| Design strategy |
Most promising strategy to pursue?
natural photoreceptor available associating photoreceptors (Section Associating Photoreceptors and Optogenetic Applications) order-disorder transitions (Section Light-regulated Order-disorder Transitions) homologous exchange of sensor modules (Section Light-regulated Tertiary and Quaternary Structural Transitions)
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| Dynamic range |
Maximum activity difference dark vs. light? (Section Photoreceptor Fundamentals.)
maximize free energy perturbation ΔΔG by choice of photosensor/effector, by linker optimization, by mutagenesis, by use of oligomeric photoreceptors minimize specific activity of T state and maximize specific activity of R state, e.g., by choice of effector, by mutagenesis embed photoreceptor in signaling networks that amplify response
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| Genetic encoding |
Functional expression in situ?
codon optimization cell-type-specific promoters intracellular trafficking signals ensure chromophore supply, e.g., by resorting to photoreceptors that use retinal, flavin-nucleotide and biliverdin chromophores
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In situ activity |
Appropriate activity levels in situ?
adjust expression levels, especially for associating photoreceptors (Section Photoreceptor Fundamentals) vary specific activity by choice of effector module, by mutagenesis (e.g., attenuation of activity) embed photoreceptors in signaling networks for amplification of response
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| Light sensitivity |
Can photoreceptor be activated to sufficient extent in situ?
increase light power, improve light delivery use photoreceptors sensitive to long wavelengths at which light penetrates tissue more deeply embed photoreceptor in signaling networks for response amplification modulate effective light sensitivity at photostationary state by variation of dark-recovery kinetics (Section Photoreceptor Fundamentals)
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| Temporal resolution |
Are the response kinetics sufficiently fast?
accelerate on-kinetics by increasing light power, by signal amplification (so that activation of fewer photoreceptors accelerate off-kinetics by choice of photosensor, by speeding up dark-recovery reaction via mutagenesis, by speeding up downstream biological processes use photochromic photoreceptors for temporal depletion of signaling state (Section Photochromic Photoreceptors)
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| Spatial resolution |
How can spatial resolution be improved?
cell-type-specific expression and subcellular trafficking (Section Genetic Encoding) spatially restricted illumination use photochromic photoreceptors for spatial depletion of signaling state (Section Photochromic Photoreceptors)
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| Orthogonality |
Parallel use of several photoreceptors and fluorescent proteins?
selective excitation via spectral separation selective excitation via different light sensitivities selective excitation via different recovery kinetics use photochromic photoreceptors to counteract inadvertent cross-talk between excitation channels
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