The technique offers the advantage for tuning the concentration at which phase separation occurs ( Bracha et al., 2018). A second design, termed Corelets, uses a two-element modular design, which forms a multivalent core and acts as a seed which recruits phase separation-prone IDRs in response to blue light activation. Droplets are formed when the light stimulus is applied, and dissolve when removed. Photoactivation with blue light induces spatially-controlled and reversible formation of condensates in living cells ( Shin et al., 2017). The OptoDroplets design fuses the dimerization domain of the photoactivatable Cry2 protein to the intrinsically disordered region (IDR) of a phase separation-prone protein. Several variations have been described by the Brangwynne lab thus far ( Fig. This oligomerization induces phase transition at the site of illumination. One family of optogenetic designs replaces the oligomerization domain of a phase separation-prone protein of a condensate scaffold molecule with a photoactivatable domain, which are fused in frame with a fluorescent protein reporter.
Optogenetic methods utilize engineered proteins that contain domains which undergo changes in response to light activation. Building upon modular domain design and by expanding peptide functionality, a variety of protein biomaterials have been engineered which serve as versatile platforms for studying and addressing various challenges in regenerative medicine. Analytical tools for characterizing the molecular and bulk properties of these materials are also discussed. This chapter describes the design, recombinant synthesis, and fabrication strategies for protein-engineered biomaterials for use in tissue engineering applications. This approach allows multiple functional domains to be encoded directly into the protein backbone, creating a plethora of biomaterials with tunable mechanical, biochemical, and biodegradation properties. A defining feature of such protein-engineered biomaterials is the precise control over macromolecular composition and function, made possible by modular peptide domain design and exact specification of the encoding DNA sequence. Protein-engineered biomaterials are designed and synthesized using recombinant protein technology and offer an alternative to both harvested natural biomaterials and synthetic polymeric biomaterials. Heilshorn, in Comprehensive Biomaterials II, 2017 Abstract
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