Involved in the non-oxidative decarboxylation and detoxification of phenolic derivatives under anaerobic conditions (PubMed:24193968, PubMed:15979273). Flavin prenyltransferase that catalyzes the synthesis of the prenylated FMN cofactor (prenyl-FMN) for phenolic acid decarboxylase (By similarity). dimethylallyl phosphate + FMNH2 = phosphate + prenyl-FMNH2 Homododecamer. By 4-hydroxybenzoate and 3,4-dihydroxybenzoate. It is not known, if phenolic acid decarboxylase forms a complex composed of ShdB, ShdC and ShdD. The term subunit is often used in reference to the operon, however there is no experimental evidence to prove the existence of the complex. Belongs to the UbiX/PAD1 family. YclB subfamily.