The single berberine bridge enzyme homolog of Physcomitrella patens is a cellobiose oxidase. (19th April 2018)

• Record Type: Journal Article
• Authors: Toplak, Marina; Wiedemann, Gertrud; Ulićević, Jelena; Daniel, Bastian; Hoernstein, Sebastian N. W.; Kothe, Jennifer; Niederhauser, Johannes; Reski, Ralf; Winkler, Andreas; Macheroux, Peter
• Is Part Of: FEBS journal. Volume 285:Number 10(2018)
• Page Start: 1923
• Page End: 1943
• Publication Date: 2018-04-19
• Subjects: enzyme catalysis -- enzyme mechanism -- flavin adenine dinucleotide -- plant biochemistry -- protein structure; Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pathology, Molecular -- Periodicals; 572
• DOI: 10.1111/febs.14458
• Languages: English
• ISSNs: 1742-464X

Abstract

Abstract : The berberine bridge enzyme from the California poppy Eschscholzia californica ( Ec BBE) catalyzes the oxidative cyclization of ( S )‐reticuline to ( S )‐scoulerine, that is, the formation of the berberine bridge in the biosynthesis of benzylisoquinoline alkaloids. Interestingly, a large number of BBE‐ like genes have been identified in plants that lack alkaloid biosynthesis. This finding raised the question of the primordial role of BBE in the plant kingdom, which prompted us to investigate the closest relative of Ec BBE in Physcomitrella patens ( Pp BBE1), the most basal plant harboring a BBE‐ like gene. Here, we report the biochemical, structural, and in vivo characterization of Pp BBE1. Our studies revealed that Pp BBE1 is structurally and biochemically very similar to Ec BBE. In contrast to Ec BBE, we found that Pp BBE1 catalyzes the oxidation of the disaccharide cellobiose to the corresponding lactone, that is, Pp BBE1 is a cellobiose oxidase. The enzymatic reaction mechanism was characterized by a structure‐guided mutagenesis approach that enabled us to assign a catalytic role to amino acid residues in the active site of Pp BBE1. In vivo experiments revealed the highest level of PpBBE1 expression in chloronema, the earliest stage of the plant's life cycle, where carbon metabolism is strongly upregulated. It was also shown that the enzyme is secreted to the extracellular space, where it may be involved in later steps of cellulose degradation, thereby allowing the moss to make use of cellulose for energy production. Overall, our results suggest that the primordial role of BBE‐like enzymes in plants revolved around primary metabolic reactions in carbohydrate utilization. Database: Structural data are available in the PDB under the accession numbers6EO4 and6EO5 . Abstract : The structural, biochemical, and in vivo characterization of the single berberine bridge enzyme (BBE) homolog of Physcomitrella patens, the most basal plant possessing a gene encoding a BBE‐like protein, revealed its involvement in cellulose degradation by catalyzing the oxidation of cellobiose to the corresponding lactone. Thus, we hypothesize that BBE‐like proteins in plants were primarily employed in carbohydrate metabolism.