Activities of Arabidopsis sinapoylglucose:malate sinapoyltransferase shed light on functional diversification of serine carboxypeptidase-like acyltransferases

Analysis of the catalytic properties of Arabidopsis SMT revealed besides synthesis of sinapoyl-l-malate, minor hydrolytic and disproportionation activities to produce free sinapic acid and 1,2-di-O-sinapoyl-β-glucose, respectively. The SMT homology structure model 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. We discuss that the SMT gene emerged from recent gene duplication events and might be, with four other tandemly arranged SCPL acyltransferase genes, still on functional development.