Concerted KaiC phosphorylation despite independent monomer dynamics

Determine why the cyanobacterial KaiABC oscillator exhibits a robust concerted phosphorylation–dephosphorylation cycle at the KaiC hexamer level, given that individual KaiC monomers can independently phosphorylate.

Background

The KaiABC system underlies the circadian clock in cyanobacteria, where KaiC hexamers display a global, ordered phosphorylation cycle that is robust and coherent across monomers.

Although monomers can phosphorylate independently, experiments show coordinated, system-wide cycling. The review proposes a topological mechanism as a possible solution, but the underlying reason for this concerted behavior remains explicitly stated as unclear in the caption text.