Establishing the Fatty Acid Photodecarboxylase Cv FAP as a Platform for Photobiocatalytic Radical Transformations

Abstract The fatty acid photodecarboxylase from Chlorella variabilis (CvFAP) has emerged as a versatile photoenzyme for radical generation from readily available carboxylic acids. Here, we demonstrate that CvFAP can be repurposed as a platform for diverse photobiocatalytic transformations beyond its native decarboxylation activity. Using engineered variants, including Y466A, we establish four distinct classes of reactivity: (i) the intermolecular Giese-type coupling of fatty acids with cycloalkenones, (ii) the intramolecular decarboxylative radical cyclization via nucleophilic radicals and isolated C═C bonds of the same philicity, (iii) a cysteine-mediated (Z) → (E) photoisomerization of unsaturated fatty acids, and (iv) a radical carbohydroxylation reaction that demonstrates the enzyme’s capability of olefin bis-functionalization. Directed evolution further improves the catalytic performance for intramolecular cyclization, highlighting the tunability of CvFAP toward selective radical pathways. Computational analyses provide insight into substrate positioning and the origins of reactivity, supporting a model in which active-site engineering modulates competition between radical coupling and the native proton-coupled electron transfer pathway. Overall, this work establishes CvFAP as a broadly applicable scaffold for non-native photobiocatalytic transformations and expands the scope of enzymatic radical chemistry.