Tyrosylprotein sulfotransferase in rat submandibular salivary glands

Tyrosine sulfation as a protein post-translational modification

Integration of inorganic sulfate into biological molecules plays an important role in biological systems and is directly involved in the instigation of diseases. Protein tyrosine sulfation (PTS) is a common post-translational modification that was first reported in the literature fifty years ago. However, the significance of PTS under physiological conditions and its link to diseases have just begun to be appreciated in recent years. PTS is catalyzed by tyrosylprotein sulfotransferase (TPST) through transfer of an activated sulfate from 3'-phosphoadenosine-5'-phosphosulfate to tyrosine in a variety of proteins and peptides. Currently, only a small fraction of sulfated proteins is known and the understanding of the biological sulfation mechanisms is still in progress. In this review, we give an introductory and selective brief review of PTS and then summarize the basic biochemical information including the activity and the preparation of TPST, methods for the determination of PTS, and kinetics and reaction mechanism of TPST. This information is fundamental for the further exploration of the function of PTS that induces protein-protein interactions and the subsequent biochemical and physiological reactions.

Mass spectrometric kinetic analysis of human tyrosylprotein sulfotransferase-1 and -2

Protein tyrosine O-sulfation, a widespread post-translational modification, is mediated by two Golgi enzymes, tyrosylprotein sulfotransferase-1 and -2. These enzymes catalyze the transfer of sulfate from the universal sulfate donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to the hydroxyl group of tyrosine residues to form tyrosine O-sulfate ester and PAP. More than 60 proteins have been identified to be tyrosine sulfated including several G protein-coupled receptors, such as CC-chemokine receptor 8 (CCR8) that is implicated in allergic inflammation, asthma, and atherogenesis. However, the kinetic properties of purified tyrosylprotein sulfotransferase (TPST)-1 and -2 have not been previously reported. Moreover, currently there is no available quantitative TPST assay that can directly monitor individual sulfation of a series of tyrosine residues, which is present in most known substrates. We chose an MS-approach to address this limitation. In this study, a liquid chromatography electrospray ionisation mass spectrometry (LC/ESI-MS)-based TPST assay was developed to determine the kinetic parameters of individual TPSTs and a mixture of both isozymes using CCR8 peptides as substrates that have three tyrosine residues in series. Our method can differentiate between mono- and disulfated products, and our results show that the K(m,app) for the monosulfated substrate was 5-fold less than the nonsulfated substrate. The development of this method is the initial step in the investigation of kinetic parameters of the sequential tyrosine sulfation of chemokine receptors by TPSTs and in determining its catalytic mechanism.

Tyrosine sulfation of statherin

Tyrosylprotein sulfotransferase (TPST), responsible for the sulfation of a variety of secretory and membrane proteins, has been identified and characterized in submandibular salivary glands (William et al. Arch Biochem Biophys 1997; 338: 90-96). In the present study we demonstrate the sulfation of a salivary secretory protein, statherin, by the tyrosylprotein sulfotransferase present in human saliva. Optimum statherin sulfation was observed at pH 6.5 and at 20 mm MnCl₂. Increase in the level of total sulfation was observed with increasing statherin concentration. The K_mvalue of tyrosylprotein sulfotransferase for statherin was 40 μM. Analysis of the sulfated statherin product on SDS-polyacrylamide gel electrophoresis followed by autoradiography revealed ³⁵S-labelling of a 5 kDa statherin. Further analysis of the sulfated statherin revealed the sulfation on tyrosyl residue. This study is the first report demonstrating tyrosine sulfation of a salivary secretory protein. The implications of this sulfation of statherin in hydroxyapatite binding and Actinomyces viscosus interactions are discussed.

Differential enzymatic characteristics and tissue-specific expression of human TPST-1 and TPST-2

Protein tyrosine sulfation is emerging as a widespread post-translational modification in multicellular eukaryotes. The responsible enzyme, named tyrosylprotein sulfotransferase (TPST), catalyzes the sulfate transfer from 3'-phosphoadenosine 5'-phosphosulfate to tyrosine residues of proteins. Two distinct TPSTs, designated TPST-1 and TPST-2, had previously been identified. In the present study, we cloned human TPST-1 and TPST-2 expressed and characterized the recombinant enzymes using peptide substrates. These enzymes displayed distinct acidic pH optima and stimulatory effects of Mn(2+). Additionally, the activity of TPST-2, but not TPST-1, was stimulated in the presence of Mg(2+). Compared with TPST-2, TPST-1 displayed considerably lower K(m) and V(max) for the majority of the tested peptide substrates, implying their differential substrate specificity. Quantitative real-time PCR analysis showed that although the two TPSTs were co-expressed in all 20 human tissues examined, the levels of expression of TPST-1 and TPST-2 varied significantly among different tissues. These latter findings may imply distinct physiological functions of TPST-1 and TPST-2.

Identification and characterization of tyrosylprotein sulfotransferase from human saliva

Tyrosylprotein sulfotransferase (TPST), the enzyme responsible for the sulfation of tyrosine residues, has been identified and characterized in submandibular salivary glands previously (William et al. Arch Biochem Biophys 338: 90-96). Tyrosylprotein sulfotransferase catalyses the sulfation of a variety of secretory and membrane proteins and is believed to be present only in the cell. In the present study, this enzyme was identified for the first time in human saliva. Analysis of human saliva and parotid saliva for the presence of tyrosylprotein sulfotransferase revealed tyrosine sulfating activity displayed by both whole saliva and parotid saliva at pH optimum of 6.8. In contrast to tyrosylprotein sulfotransferase isolated from submandibular salivary glands, salivary enzyme does not require the presence of Triton X-100, NaF and 5'AMP for maximal activity. Similar to the submandibular TPST, the enzyme from saliva also required MnCl₂ for its activity. Maximum TPST activity was observed at 20mM MnCl₂. The enzyme from saliva was immunoprecipitated and purified by immunoaffinity column using anti-TPST antibody. Affinity purified salivary TPST showed a single band of 50-54 kDa. This study is the first report characterizing a tyrosylprotein sulfotransferase in a secretory fluid.

Zebrafish tyrosylprotein sulfotransferase: molecular cloning, expression, and functional characterization

By employing the reverse transcriptase-polymerase chain reaction technique in conjunction with 3' rapid amplification of cDNA ends, a full-length cDNA encoding a zebrafish (Danio rerio) tyrosylprotein sulfotransferase (TPST) was cloned and sequenced. Sequence analysis revealed that this zebrafish TPST is, at the amino acid sequence level, 66% and 60% identical to the human and mouse TPST-1 and TPST-2, respectively. The recombinant form of the zebrafish TPST, expressed in COS-7 cells, exhibited a pH optimum at 5.75. Manganese appeared to exert a stimulatory effect on the zebrafish TPST. The activity of the enzyme determined in the presence of 20 mM MnCl2 was more than 2.5 times that determined in the absence of MnCl2. Of the other nine divalent metal cations tested at a 10 mM concentration, Co2+ also showed a considerable stimulatory effect, while Ca2+, Pb2+, and Cd2+ exerted some inhibitory effects. The other four divalent cations, Fe2+, Cu2+, Zn2+, and Hg2+, inhibited completely the sulfating activity of the zebrafish TPST. Using the wild-type and mutated P-selectin glycoprotein ligand-1 N-terminal peptides as substrates, the zebrafish TPST was shown to exhibit a high degree of substrate specificity for the tyrosine residue on the C-terminal side of the peptide. These results constitute a first study on the cloning, expression, and characterization of a zebrafish cytosolic TPST.

Isolation of tyrosylprotein sulfotransferase from rat liver

1. Tyrosylprotein sulfotransferase (TPST) is involved in the posttranslational modification of proteins and plays a critical role in the biological activity and secretion of proteins. A simple method has been developed to isolate the TPST (28% yield) from rat liver, using polyclonal anti-TPST antibodies. 2. The protein fractions eluted from antibody affinity column showed TPST activity and revealed a 50-54 kDa protein band in the silver stained SDS-polyacrylamide gels. 3. The enzyme exhibited optimum activity at pH 5.5 with 20 mM MnCl2. Unlike the TPST activity of the Golgi membrane, the activity of the purified enzyme was not stimulated by NaF, 5'-AMP, and Triton X-100. 4. The antibody was also used to study the TPST protein turnover in rat liver of animals that were given [35S]methionine. The TPST protein synthesis assessed by measuring initial rates of incorporation of [35S]methionine into TPST protein showed enzyme synthesis for up to 60 min. 35S-labeled TPST protein of rat liver was degraded with a half-life of 30 hr. 5. The immunoaffinity purification method using rat liver as an enzyme source appeared to be very simple, rapid, and easy to perform with significant enzyme recovery. Further, the antibody was also found to be useful in the study involving TPST protein metabolism.

Effect of lipids on glycoprotein sulphotransferase activity in rat submandibular salivary glands

Although glycoprotein sulphation has been implicated in the processing of salivary mucin, little is known about the regulation of the enzyme responsible for this event. Using desulphated glycoprotein as sulphate acceptor, the glycoprotein sulphotransferase (GPST) from Golgi membranes of submandibular salivary gland was used to study the effect of various lipids on its activity. The GPST activity in the Golgi membrane was 0.7 pmol/mg protein per min and the activity was extractable by Triton S-100. The Km of the solubilized GPST for glycoprotein and 3'-phosphoadenosine 5'-phosphosulphate (PAPS) were 11 and 0.2 microM, respectively. Among the various lipids tested, phosphatidylinositol and sphingosine stimulated the GPST activity, while other lipids such as sphingomyelin, phosphatidylcholine and phosphatidylserine did not produce a significant effect. At 12 mol% (when expressed as mol% of sphingosine to total phospholipids plus Triton X-100) of sphingosine concentration, the enzyme activity was increased nearly 1.7-fold. The stimulatory effect of sphingosine was accompanied by a significant decrease in Km for glycoprotein from 11 to 2 microM but the increase in Vmax was small. In contrast, the sphingosine effect did not change the Km for PAPS but increased the Vmax nearly two fold. Of the two sphingosine analogues tested, threosphinganine and erythrosphinganine had a lesser stimulatory effect than sphingosine. Stearylamine was partially active, whereas the amino acids (glutamate, aspartate, glutamine, asparagine and serine) were not. These observations and our earlier finding of tyrosylprotein sulphotransferase inhibition by sphingosine demonstrate diverse sphingosine effects on the post-translational sulphation involved in the processing of salivary proteins and suggest an important role for sphingosine in the regulation of salivary protein sulphation.

Effect of prostaglandins on tyrosylprotein sulfotransferase activity in rat submandibular salivary glands

1. Tyrosylprotein sulfotransferase (TPST) is a key enzyme in the processing of several secretory proteins, including those found in saliva. In this report, the effect of prostaglandins (PG) on TPST activity in submandibular salivary gland was investigated. 2. The results revealed that PGE2 exhibited TPST stimulatory activity with a 1.5-fold stimulation at 100 microM concentration and a half maximal stimulation at 50 microM. The PGE2 stimulation was accompanied by an increase in the affinity of TPST towards sulfate acceptor (Km 1.4 microM-->0.12 microM) with little change in Vmax. 3. The TPST activity was also stimulated by two other major prostaglandins of salivary glands, PGF2 alpha and 6-Keto-PGF 1 alpha, however to lesser extent, 22 and 23%, respectively. Arachidonic acid, an intermediate prostaglandin precursor, had no effect on TPST activity. 4. The results suggest that prostaglandins and in particular PGE2 may play a role in the regulation of TPST catalyzed secretory protein tyrosine sulfation in salivary glands.

Effect of sofalcone on tyrosylprotein sulfotransferase

1. Gastric mucus glycoproteins are actively involved in the maintenance of mucosal integrity and the impairment in their elaboration is often a prominent feature in gastric pathology. In this study, we investigated the effect of an antiulcer drug, sofalcone, on the activity of tyrosylprotein sulfotransferase enzyme involved in the secretion of proteins and glycoproteins in male 8 week old rats. 2. Using poly-Glu6, Ala3, Tyr1 (EAY) as sulfate acceptor, and 3'phosphoadenosine 5'-phosphosulfate (PAPS) as sulfate donor the optimum Golgi TPST activity was obtained at pH 6.8, in presence of 0.5% Triton X-100, 20 mM MnCl2, 50 mM NaF and 2 mM 5'-AMP. 3. Introduction of sofalcone to the reaction mixture led to the enhancement in TPST activity. The rate of stimulation was proportional to the drug concentration up to 30 micrograms, at which concentration, a 55% increase in TPST activity was attained. 4. The results attest further to the value of sofalcone as a potent mucosal strengthening agent, and suggest that the agent may promote mucin secretion via activation of tyrosine sulfation.

Protein tyrosine sulfation, 1993--an update

Sulfation is the most abundant post-translational modification of tyrosine residues and occurs in many soluble and membrane proteins passing through the secretory pathway of metazoan cells. The sulfation reaction is catalysed by tyrosylprotein sulfotransferase, a membrane-bound enzyme of the trans-Golgi-network. Tyrosylprotein sulfotransferase has been purified and its substrate specificity characterized. Tyrosine sulfation has been shown to be important for protein-protein interactions occurring during the intracellular transport of proteins and upon their secretion.