Sulfotransferases from Plants, Algae and Phototrophic Bacteria

Abstract

Sulfotransferases (SULTs) catalyze the transfer of a sulfuryl group (SO3) from the universal donor 3'-phosphoadenosine 5'-phosphosulfate to a hydroxyl group of various substrates in a process called the sulfonation reaction. These enzymes share highly conserved sequence regions across all kingdoms; however, their substrates and physiological function are predicted to be very diverse. In mammals, the sulfonation reaction is involved in mechanisms of cellular detoxification and in the modulation of the biological activity of steroid hormones and neurotransmitters. In plants, few SULTs have been characterized despite the large number of sequences found in databases. Understanding of their role in plant biology is still relatively speculative. Since the cloning of the first plant SULT cDNA more than 10 years ago from Flaveria chloraefolia, functional genomic approaches, particularly in Arabidopsis thaliana, have led to the characterization of brassinosteroid, hydroxyjasmonate, desulfoglucosinolate and flavonoid SULTs. However, these efforts are hindered by a limited knowledge of plant sulfated metabolites. A detailed analysis of plant SULT sequences revealed that at present, phylogeny is of limited value to predict biochemical function. For instance, A. thaliana desulfoglucosinolate SULTs form a clade with the Flaveria flavonol SULTs. Ten of the 17 A. thaliana SULTs belong to a single homogeneous clade, suggesting that most of the divergence occurred after the diversification of this plant lineage. We present here a detailed overview of the molecular phylogeny, characterization, and biological roles of SULTs in plants. We also describe the current state of knowledge of sulfonation in algae, as well as in phototrophic bacteria, where the SULT domain can be present in multidomain proteins.