Fig. 5: Binding of bile acid derivatives disrupts σNS oligomerization and RNA-destabilizing activity.

a Electrostatic representation of σNS-R6A in complex with bile acid derivatives (S1 and S2), colored in green. The grey-dotted box demarcates the missing disordered N-terminal arm. b, c Residues mediating bile acid-derivative binding at S1 and S2 defined by LigPlot following the same notations as in Fig. 4e for hydrophobic and hydrogen bond interactions. Bile acid derivatives are shown in purple bonds with carbon and oxygen atoms in black and red, respectively. c The higher-order structure formed by crystal packing of σNS-R6A when bile acid derivatives are present. d The helical assembly as observed in the crystal structure of Se-Met σNS-R6A with dimeric subunits shown in pink and blue. e Close-up view of the N-terminal arm (pink) interacting with a groove in the neighboring subunit (blue). f In the structure of σNS-R6A in complex with bile acid derivatives, the same groove is occupied by a bile acid replacing the N-terminal arm, which becomes disordered. g Electrostatic representations σNS-ΔN17 in complex with two bile acid derivatives (in green) bound at the same location as in the σNS-R6A structure shown in Fig. 5a. The grey-dotted box demarcates the missing N-terminal arm.