Engineering Adaptable Materials via crosslinking by Circadian Clock Proteins

Circadian oscillators exist in nearly all living organisms to regulate sleep cycles, metabolism and, in the case of cyanobacteria, the timing of photosynthesis. The cyanobacteria circadian clock involves the cyclic binding and unbinding of monomeric KaiB proteins to hexameric KaiC rings over a regular 24-hour cycle. Here, we exploit this system to enable time-dependent aggregation and gelation of colloids in suspension. Specifically, we coat colloids with KaiB proteins such that KaiC rings act as crosslinkers to connect and cluster colloids via time-varying binding to KaiB. We use fluorescence microscopy and sedimentation experiments to show that mutant KaiC proteins that are frozen in the 'KaiB-binding' state lead to large scale percolated structures of colloidal aggregates that continue to slowly grow over several days. Conversely, with non-binding KaC mutants, the materials remain as diffuse suspensions of single colloids. Wild-type KaiC proteins lead to time-varying crosslinking and aggregation that is controlled by the phosphorylation state of KaiC. We build on this work by demonstrating that this platform can enable time-varying material properties that span from the microscopic to macroscopic scale and can be easily incorporated into synthetic and biological materials for potential applications in pharmaceuticals and adaptive bio-inspired infrastructure.