Fluorescent peptide sensors for tyrosylprotein sulfotransferase activity

An activity-based fluorescent sensor for the detection of the phenol sulfotransferase SULT1A1 in living cells

Human phenol sulfotransferases mediate the transfer of a sulfuryl moiety from the activated sulfate donor PAPS to hydroxy-containing substrates, altering substrate solubility and charge to affect phase II metabolism and cell signaling. Here, we present the development, computational modeling, in vitro enzymology, and biological application of STS-3, an activity-based fluorescent sensor for the SULT1A1 isoform.

Preparation of Tyrosylprotein Sulfotransferases for In Vitro One-Pot Enzymatic Synthesis of Sulfated Proteins/Peptides

Protein tyrosine sulfation (PTS), catalyzed by membrane-anchored tyrosylprotein sulfotransferase (TPST), is one of the most common post-translational modifications of secretory and transmembrane proteins. PTS, a key modulator of extracellular protein-protein interactions, accounts for various important biological activities, namely, virus entry, inflammation, coagulation, and sterility. The preparation and characterization of TPST is fundamental for understanding the synthesis of tyrosine-sulfated proteins and for studying PTS in biology. A sulfated protein was prepared using a TPST-coupled protein sulfation system that involves the generation of the active sulfate 3'-phosphoadenosine-5'-phosphosulfate (PAPS) through either PAPS synthetase (PAPSS) or phenol sulfotransferase. The preparation of sulfated proteins was confirmed through radiometric or immunochemical assays. In this study, enzymatically active Drosophila melanogaster TPST (DmTPST) and human TPSTs (hTPST1 and hTPST2) were expressed in Escherichia coli BL21(DE3) host cells and purified to homogeneity in high yield. Our results revealed that recombinant DmTPST was particularly useful considering its catalytic efficiency and ease of preparation in large quantities. This study provides tools for high-efficiency, one-step synthesis of sulfated proteins and peptides that are useful for further deciphering the mechanisms, functions, and future applications of PTS.

New tools for evaluating protein tyrosine sulfation: tyrosylprotein sulfotransferases (TPSTs) are novel targets for RAF protein kinase inhibitors

Protein tyrosine sulfation is a post-translational modification best known for regulating extracellular protein–protein interactions. Tyrosine sulfation is catalysed by two Golgi-resident enzymes termed tyrosylprotein sulfotransferases (TPSTs) 1 and 2, which transfer sulfate from the cofactor PAPS (3′-phosphoadenosine 5′-phosphosulfate) to a context-dependent tyrosine in a protein substrate. A lack of quantitative tyrosine sulfation assays has hampered the development of chemical biology approaches for the identification of small-molecule inhibitors of tyrosine sulfation. In the present paper, we describe the development of a non-radioactive mobility-based enzymatic assay for TPST1 and TPST2, through which the tyrosine sulfation of synthetic fluorescent peptides can be rapidly quantified. We exploit ligand binding and inhibitor screens to uncover a susceptibility of TPST1 and TPST2 to different classes of small molecules, including the anti-angiogenic compound suramin and the kinase inhibitor rottlerin. By screening the Published Kinase Inhibitor Set, we identified oxindole-based inhibitors of the Ser/Thr kinase RAF (rapidly accelerated fibrosarcoma) as low-micromolar inhibitors of TPST1 and TPST2. Interestingly, unrelated RAF inhibitors, exemplified by the dual BRAF/VEGFR2 inhibitor RAF265, were also TPST inhibitors in vitro. We propose that target-validated protein kinase inhibitors could be repurposed, or redesigned, as more-specific TPST inhibitors to help evaluate the sulfotyrosyl proteome. Finally, we speculate that mechanistic inhibition of cellular tyrosine sulfation might be relevant to some of the phenotypes observed in cells exposed to anionic TPST ligands and RAF protein kinase inhibitors.

Structural basis for the broad substrate specificity of the human tyrosylprotein sulfotransferase-1

Tyrosylprotein sulfotransferases (TPSTs) are enzymes that catalyze post-translational tyrosine sulfation of proteins. In humans, there are only two TPST isoforms, designated TPST1 and TPST2. In a previous study, we reported the crystal structure of TPST2, which revealed the catalytic mechanism of the tyrosine sulfation reaction. However, detailed molecular mechanisms underlying how TPSTs catalyse a variety of substrate proteins with different efficiencies and how TPSTs catalyze the sulfation of multiple tyrosine residues in a substrate protein remain unresolved. Here, we report two crystal structures of the human TPST1 complexed with two substrate peptides that are catalysed by human TPST1 with significantly different efficiencies. The distinct binding modes found in the two complexes provide insight into the sulfation mechanism for these substrates. The present study provides valuable information describing the molecular mechanism of post-translational protein modifications catalysed by TPSTs.

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.