In plant secondary metabolism, an alternative pathway of ester formation is facilitated by acyltransferases accepting 1-O-β-acetal esters (1-O-β-glucose esters) as acyl donors instead of coenzyme A thioesters. Molecular data indicate homology of these transferases with hydrolases of the serine carboxypeptidase type defining them as serine carboxypeptidase-like (SCPL) acyltransferases. During evolution, they apparently have been recruited from serine carboxypeptidases and adapted to take over acyl transfer function. SCPL acyltransferases belong to the highly divergent class of α/β hydrolases. These enzymes make use of a catalytic triad formed by a nucleophile, an acid and histidine acting as a charge relay system for the nucleophilic attack on amide or ester bonds. In analogy to SCPL acyltransferases, bacterial thioesterase domains are known which favour transferase activity over hydrolysis. Structure elucidation reveals water exclusion and a distortion of the oxyanion hole responsible for the changed activity. In plants, SCPL proteins form a large family. By sequence comparison, a distinguished number of Arabidopsis SCPL proteins cluster with proven SCPL acyltransferases. This indicates the occurrence of a large number of SCPL proteins co-opted to catalyse acyltransfer reactions. SCPL acyltransferases are ideal systems to investigate principles of functional adaptation and molecular evolution of plant genes.Serine carboxypeptidase-like (SCPL) acyltransferases are involved in the formation of esters, accepting 1-O-β-glucose esters as acyl donors. SCPL proteins make use of a catalytic triad formed by a nucleophile, an acid and histidine acting as a charge relay system for the nucleophilic attack on amide or ester bonds. During evolution, these enzymes apparently have been recruited from serine carboxypeptidases and adapted to take over acyl transfer instead of hydrolysis functions. By sequence comparison, a distinguished number of Arabidopsis SCPL proteins cluster with proven SCPL acyltransferases. These enzymes might be ideal systems to investigate principles of functional adaptation and molecular evolution of plant genes.

Members of the Brassicaceae family accumulate specific sinapate esters, i.e. sinapoylcholine (sinapine), which is considered as a major antinutritive compound in seeds of important crop plants like Brassica napus , and sinapoylmalate, which is implicated in UV‐B tolerance in leaves. We have studied the molecular regulation of the sinapate ester metabolism in B. napus , and we describe expression of genes, some properties of the encoded proteins and profiles of the metabolites and enzyme activities. The cloned cDNAs encoding the key enzymes of sinapine biosynthesis, UDP‐glucose (UDP‐Glc):B. napus sinapate glucosyltransferase (BnSGT1) and sinapoylglucose:B. napus choline sinapoyltransferase (BnSCT), were functionally expressed. BnSGT1 belongs to a subgroup of plant GTs catalysing the formation of 1‐O‐hydroxycinnamoyl‐β‐d ‐glucoses. BnSCT is another member of serine carboxypeptidase‐like (SCPL) family of acyltransferases. The B. napus genome contains at least two SGT and SCT genes, each derived from its progenitors B. oleracea and B. rapa . BnSGT1 and BnSCT activities are subjected to pronounced transcriptional regulation. BnSGT1 transcript level increases throughout early stages of seed development until the early cotyledonary stage, and stays constant in later stages. The highest level of BnSGT1 transcripts is reached in 2‐day‐old seedlings followed by a dramatic decrease. In contrast, expression of BnSCT is restricted to developing seeds. Regulation of gene expression at the transcript level seems to be responsible for changes of BnSGT1 and BnSCT activities during seed and seedling development of B. napus . Together with sinapine esterase (SCE) and sinapoylglucose:malate sinapoyltransferase (SMT), activities of BnSGT1 and BnSCT show a close correlation with the accumulation kinetics of the corresponding metabolites.

In plant secondary metabolism, an alternative pathway of ester formation is facilitated by acyltransferases accepting 1-O-β-acetal esters (1-O-β-glucose esters) as acyl donors instead of coenzyme A thioesters. Molecular data indicate homology of these transferases with hydrolases of the serine carboxypeptidase type defining them as serine carboxypeptidase-like (SCPL) acyltransferases. During evolution, they apparently have been recruited from serine carboxypeptidases and adapted to take over acyl transfer function. SCPL acyltransferases belong to the highly divergent class of α/β hydrolases. These enzymes make use of a catalytic triad formed by a nucleophile, an acid and histidine acting as a charge relay system for the nucleophilic attack on amide or ester bonds. In analogy to SCPL acyltransferases, bacterial thioesterase domains are known which favour transferase activity over hydrolysis. Structure elucidation reveals water exclusion and a distortion of the oxyanion hole responsible for the changed activity. In plants, SCPL proteins form a large family. By sequence comparison, a distinguished number of Arabidopsis SCPL proteins cluster with proven SCPL acyltransferases. This indicates the occurrence of a large number of SCPL proteins co-opted to catalyse acyltransfer reactions. SCPL acyltransferases are ideal systems to investigate principles of functional adaptation and molecular evolution of plant genes.Serine carboxypeptidase-like (SCPL) acyltransferases are involved in the formation of esters, accepting 1-O-β-glucose esters as acyl donors. SCPL proteins make use of a catalytic triad formed by a nucleophile, an acid and histidine acting as a charge relay system for the nucleophilic attack on amide or ester bonds. During evolution, these enzymes apparently have been recruited from serine carboxypeptidases and adapted to take over acyl transfer instead of hydrolysis functions. By sequence comparison, a distinguished number of Arabidopsis SCPL proteins cluster with proven SCPL acyltransferases. These enzymes might be ideal systems to investigate principles of functional adaptation and molecular evolution of plant genes.

Members of the Brassicaceae family accumulate specific sinapate esters, i.e. sinapoylcholine (sinapine), which is considered as a major antinutritive compound in seeds of important crop plants like Brassica napus , and sinapoylmalate, which is implicated in UV‐B tolerance in leaves. We have studied the molecular regulation of the sinapate ester metabolism in B. napus , and we describe expression of genes, some properties of the encoded proteins and profiles of the metabolites and enzyme activities. The cloned cDNAs encoding the key enzymes of sinapine biosynthesis, UDP‐glucose (UDP‐Glc):B. napus sinapate glucosyltransferase (BnSGT1) and sinapoylglucose:B. napus choline sinapoyltransferase (BnSCT), were functionally expressed. BnSGT1 belongs to a subgroup of plant GTs catalysing the formation of 1‐O‐hydroxycinnamoyl‐β‐d ‐glucoses. BnSCT is another member of serine carboxypeptidase‐like (SCPL) family of acyltransferases. The B. napus genome contains at least two SGT and SCT genes, each derived from its progenitors B. oleracea and B. rapa . BnSGT1 and BnSCT activities are subjected to pronounced transcriptional regulation. BnSGT1 transcript level increases throughout early stages of seed development until the early cotyledonary stage, and stays constant in later stages. The highest level of BnSGT1 transcripts is reached in 2‐day‐old seedlings followed by a dramatic decrease. In contrast, expression of BnSCT is restricted to developing seeds. Regulation of gene expression at the transcript level seems to be responsible for changes of BnSGT1 and BnSCT activities during seed and seedling development of B. napus . Together with sinapine esterase (SCE) and sinapoylglucose:malate sinapoyltransferase (SMT), activities of BnSGT1 and BnSCT show a close correlation with the accumulation kinetics of the corresponding metabolites.

In plant secondary metabolism, an alternative pathway of ester formation is facilitated by acyltransferases accepting 1-O-β-acetal esters (1-O-β-glucose esters) as acyl donors instead of coenzyme A thioesters. Molecular data indicate homology of these transferases with hydrolases of the serine carboxypeptidase type defining them as serine carboxypeptidase-like (SCPL) acyltransferases. During evolution, they apparently have been recruited from serine carboxypeptidases and adapted to take over acyl transfer function. SCPL acyltransferases belong to the highly divergent class of α/β hydrolases. These enzymes make use of a catalytic triad formed by a nucleophile, an acid and histidine acting as a charge relay system for the nucleophilic attack on amide or ester bonds. In analogy to SCPL acyltransferases, bacterial thioesterase domains are known which favour transferase activity over hydrolysis. Structure elucidation reveals water exclusion and a distortion of the oxyanion hole responsible for the changed activity. In plants, SCPL proteins form a large family. By sequence comparison, a distinguished number of Arabidopsis SCPL proteins cluster with proven SCPL acyltransferases. This indicates the occurrence of a large number of SCPL proteins co-opted to catalyse acyltransfer reactions. SCPL acyltransferases are ideal systems to investigate principles of functional adaptation and molecular evolution of plant genes.Serine carboxypeptidase-like (SCPL) acyltransferases are involved in the formation of esters, accepting 1-O-β-glucose esters as acyl donors. SCPL proteins make use of a catalytic triad formed by a nucleophile, an acid and histidine acting as a charge relay system for the nucleophilic attack on amide or ester bonds. During evolution, these enzymes apparently have been recruited from serine carboxypeptidases and adapted to take over acyl transfer instead of hydrolysis functions. By sequence comparison, a distinguished number of Arabidopsis SCPL proteins cluster with proven SCPL acyltransferases. These enzymes might be ideal systems to investigate principles of functional adaptation and molecular evolution of plant genes.

Members of the Brassicaceae family accumulate specific sinapate esters, i.e. sinapoylcholine (sinapine), which is considered as a major antinutritive compound in seeds of important crop plants like Brassica napus , and sinapoylmalate, which is implicated in UV‐B tolerance in leaves. We have studied the molecular regulation of the sinapate ester metabolism in B. napus , and we describe expression of genes, some properties of the encoded proteins and profiles of the metabolites and enzyme activities. The cloned cDNAs encoding the key enzymes of sinapine biosynthesis, UDP‐glucose (UDP‐Glc):B. napus sinapate glucosyltransferase (BnSGT1) and sinapoylglucose:B. napus choline sinapoyltransferase (BnSCT), were functionally expressed. BnSGT1 belongs to a subgroup of plant GTs catalysing the formation of 1‐O‐hydroxycinnamoyl‐β‐d ‐glucoses. BnSCT is another member of serine carboxypeptidase‐like (SCPL) family of acyltransferases. The B. napus genome contains at least two SGT and SCT genes, each derived from its progenitors B. oleracea and B. rapa . BnSGT1 and BnSCT activities are subjected to pronounced transcriptional regulation. BnSGT1 transcript level increases throughout early stages of seed development until the early cotyledonary stage, and stays constant in later stages. The highest level of BnSGT1 transcripts is reached in 2‐day‐old seedlings followed by a dramatic decrease. In contrast, expression of BnSCT is restricted to developing seeds. Regulation of gene expression at the transcript level seems to be responsible for changes of BnSGT1 and BnSCT activities during seed and seedling development of B. napus . Together with sinapine esterase (SCE) and sinapoylglucose:malate sinapoyltransferase (SMT), activities of BnSGT1 and BnSCT show a close correlation with the accumulation kinetics of the corresponding metabolites.