Description

None of the 20 canonical amino-acid side chains contains a built-in photoswitchable chromophore that undergoes clean, reversible light-driven isomerization the way synthetic photoswitches do. Yet, photoswitchable ncAAs play a crucial role in engineering light sensitivity in enzymes. Here, we highlight authors who went on a crusade to expand the photoswitchable ncAA repertoire for the recombinant production of photocontrolled enzymes using azobenzene, arylazopyrazole, arylazothiazole, hemithioindigo, and spiropyran photoswitch scaffolds.

Now let's dream about broader applications of photoswitchable ncAAs: biotherapy with enzymes that activate only where and when you shine light; biocatalysis: light-controlled enzymes could transform drug synthesis and biofuel production. This work pushes ncAAs into dynamic, reversible control.

Citation: Hiefinger et al., 2025

Photoswitchable non-canonical amino acids contain chromophore groups that change conformation reversibly in response to light. None of the 20 standard amino acids offer this capability. By incorporating photoswitch ncAAs at defined sites in enzymes, researchers can turn catalytic activity on and off with light.

A 2025 study expanded the available photoswitchable ncAA toolkit to include five scaffold types: azobenzene, arylazopyrazole, arylazothiazole, hemithioindigo, and spiropyran. Each offers different wavelength sensitivities, switching speeds, and thermal stability profiles, giving enzyme engineers a spectrum of control options (Hiefinger et al., 2025).

The therapeutic potential is significant: enzymes that activate only at a specific tissue when illuminated, reducing systemic side effects. In biocatalysis, light-controlled enzymes could enable reaction switching without changing temperature or reagents. This represents a fundamentally new category of protein functionality, one that only ncAAs can provide.

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