Biochemistry and molecular biology of plant sulfotransferases

Abstract

It is now well established that, in mammals, sulfate conjugation constitutes an important reaction in the transformation of xenobiotics and in the modulation of the biological activity of steroid hormones and neurotransmitter. The presence of a sulfate group on some molecules can also be a prerequisite for their biological function. For example, it is well known that the sulfate groups are directly involved in the molecular interaction between heparin and antithrombin III. In plants, sulfation also seems to play an important role in the intermolecular recognition and signaling processes, as indicated by the requirement of a sulfate moiety for the biological activity of gallic acid glucoside sulfate in the seismonastic and gravitropic movements of plants, and of Nod RM1 in the cortical cell division during early nodule initiation in Rhizobium meliloti-alfalfa interaction. In addition, recent studies indicate that flavonoid conjugates, including the sulfate esters, may play a role in the regulation of plant growth by strongly binding the naphthylphthalamic acid receptor, thus blocking the quercetin-stimulated accumulation of the auxin phytohormone. Although several sulfated metabolites are known to accumulate in a variety of plant species, the study of enzymes that catalyze the sulfation reaction in plants lagged considerably compared to those conducted with their mammalian homologs. This apparent lack of interest may have been because the function of plant-sulfated metabolites is difficult to predict, since their accumulation is often restricted to a limited number of species. Despite this limitation, several plant sulfotransferases (STs) have been characterized at the biochemical level, and the cDNA clones encoding six plant STs have been isolated. Based on sequence homology, the plant ST coding sequences are grouped under the SULT3 family, also known as the flavonol ST family. This review summarizes our current knowledge of the plant STs and focuses on the functional significance of the sulfate conjugation in plant growth, development, and adaptation to stress.

Identification of a novel flavonoid glycoside sulfotransferase in Arabidopsis thaliana

“…The K m values for PAPS, determined with fixed concentration of kaempferol-3-glucoside, was 0.4 mM. which is within the range of K m values (0.2 0.4 mM) previously reported for other flavonoid sulfotransferases (21).…”

“…4). Previous studies have shown that flavonol sulfotransferases derived from Flaveria species displayed optimum pH ranging 6.0 8.5 (21). Considering that the vacuolar pH of plant cells is about 5.0 5.5 (22) and that the flavonol glycosides accumulates mainly in the vacuole (23), it is possible that AtSULT202B7 might somehow be transported into this acidic organelle and sulfate the flavonol glycosides locally as substrates.…”

Differential Subcellular Localization and Expression of ATP Sulfurylase and 5′-Adenylylsulfate Reductase during Ontogenesis of Arabidopsis Leaves Indicates That Cytosolic and Plastid Forms of ATP Sulfurylase May Have Specialized Functions

“…Plastids contain all the enzymes necessary for reductive assimilation of sulfate (Schiff, 1983;Schmidt, 1986). However, all known sulfotransferases that carry out sulfate esterification are cytosolic enzymes (Varin et al, 1997), indicating the need for activated sulfate in the cytosol. A cytosolic isoenzyme of ATP sulfurylase has been reported in some plant species (Lunn et al, 1990;Renosto et al, 1993).…”

“…Sulfur is assimilated in either the oxidized or the reduced form (Leustek and Saito, 1999). When incorporated in the oxidized form it is used for esterification of a variety of compounds including polysaccharides such as carrageenans and agaroids (McCandless and Craigie, 1979), sulfated flavonoids (Varin et al, 1997), glucosinolates, and many others . Alternatively, sulfate is reduced to sulfide and is then incorporated as the thiol group of Cys.…”

“…APS can be further phosphorylated by APS kinase (EC 2.7.1.25), forming 3Ј-phospho-5Ј-adenylylsulfate (PAPS). PAPS is the sulfuryl donor for esterification of metabolites catalyzed by sulfotransferases (Varin et al, 1997). In contrast, APS is used directly as the substrate for the reduction pathway.…”