of the Nop1^83–327–Nop56^1–166 complex. (F) Detailed view of the conformational changes within region 1 of Nop56^1–166 upon interaction with Sof1 in the 90S preribosome structure. (G) Structural details of region 2 of Nop56^1–166 in the structure of the Nop1^83–327–Nop56^1–166 complex. (H) Structural details of region 2 of Nop56^1–166 interacting with the 5′ ETS RNA in the 90S preribosome.