Fig. 4
From: Circadian oscillator proteins across the kingdoms of life: structural aspects
Crystal structures of cyanobacterial clock proteins KaiC, KaiA, and KaiB. a Side view of the KaiC hexamer (PDB 2GBL) with 12 ATP (magenta) binding sites. b KaiA dimer (PDB 1R8J). c KaiB tetramer (PDB 1WWJ). d KaiC monomer with CI and CII domains and the S-shaped loop. e Structure showing two chains (A and B) of the hexameric KaiC depicting the key phosphorylation site—Ser431 and Thr432—and the bound ATP at the subunit–subunit interface. On the right is a detailed view of the interface showing the glutamates close to ATP that help to activate phosphorylation