Tyrosine sulfation of yolk proteins 1, 2, and 3 in Drosophila melanogaster

Custom Workflow for the Confident Identification of Sulfotyrosine-Containing Peptides and Their Discrimination from Phosphopeptides

Protein tyrosine sulfation (sY) is a post-translational modification (PTM) catalyzed by Golgi-resident tyrosyl protein sulfo transferases (TPSTs). Information on sY in humans is currently limited to ∼50 proteins, with only a handful having verified sites of sulfation. As such, the contribution of sulfation to the regulation of biological processes remains poorly defined. Mass spectrometry (MS)-based proteomics is the method of choice for PTM analysis but has yet to be applied for systematic investigation of the "sulfome", primarily due to issues associated with discrimination of sY-containing from phosphotyrosine (pY)-containing peptides. In this study, we developed an MS-based workflow for sY-peptide characterization, incorporating optimized Zr4+ immobilized metal-ion affinity chromatography (IMAC) and TiO2 enrichment strategies. Extensive characterization of a panel of sY- and pY-peptides using an array of fragmentation regimes (CID, HCD, EThcD, ETciD, UVPD) highlighted differences in the generation of site-determining product ions and allowed us to develop a strategy for differentiating sulfated peptides from nominally isobaric phosphopeptides based on low collision energy-induced neutral loss. Application of our "sulfomics" workflow to a HEK-293 cell extracellular secretome facilitated identification of 21 new sulfotyrosine-containing proteins, several of which we validate enzymatically, and reveals new interplay between enzymes relevant to both protein and glycan sulfation.

Sulfoconjugation of protein peptides and glycoproteins in physiology and diseases

Protein sulfoconjugation, or sulfation, represents a critical post-translational modification (PTM) process that involves the attachment of sulfate groups to various positions of substrates within the protein peptides or glycoproteins. This process plays a dynamic and complex role in many physiological and pathological processes. Here, we summarize the importance of sulfation in the fields of oncology, virology, drug-induced liver injury (DILI), inflammatory bowel disease (IBD), and atherosclerosis. In oncology, sulfation is involved in tumor initiation, progression, and migration. In virology, sulfation influences viral entry, replication, and host immune response. In DILI, sulfation is associated with the incidence of DILI, where altered sulfation affects drug metabolism and toxicity. In IBD, dysregulation of sulfation compromises mucosal barrier and immune response. In atherosclerosis, sulfation influences the development of atherosclerosis by modulating the accumulation of lipoprotein, and the inflammation, proliferation, and migration of smooth muscle cells. The current review underscores the importance of further research to unravel the underlying mechanisms and therapeutic potential of targeting sulfoconjugation in various diseases. A better understanding of sulfation could facilitate the emergence of innovative diagnostic or therapeutic strategies.

Considerations for defining +80 Da mass shifts in mass spectrometry-based proteomics: phosphorylation and beyond

Post-translational modifications (PTMs) are ubiquitous and key to regulating protein function. Understanding the dynamics of individual PTMs and their biological roles requires robust characterisation. Mass spectrometry (MS) is the method of choice for the identification and quantification of protein modifications. This article focusses on the MS-based analysis of those covalent modifications that induce a mass shift of +80 Da, notably phosphorylation and sulfation, given the challenges associated with their discrimination and pinpointing the sites of modification on a polypeptide chain. Phosphorylation in particular is highly abundant, dynamic and can occur on numerous residues to invoke specific functions, hence robust characterisation is crucial to understanding biological relevance. Showcasing our work in the context of other developments in the field, we highlight approaches for enrichment and site localisation of phosphorylated (canonical and non-canonical) and sulfated peptides, as well as modification analysis in the context of intact proteins (top down proteomics) to explore combinatorial roles. Finally, we discuss the application of native ion-mobility MS to explore the effect of these PTMs on protein structure and ligand binding.

Fluorosulfate as a Latent Sulfate in Peptides and Proteins

Sulfation widely exists in the eukaryotic proteome. However, understanding the biological functions of sulfation in peptides and proteins has been hampered by the lack of methods to control its spatial or temporal distribution in the proteome. Herein, we report that fluorosulfate can serve as a latent precursor of sulfate in peptides and proteins, which can be efficiently converted to sulfate by hydroxamic acid reagents under physiologically relevant conditions. Photocaging the hydroxamic acid reagents further allowed for the light-controlled activation of functional sulfopeptides. This work provides a valuable tool for probing the functional roles of sulfation in peptides and proteins.

Inhibition of the SLC35B2-TPST2 Axis of Tyrosine Sulfation Attenuates the Growth and Metastasis of Pancreatic Ductal Adenocarcinom

BACKGROUND & AIMS

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer deaths in the United States. Tyrosine sulfation, catalyzed by the tyrosylprotein sulfotransferase 2 (TPST2), is a post-translational modification essential for protein-protein interactions and cellular functions. Solute carrier family 35 member B (SLC35B2) is a key transporter that transports the universal sulfate donor 3'-phosphoadenosine 5'-phosphosulfate into the Golgi apparatus where the protein sulfation occurs. The goal of this study was to determine whether and how the SLC35B2-TPST2 axis of tyrosine sulfation plays a role in PDAC.

METHODS

Gene expression was analyzed in PDAC patients and mice. Human PDAC MIA PaCa-2 and PANC-1 cells were used for in vitro studies. TPST2-deficient MIA PaCa-2 cells were generated to assess xenograft tumor growth in vivo. Mouse PDAC cells derived from the KrasLSL-G12D/+;Tp53L/+;Pdx1-Cre (KPC) mice were used to generate Tpst2 knockout KPC cells to evaluate tumor growth and metastasis in vivo.

RESULTS

High expressions of SLC35B2 and TPST2 were correlated with poor PDAC patient survival. Knocking down SLC35B2 or TPST2, or pharmacologicically inhibiting sulfation, resulted in the inhibition of PDAC cell proliferation and migration in vitro. TPST2-deficient MIA PaCa-2 cells showed inhibited xenograft tumor growth. Orthotopic inoculation of Tpst2 knockout KPC cells in mice showed inhibition of primary tumor growth, local invasion, and metastasis. Mechanistically, the integrin β4 was found to be a novel substrate of TPST2. Inhibition of sulfation destabilizes integrin β4 protein, which may have accounted for the suppression of metastasis.

CONCLUSIONS

Targeting the SLC35B2-TPST2 axis of tyrosine sulfation may represent a novel approach for therapeutic intervention of PDAC.

Identification of tyrosine sulfation in the variable region of a bispecific antibody and its effect on stability and biological activity

Despite tyrosine sulfation being a relatively common post-translational modification (PTM) on the secreted proteins of higher eukaryotic organisms, there have been surprisingly few reports of this modification occurring in recombinant monoclonal antibodies (mAbs) expressed by mammalian cell lines and even less information regarding its potential impact on mAb efficacy and stability. This discrepancy is likely due to the extreme lability of this modification using many of the mass spectrometry methods typically used within the biopharmaceutical industry for PTM identification, as well as the possible misidentification as phosphorylation. Here, we identified sulfation on a single tyrosine residue located within the identical variable region sequence of a 2 + 1 bispecific mAbs heavy and heavy-heavy chains using a multi-enzymatic approach in combination with mass spectrometry analysis and examined its impact on binding, efficacy, and physical stability. Unlike previous reports, we found that tyrosine sulfation modestly decreased the mAb cell binding and T cell-mediated killing, primarily by increasing the rate of antigen disassociation as determined from surface plasmon resonance-binding experiments. We also found that, while this acidic modification had no significant impact on the mAb thermal stability, sulfation did modestly increase its rate of aggregation, presumably by lowering the mAb's colloidal stability as indicated by polyethylene glycol induced liquid-liquid phase separation experiments.

Comprehensive computational analysis reveals YXXΦ[I/L/M/F/V] motif and YXXΦ-like tetrapeptides across HFRS causing Hantaviruses and their association with viral pathogenesis and host immune regulation

Hemorrhagic fever with renal syndrome (HFRS) is an acute zoonotic disease transmitted through aerosolized excrement of rodents. The etiology of HFRS is complex due to the involvement of viral factors and host immune and genetic factors. The viral species that dominantly cause HFRS are Puumala virus (PUUV), Seoul virus (SEOV), Dobrava-Belgrade virus (DOBV), and Hantaan virus (HTNV). Despite continuous prevention and control measures, HFRS remains a significant public health problem worldwide. The nucleocapsid protein of PUUV, SEOV, DOBV, and HTNV is a multifunctional viral protein involved in various stages of the viral replication cycle. However, the exact role of nucleoproteins in viral pathogenesis is yet to be discovered. Targeting a universal host protein exploited by most viruses would be a game-changing strategy that offers broad-spectrum solutions and rapid epidemic control. The objective of this study is to understand the replication and pathogenesis of PUUV, SEOV, DOBV, and HTNV by targeting tyrosine-based motif (YXXΦ[I/L/M/F/V]) and YXXΦ-like tetrapeptides. In the light of the current study, in silico analysis uncovered many different YXXΦ[I/L/M/F/V] motifs and YXXΦ-like tetrapeptides within nucleoproteins of PUUV, SEOV, DOBV, and HTNV. Following that, the 3D structures of nucleoproteins were predicted using AlphaFold2 to map the location of YXXΦ[I/L/M/F/V] motif and YXXΦ-like tetrapeptides in a 3D environment. Further, in silico analysis and characterization of Post Translational Modifications (PTMs) revealed multiple PTMs sites within YXXΦ[I/L/M/F/V] motif and YXXΦ-like tetrapeptides, which contribute to virulence and host immune regulation. Our study proposed that the predicted YXXΦ[I/L/M/F/V] motif and YXXΦ-like tetrapeptides may confer specific functions such as virulence, host immune regulation, and pathogenesis to nucleoproteins of PUUV, SEOV, DOBV, and HTNV. However, in vivo and in vitro studies on YXXΦ[I/L/M/F/V] motif and YXXΦ-like tetrapeptides will assign new biological roles to these antiviral targets.

From Steroid and Drug Metabolism to Glycobiology, Using Sulfotransferase Structures to Understand and Tailor Function

Sulfotransferases are ubiquitous enzymes that transfer a sulfo group from the universal cofactor donor 3'-phosphoadenosine 5'-phosphosulfate to a broad range of acceptor substrates. In humans, the cytosolic sulfotransferases are involved in the sulfation of endogenous compounds such as steroids, neurotransmitters, hormones, and bile acids as well as xenobiotics including drugs, toxins, and environmental chemicals. The Golgi associated membrane-bound sulfotransferases are involved in post-translational modification of macromolecules from glycosaminoglycans to proteins. The sulfation of small molecules can have profound biologic effects on the functionality of the acceptor, including activation, deactivation, or enhanced metabolism and elimination. Sulfation of macromolecules has been shown to regulate a number of physiologic and pathophysiological pathways by enhancing binding affinity to regulatory proteins or binding partners. Over the last 25 years, crystal structures of these enzymes have provided a wealth of information on the mechanisms of this process and the specificity of these enzymes. This review will focus on the general commonalities of the sulfotransferases, from enzyme structure to catalytic mechanism as well as providing examples into how structural information is being used to either design drugs that inhibit sulfotransferases or to modify the enzymes to improve drug synthesis. SIGNIFICANCE STATEMENT: This manuscript honors Dr. Masahiko Negishi's contribution to the understanding of sulfotransferase mechanism, specificity, and roles in biology by analyzing the crystal structures that have been solved over the last 25 years.

Tyrosine-O-sulfation is a widespread affinity enhancer among thrombin interactors

Tyrosine-O-sulfation is a common post-translational modification (PTM) of proteins following the cellular secretory pathway. First described in human fibrinogen, tyrosine-O-sulfation has long been associated with the modulation of protein-protein interactions in several physiological processes. A number of relevant interactions for hemostasis are largely dictated by this PTM, many of which involving the serine proteinase thrombin (FIIa), a central player in the blood-clotting cascade. Tyrosine sulfation is not limited to endogenous FIIa ligands and has also been found in hirudin, a well-known and potent thrombin inhibitor from the medicinal leech, Hirudo medicinalis. The discovery of hirudin led to successful clinical application of analogs of leech-inspired molecules, but also unveiled several other natural thrombin-directed anticoagulant molecules, many of which undergo tyrosine-O-sulfation. The presence of this PTM has been shown to enhance the anticoagulant properties of these peptides from a range of blood-feeding organisms, including ticks, mosquitos and flies. Interestingly, some of these molecules display mechanisms of action that mimic those of thrombin's bona fide substrates.

Proposed mechanism for rare thrombotic events after use of some Covid-19 vaccines

Administration of AstraZeneca/Oxford and Johnson & Johnson/Janssen Covid-19 vaccines which use an adenovirus vector for DNA delivery has been associated with very rare thromboembolic complications coupled with an immune response to platelet factor 4 protein. The cause of this has not yet been identified. It is known that binding of coagulation factor proteins to the surface of some adenoviruses can protect their function. Here I propose that the thromboembolic events are caused by impairment of coagulation factor X binding to the virus capsid. The unprotected capsid then stimulates an immune response leading to platelet activation, increased thrombogenicity and formation of an antibody complex with platelet factor 4. Impaired binding of factor X may be due to an undiagnosed mutation in affected individuals. Options to test this mechanism experimentally and potential remedial actions to resolve the hazard are described. This mechanism offers a remedial route to address concerns about the safety of these vaccines, which are otherwise well-positioned to deliver global Covid-19 immunity across diverse healthcare economies.

Engineering of a Small Protein Scaffold To Recognize Sulfotyrosine with High Specificity

Protein tyrosine O-sulfation is an essential post-translational modification required for effective biological processes such as hemostasis, inflammatory response, and visual phototransduction. Because of its unstable nature under mass spectrometry conditions and residing on low-abundance cell surface proteins, sulfated tyrosine (sulfotyrosine) residues are difficult to detect or analyze. Enrichment of sulfotyrosine-containing proteins (sulfoproteins) from complex biological samples are typically required before analysis. In this work, we seek to engineer the phosphotyrosine binding pocket of a Src Homology 2 (SH2) domain to act as an antisulfotyrosine antibody mimic. Using tailored selection schemes, several SH2 mutants are identified with high affinity and specificity to sulfotyrosine. Further molecular docking simulations highlight potential mechanisms supporting observed characteristics of these SH2 mutants. Utilities of the evolved SH2 mutants were demonstrated by the detection and enrichment of sulfoproteins.

Functional genetic encoding of sulfotyrosine in mammalian cells

Protein tyrosine O-sulfation (PTS) plays a crucial role in extracellular biomolecular interactions that dictate various cellular processes. It also involves in the development of many human diseases. Regardless of recent progress, our current understanding of PTS is still in its infancy. To promote and facilitate relevant studies, a generally applicable method is needed to enable efficient expression of sulfoproteins with defined sulfation sites in live mammalian cells. Here we report the engineering, in vitro biochemical characterization, structural study, and in vivo functional verification of a tyrosyl-tRNA synthetase mutant for the genetic encoding of sulfotyrosine in mammalian cells. We further apply this chemical biology tool to cell-based studies on the role of a sulfation site in the activation of chemokine receptor CXCR4 by its ligand. Our work will not only facilitate cellular studies of PTS, but also paves the way for economical production of sulfated proteins as therapeutic agents in mammalian systems.

The origins and developments of sulfation-prone tyrosine-rich and acidic N- and C-terminal extensions of class ll and lll small leucine-rich repeat proteins shed light on connective tissue evolution in vertebrates

Background

Small leucine-rich repeat protein (SLRP) family members contain conserved leucine-rich repeat motifs flanked by highly variable N- and C-terminal regions. Most class II and III SLRPs have tyrosine-rich N-terminal regions and some of these are sulfated. However, the evolutionary origin and conservation of the tyrosine-rich and acidic terminal regions remain undetermined. In this study, we present the most comprehensive multiple sequence alignment (MSA) analyses of all eight class II and III SLRPs to date. Based on the level of conservation of tyrosine residues and adjacent sequences, we predict which tyrosine residues are most likely to be sulfated in the terminal regions of human class II and III SLRPs.

Results

Using this novel approach, we predict a total of 22 tyrosine sulfation sites in human SLRPs, of which only 8 sites had been experimentally identified in mammals. Our analyses suggest that sulfation-prone, tyrosine-rich and acidic terminal regions of the class II and III SLRPs emerged via convergent evolution at different stages of vertebrate evolution, coinciding with significant evolutionary events including the development of endochondral bones and articular cartilage, the aquatic to terrestrial transition, and the formation of an amnion.

Conclusions

Our study suggests that selective pressures due to changes in life conditions led to the formation of sulfotyrosine-rich and acidic terminal regions. We believe the independent emergence and evolution of sulfotyrosine-rich and acidic N- and C-terminal regions have provided each class II and III SLRP member with novel vital functions required to develop new specialized extracellular matrices and tissues in vertebrate species.

Engineering of a sulfotyrosine-recognizing small protein scaffold for the study of protein tyrosine O-sulfation

Protein tyrosine O-sulfation is considered as one of the most common types of posttranslational modification of tyrosine in nature. The introduction of a negatively charged sulfate group plays crucial roles in extracellular biomolecular interactions that dictate various cellular processes, including cell adhesion, leukocyte trafficking, hormone activities, and immune responses. Despite substantial advances in our knowledge about protein tyrosine O-sulfation in recent years, our understanding of its biological significance is still in its infancy. This is largely hindered by a chronic lack of suitable biochemical tools. We seek to meet this challenge by engineering a small protein scaffold that can recognize sulfated tyrosine (sulfotyrosine) residues with high affinity. In this chapter, we describe the directed evolution of a Src Homology 2 (SH2) domain to recognize sulfotyrosine. In the first part, the design strategy for the phage display of SH2 variants is discussed. In the second part, the techniques required for phage propagation and selection are described. The evolved SH2 variants are characterized and validated in vitro through fluorescence polarization assays. Finally, the evolved SH2 domain mutants are applied to the visualization of sulfated proteins on the cell surface.

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.

Evolution of Src Homology 2 (SH2) Domain to Recognize Sulfotyrosine

Protein tyrosine O-sulfation is considered as the most common type of post-translational tyrosine modification in nature and plays important roles in extracellular biomolecular interactions. To facilitate the mapping, biological study, and medicinal application of this type of post-translational modification, we seek to evolve a small protein scaffold that recognizes sulfotyrosine with high affinity. We focused our efforts on the engineering of the Src Homology 2 (SH2) domain, which represents the largest class of known phosphotyrosine-recognition domain in nature and has a highly evolvable binding pocket. By using phage display, we successfully engineered the SH2 domain to recognize sulfotyrosine with high affinity. The best mutant, SH2-60.1, displayed more than 1700 fold higher sulfotyrosine-binding affinity than that of the wild-type SH2 domain. We also demonstrated that the evolved SH2 domain mutants could be used to detect sulfoprotein levels on the cell surface. These evolved SH2 domain mutants can be potentially applied to the study of protein tyrosine O-sulfation with proper experimental designs.

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.

Direct identification of tyrosine sulfation by using ultraviolet photodissociation mass spectrometry

Sulfation is a common post-translational modification of tyrosine residues in eukaryotes; however, detection using traditional liquid chromatography-mass spectrometry (LC-MS) methods is challenging based on poor ionization efficiency in the positive ion mode and facile neutral loss upon collisional activation. In the present study, 193 nm ultraviolet photodissociation (UVPD) is applied to sulfopeptide anions to generate diagnostic sequence ions, which do not undergo appreciable neutral loss of sulfate even using higher energy photoirradiation parameters. At the same time, neutral loss of SO₃ is observed from the precursor and charge-reduced precursor ions, a spectral feature that is useful for differentiating tyrosine sulfation from the nominally isobaric tyrosine phosphorylation. LC-MS detection limits for UVPD analysis in the negative mode were determined to be around 100 fmol for three sulfated peptides, caerulein, cionin, and leu-enkephalin. The LC-UVPD-MS method was applied for analysis of bovine fibrinogen, and its key sulfated peptide was confidently identified.

Yolk proteins in the male reproductive system of the fruit fly Drosophila melanogaster: spatial and temporal patterns of expression

In insects, spermatozoa develop in the testes as clones of single spermatogonia covered by specialized somatic cyst cells (cc). Upon completion of spermatogenesis, spermatozoa are released to the vas deferens, while the cc remain in the testes and die. In the fruit fly Drosophila melanogaster, the released spermatozoa first reach the seminal vesicles (SV), the organ where post-testicular maturation begins. Here, we demonstrate the temporal (restricted to the evening and early night hours) accumulation of membranous vesicles containing proteins in the SV lumen of D. melanogaster. When SV vesicles were isolated from the semen and co-incubated with testis-derived spermatozoa in vitro, their contents bound to the spermatozoa along their tails. The proteins of the SV vesicles were then characterized using 2-D electrophoresis. We identified a prominent protein spot of around 45-47 kDa, which disappears from the SV vesicles in the night, i.e. shortly after they appear in the SV lumen. Sequencing of peptides derived from this spot by mass spectrometry revealed identity with three yolk proteins (YP1-3). This unexpected result was confirmed by western blotting, which demonstrated that SV vesicles contain proteins that are immunoreactive with an antibody against D. melanogaster YP1-3. The expression of all yp genes was shown to be a unique feature of testis tissues. Using RNA probes we found that their transcripts localize exclusively to the cc that cover fully developed spermatozoa in the distal part of each testis. Temporally, the expression of yp genes was found to be restricted to a short period during the day and is followed by the evening accumulation of YP proteins in the cc. Immunohistochemical staining confirmed that cc are the source of SV vesicles containing YPs that are released into the SV lumen. These vesicles interact with spermatozoa and as a result, YPs become extrinsic proteins of the sperm membrane. Thus, we describe for the first time the expression of yolk proteins in the male reproductive system of D. melanogaster under physiological conditions, and show that somatic cells of the testes are the source of these proteins.

The Role of RaxST, a Prokaryotic Sulfotransferase, and RaxABC, a Putative Type I Secretion System, in Activation of the Rice XA21-Mediated Immune Response

Tyrosine sulfation is an important posttranslational modification that determines the outcome of serious diseases in plants and animals. We have recently demonstrated that the plant pathogen Xanthomonas oryzae pv. oryzae (Xoo) carries a functional sulfotransferase (RaxST). raxST is required for activation of rice Xa21-mediated immunity indicating the critical, but unknown, function of raxST in mediating the Xoo/rice interaction. The raxST gene resides in the same operon (raxSTAB) as components of a predicted type I secretion and processing system (RaxA and RaxB). These observations suggest a model where RaxST sulfates a molecule that contains a leader peptide, which is cleaved by the peptidase domain of the RaxB protein and secreted outside the bacterial cell by the RaxABC T1SS.

Tyrosylprotein sulfotransferase-1 and tyrosine sulfation of chemokine receptor 4 are induced by Epstein-Barr virus encoded latent membrane protein 1 and associated with the metastatic potential of human nasopharyngeal carcinoma

The latent membrane protein 1 (LMP1), which is encoded by the Epstein-Barr virus (EBV), is an important oncogenic protein that is closely related to carcinogenesis and metastasis of nasopharyngeal carcinoma (NPC), a prevalent cancer in China. We previously reported that the expression of the functional chemokine receptor CXCR4 is associated with human NPC metastasis. In this study, we show that LMP1 induces tyrosine sulfation of CXCR4 through tyrosylprotein sulfotransferase-1 (TPST-1), an enzyme that is responsible for catalysis of tyrosine sulfation in vivo, which is likely to contribute to the highly metastatic character of NPC. LMP1 could induce tyrosine sulfation of CXCR4 and its associated cell motility and invasiveness in a NPC cell culture model. In contrast, the expression of TPST-1 small interfering RNA reversed LMP1-induced tyrosine sulfation of CXCR4. LMP1 conveys signals through the epidermal growth factor receptor (EGFR) pathway, and EGFR-targeted siRNA inhibited the induction of TPST-1 by LMP1. We used a ChIP assay to show that EGFR could bind to the TPST-1 promoter in vivo under the control of LMP1. A reporter gene assay indicated that the activity of the TPST-1 promoter could be suppressed by deleting the binding site between EGFR and TPST-1. Finally, in human NPC tissues, the expression of TPST-1 and LMP1 was directly correlated and clinically, the expression of TPST-1 was associated with metastasis. These results suggest the up-regulation of TPST-1 and tyrosine sulfation of CXCR4 by LMP1 might be a potential mechanism contributing to NPC metastasis.

PredSulSite: prediction of protein tyrosine sulfation sites with multiple features and analysis

Tyrosine sulfation is a ubiquitous posttranslational modification that regulates extracellular protein-protein interactions, intracellular protein transportation modulation, and protein proteolytic process. However, identifying tyrosine sulfation sites remains a challenge due to the lability of sulfation sequences. In this study, we developed a method called PredSulSite that incorporates protein secondary structure, physicochemical properties of amino acids, and residue sequence order information based on support vector machine to predict sulfotyrosine sites. Three types of encoding algorithms-secondary structure, grouped weight, and autocorrelation function-were applied to mine features from tyrosine sulfation proteins. The prediction model with multiple features achieved an accuracy of 92.89% in 10-fold cross-validation. Feature analysis showed that the coil structure, acidic amino acids, and residue interactions around the tyrosine sulfation sites all contributed to the sulfation site determination. The detailed feature analysis in this work can help us to understand the sulfation mechanism and provide guidance for the related experimental validation. PredSulSite is available as a community resource at http://www.bioinfo.ncu.edu.cn/inquiries_PredSulSite.aspx.

Catalytic mechanism of Golgi-resident human tyrosylprotein sulfotransferase-2: a mass spectrometry approach

Human tyrosylprotein sulfotransferases catalyze the transfer of a sulfuryl moiety from the universal sulfate donor PAPS to the hydroxyl substituent of tyrosine residues in proteins and peptides to yield tyrosine sulfated products and PAP. Tyrosine sulfation occurs in the trans-Golgi network, affecting an estimated 1% of the tyrosine residues in all secreted and membrane-bound proteins in higher order eukaryotes. In this study, an effective LC-MS-based TPST kinetics assay was developed and utilized to measure the kinetic properties of human TPST-2 and investigate its catalytic mechanism when G protein-coupled CC-chemokine receptor 8 (CCR8) peptides were used as acceptor substrates. Through initial rate kinetics, product inhibition studies, and radioactive-labeling experiments, our data strongly suggest a two-site ping-pong model for TPST-2 action. In this mechanistic model, the enzyme allows independent binding of substrates to two distinct sites, and involves the formation of a sulfated enzyme covalent intermediate. Some insights on the important amino acid residues at the catalytic site of TPST-2 and its covalent intermediate are also presented. To our knowledge, this is the first detailed study of the reaction kinetics and mechanism reported for human TPST-2 or any other Golgi-resident sulfotransferase.

Tyrosylprotein sulfotransferase regulates collagen secretion in Caenorhabditis elegans

The sulfation of tyrosine residues is an important post-translational modification involved in the regulation of protein function. We examined the activity of worm tyrosylprotein sulfotransferase (TPST-1) on a typical cuticle collagen, ROL-6, in C. elegans. We verified that TPST-1 sulfates three tyrosine residues of ROL-6 in vitro. We found that these tyrosine residues are important for the secretion of ROL-6::GFP. Mutant ROL-6::GFP proteins that contain more than two substitutions of the target tyrosine residues are severely deficient in cuticle localization. Consistently, knock down of tpst-1 blocked the cuticle localization of ROL-6::GFP. Therefore, the sulfation of ROL-6 by TPST-1 is critical for the proper localization of ROL-6. We also confirmed that worm TPST-1 is localized to the trans-Golgi network (TGN). Our results indicate that TPST-1 regulates cuticle organization by promoting the transport of ROL-6 from the TGN to the cuticle.

Comparative and functional genomics of lipases in holometabolous insects

Lipases have key roles in insect lipid acquisition, storage and mobilisation and are also fundamental to many physiological processes underpinning insect reproduction, development, defence from pathogens and oxidative stress, and pheromone signalling. We have screened the recently sequenced genomes of five species from four orders of holometabolous insects, the dipterans Drosophila melanogaster and Anopheles gambiae, the hymenopteran Apis mellifera, the moth Bombyx mori and the beetle Tribolium castaneum, for the six major lipase families that are also found in other organisms. The two most numerous families in the insects, the neutral and acid lipases, are also the main families in mammals, albeit not in Caenorhabditis elegans, plants or microbes. Total numbers of the lipases vary two-fold across the five insect species, from numbers similar to those in mammals up to numbers comparable to those seen in C. elegans. Whilst there is a high degree of orthology with mammalian lipases in the other four families, the great majority of the insect neutral and acid lipases have arisen since the insect orders themselves diverged. Intriguingly, about 10% of the insect neutral and acid lipases have lost motifs critical for catalytic function. Examination of the length of lid and loop regions of the neutral lipase sequences suggest that most of the insect lipases lack triacylglycerol (TAG) hydrolysis activity, although the acid lipases all have intact cap domains required for TAG hydrolysis. We have also reviewed the sequence databases and scientific literature for insights into the expression profiles and functions of the insect neutral and acid lipases and the orthologues of the mammalian adipose triglyceride lipase which has a pivotal role in lipid mobilisation. These data suggest that some of the acid and neutral lipase diversity may be due to a requirement for rapid accumulation of dietary lipids. The different roles required of lipases at the four discrete life stages of holometabolous insects may also contribute to the diversity of lipases required by insects. In addition, insects use lipases to perform roles for which there are no correlates in mammals, including as yolk and male accessory gland proteins.

Sulfation of eggshell components by Pipe defines dorsal-ventral polarity in the Drosophila embryo

Drosophila embryonic dorsal-ventral (DV) polarity is controlled by a group of sequentially acting serine proteases located in the fluid-filled perivitelline space between the embryonic membrane and the eggshell, which generate the ligand for the Toll receptor on the ventral side of the embryo. Spatial control of the protease cascade relies on the Pipe sulfotransferase, a fly homolog of vertebrate glycosaminoglycan-modifying enzymes, which is expressed in ventral cells of the follicular epithelium surrounding the developing oocyte. Here we show that the vitelline membrane-like (VML) protein undergoes Pipe-dependent sulfation and, consistent with a role in conveying positional information from the egg chamber to the embryo, becomes incorporated into the eggshell at a position corresponding to the location of the follicle cells from which it was secreted. Although VML influences embryonic DV pattern in a sensitized genetic background, VML is not essential for DV axis formation, suggesting that there is redundancy in the composition of the Pipe enzymatic target. Correspondingly, we find that additional structural components of the vitelline membrane undergo Pipe-dependent sulfation. In identifying the elusive targets of Pipe, this work points to the vitelline membrane as the source of signals that generate the Drosophila DV axis.

A target-specific approach for the identification of tyrosine-sulfated hemostatic proteins

A simple methodology for the identification of hemostatic proteins that are subjected to posttranslational tyrosine sulfation was developed. The procedure involves sequence analysis of members of the three hemostatic pathways using the Sulfinator prediction algorithm, followed by [(35)S]sulfate labeling of cultured HepG2 human hepatoma cells, immunoprecipitation of targeted [(35)S]sulfate-labeled hemostatic proteins, and tyrosine O-[(35)S]sulfate analysis of immunoprecipitated proteins. Three new tyrosine-sulfated hemostatic proteins-protein S, prekallikrein, and plasminogen-were identified. Such a target-specific approach will allow investigation of tyrosine-sulfated proteins of other biochemical/physiological pathways/processes and contribute to a better understanding of the functional role of posttranslational tyrosine sulfation.

Sulfated tyrosines 27 and 29 in the N-terminus of human CXCR3 participate in binding native IP-10

AIM

Human CXCR3, a seven-transmembrane segment (7TMS), is predominantly expressed in Th1-mediated responses. Interferon-gamma-inducible protein 10 (IP-10) is an important ligand for CXCR3. Their interaction is pivotal for leukocyte migration and activation. Tyrosine sulfation in 7TMS is a posttranslational modification that contributes substantially to ligand binding. We aimed to study the role of tyrosine sulfation of CXCR3 in the protein's binding to IP-10.

METHODS

Plasmids encoding CXCR3 and its mutants were prepared by PCR and site-directed mutagenesis. HEK 293T cells were transfected with plasmids encoding CXCR3 or its variants using calcium phosphate. Transfected cells were labeled with [(35)S]-cysteine and methionine or [(35)S]-Na(2)SO(3) and then analyzed by immunoprecipitation to measure sulfation. Experiments with (125)I-labeled IP-10 were carried out to evaluate the affinity of CXCR3 for its ligand. Calcium influx assays were used to measure intercellular signal transduction.

RESULTS

Our data show that sulfate moieties are added to tyrosines 27 and 29 of CXCR3. Mutation of these two tyrosines to phenylalanines substantially decreases binding of CXCR3 to IP-10 and appears to eliminate the associated signal transduction. Tyrosine sulfation of CXCR3 is enhanced by tyrosyl protein sulfotransferases (TPSTs), and it is weakened by shRNA constructs. The binding ability of CXCR3 to IP-10 is increased by TPSTs and decreased by shRNAs.

CONCLUSIONS

This study identifies two sulfated tyrosines in the N-terminus of CXCR3 as part of the binding site for IP-10, and it underscores the fact that tyrosine sulfation in the N-termini of 7TMS receptors is functionally important for ligand interactions. Our study suggests a molecular target for inhibiting this ligand-receptor interaction.

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.

Toward a framework for sulfoproteomics: Synthesis and characterization of sulfotyrosine-containing peptides

Tyrosine sulfation is one of the most common post-translational modifications in secreted and transmembrane proteins and a key modulator of extracellular protein-protein interactions. Several proteins known to be tyrosine sulfated play important roles in physiological processes, and in some cases a direct link between protein function and tyrosine sulfation has been established. In blood coagulation, tyrosine sulfation of factor VIII is required for efficient binding of von Willebrand factor; in leukocyte adhesion, tyrosine sulfation of the P-selectin glycoprotein ligand-1 mediates high-affinity binding to P-selectin; and in leukocyte chemotaxis, tyrosine sulfation of chemokine receptors is required for optimal interaction with chemokine ligands. Furthermore, tyrosine sulfation has been implicated in several infectious diseases. In particular, tyrosine sulfation of the HIV-1 co-receptor CCR5 is required for viral entry into host cells and tyrosine sulfation of the Duffy antigen/receptor for chemokines is crucial for erythrocyte invasion by the malaria parasite plasmodium vivax. Despite increasing interest in tyrosine sulfation in recent years, the sulfoproteome still remains largely unexplored. To date, only a relatively small number of sulfotyrosine-containing peptides and proteins have been identified, and a specific role for tyrosine sulfation has not been established for most of these. Here, we provide an overview of the biology and enzymology of tyrosine sulfation and discuss recent developments in preparative and analytical methods that are central to sulfoproteome research.

Stability of tyrosine sulfate in acidic solutions

Tyrosine O-sulfation is a posttranslational modification of secretory and membrane proteins transported through the Golgi apparatus, which is widespread among higher eukaryotes. O-Sulfated tyrosines are not immediately identified during sequencing of peptides and proteins, because the sulfate ester is acid labile and rapidly hydrolyses to tyrosine in strong acidic solutions. Little is known about the hydrolysis at mildly acidic solutions, which are used during several protein purification and analysis procedures. We have examined the stability of tyrosine sulfate using sulfated gastrin-17, caerulein, and drosulfokinin as models for tyrosine O-sulfated peptides. The peptides were incubated in acidic solutions in a pH range of 1 to 3 at different temperatures and time spans. Only marginal hydrolysis of gastrin-17 was observed in triflouroacetic acid at room temperature or below. Comparison of the acid hydrolysis of the three peptides showed that hydrolysis rate depends mainly on the primary amino acid composition of the peptide. The activation energy (E(a)) for the hydrolysis of sulfated gastrin-17 was found to be E(a)=98.7+/-5 kJ mol(-1). This study serves as a general reference for handling tyrosine sulfated peptides in aqueous acidic solutions. We conclude that tyrosine sulfate is more stable under normal protein purification conditions than previously assumed.

Protein sulfation analysis—A primer

The aim of this review is to present an overview of protein sulfation in the context of 'modificomics', i.e. post-translational modification-specific proteome research. In addition to a short introduction to the biology of protein sulfation (part 1), we will provide detailed discussion regarding (i) methods and tools for prediction of protein tyrosine sulfation sites (part 2), (ii) biochemical techniques used for protein sulfation analysis (part 3.1), and (iii) mass spectrometric strategies and methods applied to protein sulfation analysis (part 3.2). We will highlight strengths and limitations of different strategies and approaches (including references), providing a primer for newcomers to protein sulfation analysis.

C alpha-C backbone fragmentation dominates in electron detachment dissociation of gas-phase polypeptide polyanions

Fragmentation of peptide polyanions by electron detachment dissociation (EDD) has been induced by electron irradiation of deprotonated polypeptides [M-nH](n-) with >10 eV electrons. EDD has been found to lead preferentially to a* and x fragment ions (C(alpha)-C backbone cleavage) arising from the dissociation of oxidized radical anions [M-nH]((n-1)-*. We demonstrate that C(alpha)-C cleavages, which are otherwise rarely observed in tandem mass spectrometry, can account for most of the backbone fragmentation, with even-electron x fragments dominating over radical a* ions. Ab initio calculations at the B3 LYP level of theory with the 6-311+G(2 p,2 d)//6-31+G(d,p) basis set suggested a unidirectional mechanism for EDD (cleavage always N-terminal to the radical site), with a*, x formation being favored over a, x* fragmentation by 74.2 kJ mol(-1). Thus, backbone C(alpha)-C bonds N-terminal to proline residues should be immune to EDD, in agreement with the observations. EDD may find application in mass spectrometry for such tasks as peptide sequencing and localization of labile post-translational modifications, for example, those introduced by sulfation and phosphorylation. EDD can now be performed not only in Fourier transform mass spectrometry, but also in far more widely used quadrupole (Paul) ion traps.

Recognition of a CXCR4 sulfotyrosine by the chemokine stromal cell-derived factor-1alpha (SDF-1alpha/CXCL12)

Tyrosine sulfation of the chemokine receptor CXCR4 enhances its interaction with the chemokine SDF-1alpha. Given similar post-translational modification of other receptors, including CCR5, CX3CR1 and CCR2b, tyrosine sulfation may be of universal importance in chemokine signaling. N-terminal domains from seven transmembrane chemokine receptors have been employed for structural studies of chemokine-receptor interactions, but never in the context of proper post-translational modifications known to affect function. A CXCR4 peptide modified at position 21 by expressed tyrosylprotein sulfotransferase-1 and unmodified peptide are both disordered in solution, but bind SDF-1alpha with low micromolar affinities. NMR and fluorescence polarization measurements showed that the CXCR4 peptide stabilizes dimeric SDF-1alpha, and that sulfotyrosine 21 binds a specific site on the chemokine that includes arginine 47. We conclude that the SDF-1alpha dimer preferentially interacts with receptor peptide, and residues beyond the extreme N-terminal region of CXCR4, including sulfotyrosine 21, make specific contacts with the chemokine ligand.

CC and CX3C chemokines differentially interact with the N terminus of the human cytomegalovirus-encoded US28 receptor

Human cytomegalovirus (HCMV) is the causative agent of life-threatening systemic diseases in immunocompromised patients as well as a risk factor for vascular pathologies, like atherosclerosis, in immunocompetent individuals. HCMV encodes a G-protein-coupled receptor (GPCR), referred to as US28, that displays homology to the human chemokine receptor CCR1 and binds several chemokines of the CC family as well as the CX3C chemokine fractalkine with high affinity. Most importantly, following HCMV infection, US28 activates several intracellular pathways, either constitutively or in a chemokine-dependent manner. In this study, our goal was to understand the molecular interactions between chemokines and the HCMV-encoded US28 receptor. To achieve this goal, a double approach has been used, consisting in the analysis of both receptor and ligand mutants. This approach has led us to identify several amino acids located in the N terminus of US28 that differentially contribute to the high affinity binding of CC versus CX3C chemokines. Additionally, our results highlight the importance of secondary modifications occurring at US28, such as sulfation, for ligand recognition. Finally, the effects of chemokine dimerization and interaction with glycosaminoglycans (GAGs) on chemokine binding and activation of US28 were investigated as well using CCL4 as model ligand. In line with the two-state model describing chemokine/receptor interaction, we show that an aromatic residue in the N-loop region of CCL4 promotes tight binding to US28, whereas receptor activation depends on the presence of the N terminus of CCL4, as shown previously for CCR5.

Sulfation of tyrosine 174 in the human C3a receptor is essential for binding of C3a anaphylatoxin

The complement anaphylatoxin C3a and its cellular seven-transmembrane segment receptor, C3aR, are implicated in a variety of pathological inflammatory processes. C3aR is a G-protein-coupled receptor with an exceptionally large second extracellular loop of 172 amino acids. Previously reported deletion studies have shown that at least part of this region plays a critical role in binding C3a. Our data now demonstrate that five tyrosines in the second extracellular loop of the C3aR are posttranslationally modified by the addition of sulfate. Blocking sulfation by mutation of tyrosine to phenylalanine at positions 184, 188, 317, and/or 318 does not affect ligand binding or signal transduction. However, when tyrosine 174 is mutated to phenylalanine, binding of native C3a is completely blocked. This variant efficiently mobilizes calcium in response to synthetic C3a agonist peptides, but not to native C3a. This finding is consistent with a two-site model of ligand association typical of many peptide ligand-receptor interactions and identifies sulfotyrosine 174 as the critical C3a docking site. Tyrosine sulfation in the amino-terminal extracellular domain has been shown to be important in several other seven-transmembrane segment receptors. Our data now demonstrate that tyrosine sulfate in other extracellular domains can function for ligand interactions as well.

Tyrosine sulfation of CCR5 N-terminal peptide by tyrosylprotein sulfotransferases 1 and 2 follows a discrete pattern and temporal sequence

The CC-chemokine receptor 5 (CCR5) is the major coreceptor for the entry of macrophage-tropic (R5) HIV-1 strains into target cells. Posttranslational sulfation of tyrosine residues in the N-terminal tail of CCR5 is critical for high affinity interaction of the receptor with the HIV-1 envelope glycoprotein gp120 in complex with CD4. Here, we focused on defining precisely the sulfation pattern of the N terminus of CCR5 by using recombinant human tyrosylprotein sulfotransferases TPST-1 and TPST-2 to modify a synthetic peptide that corresponds to amino acids 2-18 of the receptor (CCR5 2-18). Analysis of the reaction products was made with a combination of reversed-phase HPLC, proteolytic cleavage, and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS). We found that CCR5 2-18 is sulfated by both TPST isoenzymes leading to a final product with four sulfotyrosine residues. Sulfates were added stepwise to the peptide producing specific intermediates with one, two, or three sulfotyrosines. The pattern of sulfation in these intermediates suggests that Tyr-14 and Tyr-15 are sulfated first, followed by Tyr-10, and finally Tyr-3. These results represent a detailed analysis of the multiple sulfation reaction of a peptide substrate by TPSTs and provide a structural basis for understanding the role of tyrosine sulfation of CCR5 in HIV-1 coreceptor and chemokine receptor function.

Differential sorting of constitutively co-secreted proteins in the ovarian follicle cells of Drosophila

Conventional and freeze-fracture electron microscopy, immuno-electron microscopy of ovarian cryosections and confocal immunofluorescence were used to analyze the ovarian distribution of the major protein classes being secreted by the follicle cells during the vitellogenic and choriogenic stages of Drosophila oogenesis. Our results clearly demonstrated that at vitellogenic stages the follicle cells co-secrete constitutively vitelline membrane and yolk proteins that are either sorted into distinct secretory vesicles or they are segregated in different parts of bipartite vesicles by differential condensation. Following their exocytosis only the vitelline membrane proteins are incorporated into the forming vitelline membrane. The yolk proteins (along with their hemolymph circulating counterparts) diffuse through gaps amongst the incomplete vitelline membrane and are internalized through endocytosis by the oocyte where they are finally stored into modified lysosomes referred to as alpha-yolk granules. The unexpected immunolocalization of vitelline membrane antigens in the associated body of the alpha-yolk granules may indicate that this structure is a transient repository for the proteins being internalized into the oocyte along with the yolk proteins. In the early choriogenic follicle cells the vitelline membrane and early chorion proteins were found to be co-secreted and to be evenly intermixed into the same secretory vesicles. These findings illuminate new details concerning the follicle cells secretory and oocyte endocytic pathways and provide for the first time evidence for condensation-mediated sorting of constitutively secreted proteins in Drosophila.

Vitellogenin is glycosylated in the fat body of the stick insect Carausius morosus and not further modified upon transfer to the ovarian follicle

Synthesis and secretion of vitellogenin (Vg) polypeptides were studied in egg-laying females of the stick insect Carausius morosus following in vivo exposure to [35S]-methionine and acetyl-N-[3H]-glucosamine. The specificity of radioisotope incorporation was assessed by in vitro inhibition with tunicamycin and carbohydrate extraction with endo-glycosidase H. Vg polypeptides change in molecular weight during synthesis in the fat body and are not further modified upon transfer to the haemolymph or to the oocyte, suggesting that they are already fully glycosylated prior to secretion. Radioactivity in the fat body was initially distributed over cisternae of the rough endoplasmic reticulum and gradually transferred to the Golgi apparatus. Within an hour of exposure, electron-dense granules budding from the trans-Golgi network became preferentially labeled. Radioactivity in the ovarian follicle was restricted to the yolk granules of the cortical ooplasm and to the amorphous material lying within the intercellular channels of the follicular epithelium. This amorphous material was also shown to react positively when tested with a monoclonal antibody raised specifically against a Vg polypeptide.

Phosphorylation polymorphism in the yolk protein 2 of Drosophila hawaiiensis

An intraspecific polymorphism in the electrophoretic migration pattern of the yolk proteins in D. hawaiiensis was established and characterized. The polymorphism includes yolk protein migration patterns of two, three, or four bands by polyacrylamide gel electrophoresis. Peptide mapping analysis demonstrates that in the two band migration pattern YP2 comigrates with YP3, whereas in the three and four band migration patterns YP2 migrates between YP1 and YP3 in addition to comigrating with YP3. It further demonstrates that the top two bands of the four band migration pattern consists of YP1. Phosphatase treatment of the yolk proteins establishes that the different electrophoretic migration patterns of YP2 are caused by different degrees of phosphorylation. It is suggested that the YP1 polymorphism is caused by a yp1 gene modification and that the YP2 polymorphism is caused by two different post-translational processing paths.

New consensus features for tyrosine O-sulfation determined by mutational analysis

Tyrosine sulfation is an ubiquitous modification of proteins synthesized along the secretory pathway. It enhances protein-protein interactions and may be necessary for the bioactivity of secreted proteins and peptides. To predict tyrosine sulfation, a consensus has been proposed based on sequence comparisons of known substrates and on in vitro studies using synthetic peptides. This consensus predicts the presence of acidic residues on the amino-terminal side of the target tyrosine as the key feature. Using site-directed mutagenesis, we have examined the role of residues neighboring the sulfation site of an intact protein, human progastrin, in vivo. The results show that the charge of the residue in the amino-terminal position (-1) of the tyrosine is critical and can be neutral or acidic, whereas a basic residue abolishes sulfation. In addition, the degree of sulfation is influenced by the residues in positions -2 and -3. Hence, surprisingly a basic residue in position -2 enhances sulfation. Our data suggest a considerably broader range of substrates for the tyrosylprotein sulfotransferase than hitherto assumed and that the tyrosylprotein sulfotransferase is cell-specifically expressed.

Estrone sulfatase: probing structural requirements for substrate and inhibitor recognition

The enzyme-catalyzed desulfation of steroids is a transformation that plays an important role in steroid biosynthesis. Conversion of steroid sulfates to unconjugated steroids may provide a source of steroids for processes such as steroid transport and the growth and proliferation of breast cancer. Steroid sulfatase catalyzes the hydrolysis of 3beta-hydroxysteroid sulfates. To identify structural features important in enzyme-inhibitor interaction, a variety of steroidal and non-steroidal phosphate esters were synthesized and tested as inhibitors of steroid sulfatase activity. We report that the basic structure for enzyme-inhibitor binding does not include the steroid nucleus. Furthermore, the hydrophobicity of the non-steroidal phosphates was determined to be an important factor for optimal inhibition. The monoanionic form of the phosphorylated compounds was found to be the inhibitory species. The best non-steroidal inhibitor of steroid sulfatase activity was n-lauroyl tryamine phosphate with a Ki of 3.6 microM and 520 nM at pH 7.5 and 7.0. The poorest non-steroidal based inhibitor of sulfatase activity was tetrahydronaphthyl phosphate with a Ki of 870 and 360 microM at pH 7.5 and 7.0.