Circadian clock proteins drive structural oscillations in colloidal fluids.

Abstract

Cyanobacteria rely on a circadian oscillator system of proteins, KaiA, KaiB and KaiC, to regulate a variety of cellular processes. Powered by ATP phosphorylation, KaiA and KaiB proteins alternately bind to KaiC, resulting in the cyclical assembly and disassembly of KaiC-KaiB complexes. By biotinylating KaiB monomers, we repurpose the KaiC-KaiB complexes to function as crosslinkers with unique time-dependent properties. To demonstrate the efficacy of these ‘circadian crosslinkers’, we design suspensions of streptavidin-coated colloids that exhibit time-dependent structural changes driven by the oscillatory assembly and disassembly of KaiB-KaiC complexes. Further, using fluorescence microscopy, image analysis and biochemical assays, we show that the rate, efficacy and oscillatory signature of crosslinking can be tuned by altering the phosphorylation state of KaiC. Our findings demonstrate that a model circadian oscillator can drive time-varying restructuring of abiotic colloidal suspensions, providing new biochemical machinery for developing self-directed, programmable, and reconfigurable biomaterials. This work may one day enable engineers to incorporate biochemical circadian clocks into future exosuits, infrastructure, and deep sea and space exploration equipment.