Curated Optogenetic Publication Database

Abstract: The robustness and broad applicability of an optogenetic tool depends heavily on the properties of the underlying photoreceptor protein and its cognate binding partner-the light-responsive 'core'. Current red light optogenetic systems for mammalian cells rely on phytochrome-based photoreceptors: large (70-kDa) proteins that act as dimers, enforcing dimerization on attached proteins. Naturally occurring or engineered binding partners can function effectively, but large size, complex interaction, background binding, weak affinity and modest dynamic range remain limiting. Here we developed a small (17-kDa) monomeric biliverdin-binding photoreceptor, FenixS, and a highly selective, high-affinity binder, Ash1 (6 kDa) using structure-based design and directed evolution. Negligible OFF-state binding and a >1,200-fold increase in binding affinity upon 700-nm illumination yield a high-performance, ultralow background core for diverse applications. A FenixS-Ash1-based optogenetic tool for red light activation of transcription in mammalian cells performs robustly without biliverdin supplementation, with head-to-head comparisons confirming its control of gene expression versus established tools.

Abstract: Light-inducible regulatory proteins are powerful tools to interrogate fundamental mechanisms driving cellular behavior. In particular, genetically encoded photosensory domains fused to split proteins can tightly modulate protein activity and gene expression. While light-inducible split protein systems have performed well individually, few multichromatic and orthogonal gene regulation systems exist in mammalian cells. The design space for multichromatic circuits is limited by the small number of orthogonally addressable optogenetic switches and the types of effectors that can be actuated by them. We developed a library of red light-inducible recombinases and directed patterned myogenesis in a mesenchymal fibroblast-like cell line. To address the limited number of light-inducible domains (LIDs) responding to unique excitation spectra, we multiplexed light-inducible recombinases with our "Boolean logic and arithmetic through DNA excision" (BLADE) platform. Multiplexed optogenetic tools will be transformative for understanding the role of multiple interacting genes and their spatial context in endogenous signaling networks.

Abstract: Protein dimerization systems controlled by red light with increased tissue penetration depth are a highly needed tool for clinical applications such as cell and gene therapies. However, mammalian applications of existing red light-induced dimerization systems are hampered by limitations of their two components: a photosensory protein (or photoreceptor) which often requires a mammalian exogenous chromophore and a naturally occurring photoreceptor binding protein typically having a complex structure and nonideal binding properties. Here, we introduce an efficient, generalizable method (COMBINES-LID) for creating highly specific, reversible light-induced heterodimerization systems independent of any existing binders to a photoreceptor. It involves a two-step binder screen (phage display and yeast two-hybrid) of a combinatorial nanobody library to obtain binders that selectively engage a light-activated form of a photoswitchable protein or domain not the dark form. Proof-of-principle was provided by engineering nanobody-based, red light-induced dimerization (nanoReD) systems comprising a truncated bacterial phytochrome sensory module using a mammalian endogenous chromophore, biliverdin, and light-form specific nanobodies. Selected nanoReD systems were biochemically characterized, exhibiting low dark activity and high induction specificity, and further demonstrated for the reversible control of protein translocation and activation of gene expression in mice. Overall, COMBINES-LID opens new opportunities for creating genetically encoded actuators for the optical manipulation of biological processes.