Circadian Clock Proteins Program Time-Dependent Materials

Cyanobacteria rely on a circadian oscillator system of proteins, KaiA, KaiB and KaiC, to regulate a variety of cellular processes. KaiA and KaiB proteins alternately bind to KaiC, resulting in the cyclical assembly and disassembly of KaiC-KaiB complexes powered by ATP phosphorylation. By biotinylating KaiB monomers, we repurpose the KaiC-KaiB complexes to crosslink microscopic constituents of materials with unique time-dependent patterns. We incorporate these 'circadian crosslinkers' into suspensions of hydrogel microspheres and biopolymer networks to drive time-dependent structural changes mediate by the time-dependent formation and disassembly of KaiB-KaiC complexes. We use fluorescence microscopy, image analysis and biochemical assays to show that the rate, efficacy and oscillatory signature of material crosslinking can be tuned by altering the phosphorylation state of KaiC. Moreover, we demonstrate the versatility of circadian crosslinkers to confer autonomous changes in the properties of diverse material platforms from abiotic hydrogels and colloids to cytoskeletal composites. We anticipate the broad use of circadian crosslinkers for developing self-directed, programmable, and reconfigurable materials for applications from smart exosuits to self-repairing infrastructure to time-released drug delivery and filtration.