Fig. 5.

Rare active fold-switched form of KaiB (fsKaiB) binds to the post-hydrolysis state of KaiC CI domain. a A 1.8-Å resolution structure of the KaiB_fs-cryst–CI_cryst complex (PDB 5JWO; from T. elongates). The ribbon diagram shows KaiB_fs-cryst in pink, CI_cryst in cyan, and bound ADP in yellow. Enclosed dotted box depicts the binding interface between KaiB_fs-cryst and CI_cryst. b Enlarged view of the KaiB_fs-cryst–CI_cryst complex binding interface depicting the interacting residues. c Structural comparison of KaiB ground state (gs) and fsKaiB: (i) KaiB^Te (gsKaiB; PDB 2QKE, subunit A) in green, KaiB_fs-cryst in pink; (ii) superposition of KaiB_fs-cryst in pink with N-SasA^Se (PDB 1T4Y; Se: S. elongatus) in cornflower blue. Residues K58, G89, and D91 are highlighted in yellow, red, and orange, respectively. d Comparison of the ATP binding site of the KaiB_fs-cryst–CI_cryst complex with ATP binding site of KaiC CI structures (from S. elongates) in the pre- and post-hydrolysis states: superposition of ADP-bound CI_cryst (cyan) with the CI^Se structure (green) in the (i) pre-ATP hydrolysis state (PDB 4TLC, subunit C) and (ii) post-ATP hydrolysis state (PDB 4TLA, subunit E)