The family of berberine bridge enzyme-like enzymes: A treasure-trove of oxidative reactions

Abstract

Biological oxidations form the basis of life on earth by utilizing organic compounds as electron donors to drive the generation of metabolic energy carriers, such as ATP. Oxidative reactions are also important for the biosynthesis of complex compounds, i.e. natural products such as alkaloids that provide vital benefits for organisms in all kingdoms of life. The vitamin B-derived cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) enable an astonishingly diverse array of oxidative reactions that is based on the versatility of the redox-active isoalloxazine ring. The family of FAD-linked oxidases can be divided into subgroups depending on specific sequence features in an otherwise very similar structural context. The sub-family of berberine bridge enzyme (BBE)-like enzymes has recently attracted a lot of attention due to the challenging chemistry catalyzed by its members and the unique and unusual bi-covalent attachment of the FAD cofactor. This family is the focus of the present review highlighting recent advancements into the structural and functional aspects of members from bacteria, fungi and plants. In view of the unprecedented reaction catalyzed by the family's namesake, BBE from the California poppy, recent studies have provided further insights into nature's treasure chest of oxidative reactions.

Discovery of key regulators of dark gland development and hypericin biosynthesis in St. John's Wort (Hypericum perforatum)

“…To our knowledge, no experimental proof of the functionality of the PR‐10‐related POCPs exists, but a PR‐10‐related protein has been shown to exhibit norcoclaurine synthase activity in opium poppy by performing a condensation reaction between dopamine and 4‐hydroxyphenylacetaldehyde in benzylisoquinoline alkaloid synthesis (Lee and Facchini, ). Besides the POCP genes, we identified a berberine bridge enzyme (BBE; cluster 2, Daniel et al ., ), which suggests an additional or alternative function to POCPs for the formation of one of the three C‐C linkages between the naphthodianthrone halves of hypericin. Since the encoded BBE is targeted for secretion by a N‐terminal signal peptide (Käll et al ., ), it will most likely close the last C‐C bond for which an enzyme is required, similar to THCS and CBDS in tetraketide‐based cannabinoid synthesis (Sirikantaramas et al ., ; Taura et al ., ), which belong to the same protein family and are predicted to contain N‐terminal signal peptides as well.…”

Identification and Characterization of Citrus Peel Uronic Acid Oxidase

“…Plant carbohydrate oxidases belong to the berberine bridge enzyme (BBE) family, a functionally diverse family of oxidases containing a bicovalently attached flavin adenine dinucleotide (FAD) cofactor . BBE proteins belong to a larger family of flavoenzymes with a VAO/PCMH fold, distinct from carbohydrate oxidases belonging to the glucose‐methanol‐choline oxidoreductase (GMC) family of flavoenzymes.…”

“…Like other structurally characterized eukaryotic BBE enzymes, UAO contains two conserved N‐terminal Cys residues (C45 and C108) putatively involved in disulfide formation (Figure ). As a member of the BBE family, UAO contains a conserved Cys and His residue (C185 and H123) for bicovalent attachment of FAD (Figure ). In this family, enzyme‐catalyzed substrate oxidation is accompanied by FAD reduction .…”

“…As a member of the BBE family, UAO contains a conserved Cys and His residue (C185 and H123) for bicovalent attachment of FAD (Figure ). In this family, enzyme‐catalyzed substrate oxidation is accompanied by FAD reduction . Re‐oxidation of FAD by O 2 generates H 2 O 2 , and completes the catalytic cycle.…”

“…Re‐oxidation of FAD by O 2 generates H 2 O 2 , and completes the catalytic cycle. BBE enzymes generally accommodate large substrates (e.g., carbohydrate oligomers), and bicovalent attachment of FAD is thought to modulate its reduction potential, and to facilitate optimal orientation of the flavin cofactor in the large active site cavity . The recombinant UAO was successfully obtained by secreted expression in P. pastoris , and TALON Co 2+ ‐affinity purification (Figure A, see details in the Supporting Information).…”