Unser 10. Leibniz Plant Biochemistry Symposium am 7. und 8. Mai war ein großer Erfolg. Thematisch ging es in diesem Jahr um neue Methoden und Forschungsansätze der Naturstoffchemie. Die exzellenten Vorträge über Wirkstoffe…
Omanische Heilpflanze im Fokus der Phytochemie IPB-Wissenschaftler und Partner aus Dhofar haben jüngst die omanische Heilpflanze Terminalia dhofarica unter die phytochemische Lupe genommen. Die Pflanze ist reich an…
Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
Stehle, F.; Brandt, W.; Stubbs, M. T.; Milkowski, C.; Strack, D.;Sinapoyltransferases in the light of molecular evolutionPhytochemistry701652-1662(2009)DOI: 10.1016/j.phytochem.2009.07.023
Acylation is a prevalent chemical modification that to a significant extent accounts for the tremendous diversity of plant metabolites. To catalyze acyl transfer reactions, higher plants have evolved acyltransferases that accept β-acetal esters, typically 1-O-glucose esters, as an alternative to the ubiquitously occurring CoA-thioester-dependent enzymes. Shared homology indicates that the β-acetal ester-dependent acyltransferases are derived from a common hydrolytic ancestor of the Serine CarboxyPeptidase (SCP) type, giving rise to the name Serine CarboxyPeptidase-Like (SCPL) acyltransferases. We have analyzed structure–function relationships, reaction mechanism and sequence evolution of Arabidopsis 1-O-sinapoyl-β-glucose:l-malate sinapoyltransferase (AtSMT) and related enzymes to investigate molecular changes required to impart acyltransferase activity to hydrolytic enzymes. AtSMT has maintained the catalytic triad of the hydrolytic ancestor as well as part of the H-bond network for substrate recognition to bind the acyl acceptor l-malate. A Glu/Asp substitution at the amino acid position preceding the catalytic Ser supports binding of the acyl donor 1-O-sinapoyl-β-glucose and was found highly conserved among SCPL acyltransferases. The AtSMT-catalyzed acyl transfer reaction follows a random sequential bi-bi mechanism that requires both substrates 1-O-sinapoyl-β-glucose and l-malate bound in an enzyme donor–acceptor complex to initiate acyl transfer. Together with the strong fixation of the acyl acceptor l-malate, the acquisition of this reaction mechanism favours transacylation over hydrolysis in AtSMT catalysis. The model structure and enzymatic side activities reveal that the AtSMT-mediated acyl transfer proceeds via a short-lived acyl enzyme complex. With regard to evolution, the SCPL acyltransferase clade most likely represents a recent development. The encoding genes are organized in a tandem-arranged cluster with partly overlapping functions. With other enzymes encoded by the respective gene cluster on Arabidopsis chromosome 2, AtSMT shares the enzymatic side activity to disproportionate 1-O-sinapoyl-β-glucoses to produce 1,2-di-O-sinapoyl-β-glucose. In the absence of the acyl acceptor l-malate, a residual esterase activity became obvious as a remnant of the hydrolytic ancestor. With regard to the evolution of Arabidopsis SCPL acyltransferases, our results suggest early neofunctionalization of the hydrolytic ancestor toward acyltransferase activity and acyl donor specificity for 1-O-sinapoyl-β-glucose followed by subfunctionalization to recognize different acyl acceptors.
Publikation
Stehle, F.; Brandt, W.; Schmidt, J.; Milkowski, C.; Strack, D.;Activities of Arabidopsis sinapoylglucose:malate sinapoyltransferase shed light on functional diversification of serine carboxypeptidase-like acyltransferasesPhytochemistry691826-1831(2008)DOI: 10.1016/j.phytochem.2008.03.021
Analysis of the catalytic properties of the serine carboxypeptidase-like (SCPL) 1-O-sinapoyl-β-glucose:l-malate sinapoyltransferase (SMT) from Arabidopsis showed that the enzyme exhibits besides its primary sinapoylation of l-malate, minor hydrolytic and disproportionation activities, producing free sinapic acid and 1,2-di-O-sinapoyl-β-glucose, respectively. The ability of the enzyme to liberate sinapic acid from the donor molecule 1-O-sinapoyl-β-glucose indicates the existence of a short-lived acylenzyme intermediate in the proposed random sequential bi–bi mechanism of catalysis. SMT-catalyzed formation of disinapoylglucose has been corroborated by docking studies with an established homology structure model that illustrates the possible binding of two 1-O-sinapoyl-β-glucose molecules in the active site and the intermolecular reaction of the two glucose esters. The SMT gene is embedded in a tandem cluster of five SCPL sinapoyltransferase genes, which encode enzymes with high amino acid sequence identities and partially overlapping substrate specificities. We assume that in recent duplications of genes encoding SCPL proteins, neofunctionalization of the duplicates to accept 1-O-sinapoyl-β-glucose as acyl donor was gained first, followed by subfunctionalization leading to different acyl acceptor specificities.