The post-translational sulfation of tyrosine residues occurs in numerous secreted and integral membrane proteins and, in many cases, plays a crucial role in controlling the interactions of these proteins with physiological binding partners as well as invading pathogens. Recent advances in our understanding of protein tyrosine sulfation have come about owing to the cloning of two human tyrosylprotein sulfotransferases (TPST-1 and TPST-2), the development of novel analytical and synthetic methodologies and detailed studies of proteins and peptides containing sulfotyrosine residues. In this article, we describe the TPST enzymes, review the major techniques available for studying the presence, location and function of tyrosine sulfation in proteins and discuss the biological functions and biochemical interactions of several proteins (or protein families) in which tyrosine sulfation influences the protein function. In particular, we describe the detailed evidence supporting the importance of tyrosine sulfation in the cellular adhesion function of P-selectin glycoprotein ligand-1, the leukocyte trafficking and pathogen invasion functions of chemokine receptors and the ligand binding and activation of other G-protein-coupled receptors by complement proteins, phospholipdis and glycoprotein hormones.

Summary Sulfation of tyrosine is a common posttranslational modification of secreted proteins that influences numerous physiological and pathological processes. Studies of tyrosine sulfation have been hindered by the difficulty of introducing sulfate groups at specific positions of peptides and proteins. Here we report a general strategy for synthesis of peptides containing sulfotyrosine at one or more specific position(s). The approach provides a substantial improvement in both yield and convenience over existing methods. Using synthetic sulfopeptides derived from the chemokine receptor CCR3, we demonstrate that sulfation enhances affinity for the chemokine eotaxin by ∼7-fold or more than 28-fold, depending on which of two adjacent tyrosine residues is sulfated. The new synthetic methodology will substantially enhance efforts to understand the functional and structural consequences of protein tyrosine sulfation.

The interactions of chemokines with their G protein-coupled receptors play critical roles in the control of leukocyte trafficking in normal homeostasis and in inflammatory responses. Tyrosine sulfation is a common post-translational modification in the amino-terminal regions of chemokine receptors. However, tyrosine sulfation of chemokine receptors is commonly incomplete or heterogeneous. To investigate the possibility that differential sulfation of two adjacent tyrosine residues could bias the responses of chemokine receptor CCR3 to different chemokines, we have studied the binding of three chemokines (eotaxin-1/CCL11, eotaxin-2/CCL24, and eotaxin-3/CCL26) to an N-terminal CCR3-derived peptide in each of its four possible sulfation states. Whereas the nonsulfated peptide binds to the three chemokines with approximately equal affinity, sulfation of Tyr-16 gives rise to 9-16-fold selectivity for eotaxin-1 over the other two chemokines. Subsequent sulfation of Tyr-17 contributes additively to the affinity for eotaxin-1 and eotaxin-2 but cooperatively to the affinity for eotaxin-3. The doubly sulfated peptide selectively binds to both eotaxin-1 and eotaxin-3 approximately 10-fold more tightly than to eotaxin-2. Nuclear magnetic resonance chemical shift mapping indicates that these variations in affinity probably result from only subtle differences in the chemokine surfaces interacting with these receptor peptides. These data support the proposal that variations in sulfation states or levels may regulate the responsiveness of chemokine receptors to their cognate chemokines.

Most common genetic factors known to cause intellectual disability are Down syndrome and Fragile X syndrome. However, the underlying cellular and molecular mechanisms of intellectual disability remain unclear. Recently, dendritic spine dysmorphogenesis and impaired local protein synthesis are posited to contribute to the cellular mechanisms of intellectual disability. Here, we show that Down syndrome critical region1 (DSCR1) interacts with Fragile X mental retardation protein (FMRP) and regulates both dendritic spine morphogenesis and local protein synthesis. Interestingly, decreasing the level of FMRP restores the DSCR1-induced changes in dendritic spine morphology. Our results imply that DSCR1 is a novel regulator of FMRP and that Fragile X syndrome and Down syndrome may share disturbances in common pathways that regulate dendritic spine morphology and local protein synthesis.

GSK1322322 is a potent inhibitor of peptide deformylase, an essential bacterial enzyme required for protein maturation. GSK1322322 is active against community-acquired skin and respiratory tract pathogens, including methicillin-resistant Staphylococcus aureus, multidrug-resistant Streptococcus pneumoniae, and atypical pathogens. This phase I, randomized, doubleblind, placebo-controlled, 2-part, single-dose, dose escalation study (first time in humans) evaluated the safety, tolerability, and pharmacokinetics of GSK1322322 (powder-in-bottle formulation) in healthy volunteers. In part A, dose escalation included GSK1322322 doses of 100, 200, 400, 800, and 1,500 mg under fasting conditions and 800 mg administered with a high-fat meal. In part B, higher doses of GSK1322322 (2,000, 3,000, and 4,000 mg) were evaluated under fasting conditions. Of the 39 volunteers enrolled in the study, 29 and 10 volunteers were treated with GSK1322322 and placebo, respectively. Upon single-dose administration, GSK1322322 was absorbed rapidly, with median times to maximum plasma concentration (T max ) ranging from 0.5 to 1.0 h. The maximum observed plasma concentration (C max ) and exposure (area under the concentration-time curve [AUC]) of GSK1322322 were greater than dose proportional between 100 and 1,500 mg and less than dose proportional between 1,500 and 4,000 mg. Administration of the drug with a high-fat meal reduced the rate of absorption (reduced C max and delayed T max ) without affecting the extent of absorption (no effect on AUC). GSK1322322 was generally well tolerated, with all adverse events being mild to moderate in intensity during both parts of the study. The most frequently reported adverse event was headache. Data from this study support further evaluation of GSK1322322.