Characterization of Fatty Acid Photodecarboxylase in Zeolitic Imidazolate Frameworks

Fatty acid photodecarboxylase (FAP) was recently discovered in microalgae and is a photoenzyme that harvests sunlight to convert long-chain fatty acids to hydrocarbons. The hydrophobicity of the substrates and photoproducts strongly affects the stability of FAP in vitro studies. Here, we incorporated zeolitic imidazole frameworks (ZIFs) as structural protecting cages and characterized Chlorella variabilis FAP (cvFAP) in ZIFs. Due to the preparation conditions and the surface properties, ZIFs with a hydrophobic surface (ZIF-8) form a cluster-like packed morphology, and ZIFs with a hydrophilic surface (ZIF-90) form a hexagon-like morphology. However, both ZIFs compress FAP and lead to a more hydrophobic active-site environment and fewer active-site water molecules. The ZIF-90 cages enhance the cvFAP activity at higher temperature conditions. Upon irradiation, FAP undergoes energy deactivation and photoinactivation, and these processes compete with each other. In both ZIF cages, the deactivation processes of the excited FAP are slightly enhanced, resulting from the bent cofactor conformation. Although the ZIFs provide protective confinement to stabilize the enzyme structures when structural destruction originates from molecular fragmentation casing by photoinduced radical reactions, such protective effects are limited.