Glycosylphosphatidylinositol Anchor Research Articles

A genetic screen identifies a protective type III interferon response to Cryptosporidium that requires TLR3 dependent recognition.

Cryptosporidium is a leading cause of severe diarrhea and diarrheal-related death in children worldwide. As an obligate intracellular parasite, Cryptosporidium relies on intestinal epithelial cells to provide a niche for its growth and survival, but little is known about the contributions that the infected cell makes to this relationship. Here we conducted a genome wide CRISPR/Cas9 knockout screen to discover host genes that influence Cryptosporidium parvum infection and/or host cell survival. Gene enrichment analysis indicated that the host interferon response, glycosaminoglycan (GAG) and glycosylphosphatidylinositol (GPI) anchor biosynthesis are important determinants of susceptibility to C. parvum infection and impact on the viability of host cells in the context of parasite infection. Several of these pathways are linked to parasite attachment and invasion and C-type lectins on the surface of the parasite. Evaluation of transcript and protein induction of innate interferons revealed a pronounced type III interferon response to Cryptosporidium in human cells as well as in mice. Treatment of mice with IFNλ reduced infection burden and protected immunocompromised mice from severe outcomes including death, with effects that required STAT1 signaling in the enterocyte. Initiation of this type III interferon response was dependent on sustained intracellular growth and mediated by the pattern recognition receptor TLR3. We conclude that host cell intrinsic recognition of Cryptosporidium results in IFNλ production critical to early protection against this infection.

Molecular insights into biogenesis of glycosylphosphatidylinositol anchor proteins

Eukaryotic cells are coated with an abundance of glycosylphosphatidylinositol anchor proteins (GPI-APs) that play crucial roles in fertilization, neurogenesis, and immunity. The removal of a hydrophobic signal peptide and covalent attachment of GPI at the new carboxyl terminus are catalyzed by an endoplasmic reticulum membrane GPI transamidase complex (GPI-T) conserved among all eukaryotes. Here, we report the cryo-electron microscopy (cryo-EM) structure of the human GPI-T at a global 2.53-Å resolution, revealing an equimolar heteropentameric assembly. Structure-based mutagenesis suggests a legumain-like mechanism for the recognition and cleavage of proprotein substrates, and an endogenous GPI in the structure defines a composite cavity for the lipid substrate. This elongated active site, stemming from the membrane and spanning an additional ~22-Å space toward the catalytic dyad, is structurally suited for both substrates which feature an amphipathic pattern that matches this geometry. Our work presents an important step towards the mechanistic understanding of GPI-AP biosynthesis.

The Effect of Honey Bee Venom on CD14 Protein Expression as Monocyte Marker in D-Alpha-Tocopheryl Succinate (Vitamin E)-Treated HL-60 Cells

Background: The membrane form of a Cluster of Differentiation 14 (CD14) is anchored to the phospholipid bilayer via glycosylphosphatidylinositol anchor. This molecule is expressed on the intrinsic surface of monocytes and neutrophils. This protein is not expressed on the HL60 cell surface. It is believed that the differentiation of HL-60 cells stops in the promyelocytic stage. The differentiation of HL-60 cells with compounds such as vitamin A, D, E results in membrane CD14 expression.
 Objectives: The objective of this study was an evaluation of CD14 expression by Honey Bee Venom (HBV) in HL60 cells treated by D-alpha-Tocopheryl Succinate (D-α-TS). Methods: HL-60 cells were cultured in RPMI Media 1640 medium and treated with different concentrations of D-α-TS and HBV. Cellular differentiation was tested by Nitro Blue Tetrazolium (NBT) staining, immunocytochemistry, and flow cytometry. The studied data were analyzed using one-way analysis of variance and InStat 3 software.
 Methods: HL-60 cells were cultured in RPMI medium and treated with different concentrations of D-α-TS and HBV. Cellular differentiation was tested by NBT staining, immunocytochemistry, and flow cytometry. The studied data were analyzed using one-way analysis of variance and InStat 3 software.
 Results: MTT assay demonstrated that HBV and D-alpha-tocopheryl induce death in HL-60 cell lines in a time and dose-dependent manner. Also, Wright-Giemsa, NBT staining showed morphologically differentiation. Immunocytochemistry and flow cytometry analysis shows that cells treated with 6 µg/mL D-α-TS and 2.5 µg/mL HBV for 5 days significantly increase the expression of CD14 in HL-60 compared to cells treated with D-α-TS.
 Conclusion: HBV can induce cell death and inhibit cell proliferation. Also, increase differentiation potency of D-α-TS via HBV can increase the differentiation by inhibiting NFκB and COX-2 and increasing the expression of P21 that plays an essential role in increasing CD14 protein expression and subsequently induce differentiation in HL-60 cells to monocytes.

Establishment and Application of an Indirect Enzyme-Linked Immunosorbent Assay for Measuring GPI-Anchored Protein 52 (P52) Antibodies in Babesia gibsoni-Infected Dogs.

Simple SummaryIn this study, a novel BgGPI52-WH antigen was identified and evaluated as an immunodiagnostic candidate. An indirect ELISA was established based on the BgGPI52-WH antigen. The results showed that the iELISA had good sensitivity, specificity and reproducibility, and the signal could be detected as early as the sixth day after infection. Clinical samples were tested using the established method, and 11.41% of the samples were positive. The results suggested that BgGPI52-WH is a good immunodiagnostic marker and the iELISA is a practical method for early diagnosis.Babesia gibsoni is a malaria-like protozoan that parasitizes the red blood cells of canids to cause babesiosis. Due to its high expression and essential function in the survival of parasites, the Glycosylphosphatidylinositol (GPI) anchor protein family is considered an excellent immunodiagnostic marker. Herein, we identified a novel GPI-anchored protein named as BgGPI52-WH with a size of 52 kDa; the recombinant BgGPI52-WH with high antigenicity and immunogenicity was used as a diagnostic antigen to establish a new iELISA method. The iELISA had a sensitivity of 1:400, and no cross-reaction with other apicomplexan parasites occurred. We further demonstrated that the degree of variation was less than 10% using the same samples from the same or different batches of an enzyme-labeled strip. It was found that the method was able to detect early infection (6 days after infection) in the sera of the B. gibsoni-infected experimental dogs in which antibody response to rBgGPI52-WH was evaluated. Clinical sera from pet hospitals were further tested, and the average positive rate was about 11.41% (17/149). The results indicate that BgGPI52-WH is a reliable diagnostic antigen, and the new iELISA could be used as a practical method for the early diagnosis of B. gibsoni.

Novel Polymorphisms and Genetic Characteristics of the Shadow of Prion Protein Gene (SPRN) in Cats, Hosts of Feline Spongiform Encephalopathy.

Prion diseases are transmissible spongiform encephalopathies (TSEs) caused by pathogenic prion protein (PrPSc) originating from normal prion protein (PrPC) and have been reported in several types of livestock and pets. Recent studies have reported that the shadow of prion protein (Sho) encoded by the shadow of prion protein gene (SPRN) interacts with prion protein (PrP) and accelerates prion diseases. In addition, genetic polymorphisms in the SPRN gene are related to susceptibility to prion diseases. However, genetic polymorphisms in the feline SPRN gene and structural characteristics of the Sho have not been investigated in cats, a major host of feline spongiform encephalopathy (FSE). We performed amplicon sequencing to identify feline SPRN polymorphisms in the 623 bp encompassing the open reading frame (ORF) and a small part of the 3′ untranslated region (UTR) of the SPRN gene. We analyzed the impact of feline SPRN polymorphisms on the secondary structure of SPRN mRNA using RNAsnp. In addition, to find feline-specific amino acids, we carried out multiple sequence alignments using ClustalW. Furthermore, we analyzed the N-terminal signal peptide and glycosylphosphatidylinositol (GPI)-anchor using SignalP and PredGPI, respectively. We identified three novel SNPs in the feline SPRN gene and did not find strong linkage disequilibrium (LD) among the three SNPs. We found four major haplotypes of the SPRN polymorphisms. Strong LD was not observed between PRNP and SPRN polymorphisms. In addition, we found alterations in the secondary structure and minimum free energy of the mRNA according to the haplotypes in the SPRN polymorphisms. Furthermore, we found four feline-specific amino acids in the feline Sho using multiple sequence alignments among several species. Lastly, the N-terminal signal sequence and cutting site of the Sho protein of cats showed similarity with those of other species. However, the feline Sho protein exhibited the shortest signal sequence and a unique amino acid in the omega-site of the GPI anchor. To the best of our knowledge, this is the first report on genetic polymorphisms of the feline SPRN gene.

Design and synthesis of 4-azido-phosphatidylinositol as a potential probe for metabolic engineering of glycosylphosphatidylinositol on cells

A diacyl phosphatidylinositol (PI) derivative with an azide linked to its inositol C4-position was effectively synthesized in 19 steps for the longest linear sequence and in a ca. 1% overall yield from 1,2-distearoyl-sn-glycerol and D-glucose. This compound was designed as a biosynthetic precursor of glycosylphosphatidylinositol (GPI) anchors. Its azide would enable further modification to introduce other molecular tags by a biocompatible click reaction. Therefore, it can be a useful probe for metabolic engineering of cell surface GPI anchors and GPI-anchored proteins.

Engineering designer biologics in plant cells for oral treatment of inflammatory bowel disease (IBD)

Inflammatory bowel disease (IBD), including the two most common subtypes: Crohn’s disease (CD) and ulcerative colitis (UC), represents a group of intestinal disorders that cause prolonged inflammation of the digestive tract. The current treatment strategies, including the conventional anti‐inflammatory medications and the new biological drugs targeting the pro‐inflammatory cytokine tumor necrosis factor alpha (TNFα), have limited therapeutic efficacy and adverse drug reactions resulted from systemic administration. Colon‐targeted oral delivery of anti‐TNFα agents is highly desirable for the treatment of IBD, as it improves drugs’ efficacy while reducing systemic toxicity. Plant cell culture has emerged as a safe and cost‐effective bioproduction platform for therapeutic proteins. A unique feature of the plant cells is that they could serve not only as the “bio‐factory,” but also the oral delivery vehicle for recombinant biologics. Recent advances have demonstrated that plant cell walls, made primarily of cellulose microfibrils, can act as an excellent natural capsule for oral delivery of biologic drugs. This project aims to leverage two unique posttranslational modifications – “glycosyl‐phosphatidylinositol (GPI) anchor” and “plant‐specific hydroxyproline (Hyp)‐O‐glycosylation” – to strategically design and engineer novel anti‐TNFα biomolecules in plant cells to develop a new class of oral biologic drugs for the treatment of UC. The designer anti‐TNFα biomolecules consist of three functional domains: a N‐terminal single‐chain fragment variable (scFv) of an anti‐TNFα antibody, a proprietary Hyp‐O‐glycosylation module comprised of tandem repeats of the “Ser‐Pro” motif, or (SP)n (n= 5 to 30), and a C‐terminal GPI anchor. While the GPI anchor “displays” the expressed anti‐TNFα biomolecules at the plant cell surface to presumably create a high local concentration of the biologics, the (SP)n glycomodule stabilizes the protein from degradation during both the bioproduction and oral delivery processes. Designer anti‐TNFα biomolecules consisting of different sizes of the (SP)n glycomodule are investigated for their accumulations in tobacco BY‐2 cells, biological activity, and stability in a simulated gastric fluid, which determines the (SP)20 module as an optimal design for the biomolecules. The therapeutic effectiveness of the orally administrated designer anti‐TNFα biologic (optimal design) in mitigating the UC symptom is assessed in a dextran sulfate sodium (DSS)‐induced colitis mouse model. The immune‐modulatory effects of the anti‐TNFα biologics are determined by histopathological analysis and assay of the inflammatory markers. The research may develops a new platform to produce effective oral biologic drugs for the treatment of UC and other inflammatory diseases of colon.

Damaging novel mutations in PIGN cause developmental epileptic-dyskinetic encephalopathy: a case report

BackgroundMutations in PIGN, resulting in a glycosylphosphatidylinositol (GPI) anchor deficiency, typically leads to multiple congenital anomalies-hypotonia-seizures syndrome. However, the link between PIGN and epilepsy or paroxysmal non-kinesigenic dyskinesia (PNKD) is not well-described. This study reported a patient with PIGN mutation leading to developmental and epileptic encephalopathy and PNKD, to expand upon the genotype–phenotype correlation of PIGN.Case presentationDuring the first 10 days of life, a girl exhibited paroxysmal staring episodes with durations that ranged from several minutes to hours. These episodes occurred 2–5 times daily and always occurred during wakefulness. Ictal electroencephalography revealed no abnormalities, and PNKD was diagnosed. The patient also exhibited severely delayed psychomotor development and generalized seizures at the age of 4 months. Results of brain magnetic resonance imaging and metabolic screenings were normal, but trio-based whole-exome sequencing identified two novel compound heterozygous PIGN mutations (NM_176787; c.163C > T [p.R55 > X] and c.283C > T [p.R95W]). Flow cytometry analysis of the patient’s granulocytes revealed dramatically reduced expression of GPI-anchored proteins. This indicated that the mutations compromised GPI functions. The patient got seizure-free for 1 year, and her dyskinesia episodes reduced significantly (1–2 times/month) after treatment with levetiracetam (600 mg/day) and clonazepam (1.5 mg/day). No progress was observed with respect to psychomotor development; however, no craniofacial dysmorphic features, cleft lip/palate, brachytelephalangy with nail hypoplasia, and internal malformations have been observed until now (6 years of age).ConclusionThis is the first study to document developmental and epileptic encephalopathy with PNKD in a human with PIGN mutations. This report expanded our understanding of the genotype–phenotype correlation of PIGN, and PIGN may be considered a potentially relevant gene when investigating cases of epilepsy or PNKD.

The Leishmania donovani Ortholog of the Glycosylphosphatidylinositol Anchor Biosynthesis Cofactor PBN1 Is Essential for Host Infection.

ABSTRACTVisceral leishmaniasis is a deadly infectious disease caused by Leishmania donovani, a kinetoplastid parasite for which no licensed vaccine is available. To identify potential vaccine candidates, we systematically identified genes encoding putative cell surface and secreted proteins essential for parasite viability and host infection. We identified a protein encoded by LdBPK_061160 which, when ablated, resulted in a remarkable increase in parasite adhesion to tissue culture flasks. Here, we show that this phenotype is caused by the loss of glycosylphosphatidylinositol (GPI)-anchored surface molecules and that LdBPK_061160 encodes a noncatalytic component of the L. donovani GPI-mannosyltransferase I (GPI-MT I) complex. GPI-anchored surface molecules were rescued in the LdBPK_061160 mutant by the ectopic expression of both human genes PIG-X and PIG-M, but neither gene could complement the phenotype alone. From further sequence comparisons, we conclude that LdBPK_061160 is the functional orthologue of yeast PBN1 and mammalian PIG-X, which encode the noncatalytic subunits of their respective GPI-MT I complexes, and we assign LdBPK_061160 as LdPBN1. The LdPBN1 mutants could not establish a visceral infection in mice, a phenotype that was rescued by constitutive expression of LdPBN1. Although mice infected with the null mutant did not develop an infection, exposure to these parasites provided significant protection against subsequent infection with a virulent strain. In summary, we have identified the orthologue of the PBN1/PIG-X noncatalytic subunit of GPI-MT I in trypanosomatids, shown that it is essential for infection in a murine model of visceral leishmaniasis, and demonstrated that the LdPBN1 mutant shows promise for the development of an attenuated live vaccine.

Congenital diaphragmatic hernia and early lethality in PIGL-related disorder

We report on three male siblings who presented prenatally with a nearly identical combination of congenital anomalies and who died shortly after preterm birth. The first baby was a singleton pregnancy, and the other two babies were dichorionic diamniotic twins. Key features included: left-sided congenital diaphragmatic hernia, inferior vermian dysgenesis/hypoplasia, prenasal edema, cleft palate, micropenis/ambiguous genitalia (in 2 of 3 babies), bilateral renal pelvic dilatation (in twins, first baby showed slightly enlarged kidneys) and polyhydramnios (in 2 of 3). Whole genome sequencing performed on DNA from all three babies revealed homozygous missense PIGL gene variants: c.438C>A, p.(Phe146Leu). Both parents were heterozygous carriers of the variant. The reporting clinical laboratory classified the change as a variant of uncertain significance (VUS), and concluded “A genetic diagnosis of autosomal recessive CHIME syndrome is possible”. The PIGL gene has been reported to cause two different autosomal recessive conditions: CHIME syndrome and Mabry syndrome. CHIME (Zunich neuroectodermal syndrome) is characterized by ocular Colobomas, Heart defects, Ichthyosiform dermatosis, Mental retardation (intellectual disability), and Ear anomalies, including conductive hearing loss. Mabry [aka hyperphosphatasia mental retardation syndrome (HPMRS)] is characterized by severe developmental delay, moderate to severe intellectual disability, distinctive facial features, brachytelephalangy, increased serum levels of alkaline phosphatase (ALP), and recurrent seizures. Neonatal demise and lack of postmortem examination precluded assessment of some key features (including seizures, developmental delay, ALP levels, colobomas and deafness), but overlapping features observed included cleft palate, brain anomalies, genitourinary abnormalities and prenasal edema. Notably, diaphragmatic hernia is not a common feature of either condition, but is a cardinal feature of Fryns syndrome. The genetic etiology of Fryns syndrome has not been definitively established, although, much like CHIME and Mabry syndrome, can be caused by variants in glycosylphosphatidylinositol (GPI) anchor pathway genes. Our findings suggest further overlap between inherited GPI deficiencies, and possible expansion of the clinical phenotype of PIGL-related disorders to include prenatal presentations with congenital diaphragmatic hernia. Although reported as a VUS, we present phenotypic and familial segregation evidence that supports likely pathogenicity of the c.438C>A variant.

GPAA1 promotes the proliferation, invasion and migration of hepatocellular carcinoma cells by binding to RNA-binding protein SF3B4.

It has previously been reported that glycosylphosphatidylinositol anchor attachment 1 (GPAA1) is overexpressed in hepatocellular carcinoma (HCC); however, its role in regulating the development of HCC remains unknown. The present study aimed to examine the potential role of GPAA1 in HCC and to characterize the associated mechanism. The expression of GPAA1 was first examined using the Gene Expression Profiling Interactive Analysis 2 database, and was then determined using reverse transcription-quantitative PCR and western blotting. The effects of GPAA1 silencing on the proliferation, colony formation, migration and invasion of HuH-7 cells were measured using Cell Counting Kit-8, colony formation, wound healing and Transwell assays, respectively. The interaction between splicing factor (SF)3B4 and GPAA1 was predicted by starBase and confirmed using RNA immunoprecipitation. The results of the present study demonstrated that GPAA1 was upregulated in HCC cells, and silencing GPAA1 markedly inhibited the proliferation, migration and invasion of HCC cells, which was accompanied by reduced levels of MMP2 and MMP9. In addition, it was observed that SF3B4 could bind to GPAA1. Furthermore, to confirm whether SF3B4 binds to GPAA1 to modulate HCC cell behavior, GPAA1 was knocked down and SF3B4 was overexpressed. Overexpression of SF3B4 reversed the effects of GPAA1 knockdown on the proliferation, migration and invasion of HCC cells. In conclusion, SF3B4 may promote the proliferation, invasion and migration of HCC cells by binding to GPAA1. The present study provided novel insight into the pathogenesis of HCC.

Hedgehog pathway modulation by glypican 3-conjugated heparan sulfate.

Glypicans are a family of cell surface heparan sulfate proteoglycans that play critical roles in multiple cell signaling pathways. Glypicans consist of a globular core, an unstructured stalk modified with sulfated glycosaminoglycan chains, and a glycosylphosphatidylinositol anchor. Though these structural features are conserved, their individual contribution to glypican function remains obscure. Here, we investigate how glypican 3 (GPC3), which is mutated in Simpson-Golabi-Behmel tissue overgrowth syndrome, regulates Hedgehog signaling. We find that GPC3 is necessary for the Hedgehog response, surprisingly controlling a downstream signal transduction step. Purified GPC3 ectodomain rescues signaling when artificially recruited to the surface of GPC3-deficient cells but has dominant-negative activity when unattached. Strikingly, the purified stalk, modified with heparan sulfate but not chondroitin sulfate, is necessary and sufficient for activity. Our results demonstrate a novel function for GPC3-associated heparan sulfate and provide a framework for the functional dissection of glycosaminoglycans by in vivo biochemical complementation. This article has an associated First Person interview with the first author of the paper.

Glycosylphosphatidylinositol Anchor Biosynthesis Pathway-Related Protein GPI7 Is Required for the Vegetative Growth and Pathogenicity of Colletotrichum graminicola

Glycosylphosphatidylinositol (GPI) anchoring is a common post-translational modification in eukaryotic cells and has been demonstrated to have a wide range of biological functions, such as signal transduction, cellular adhesion, protein transport, immune response, and maintaining cell wall integrity. More than 25 proteins have been proven to participate in the GPI anchor synthesis pathway which occurs in the cytoplasmic and the luminal face of the ER membrane. However, the essential proteins of the GPI anchor synthesis pathway are still less characterized in maize pathogen Colletotrichum graminicola. In the present study, we analyzed the biological function of the GPI anchor synthesis pathway-related gene, CgGPI7, that encodes an ethanolamine phosphate transferase, which is localized in ER. The vegetative growth and conidia development of the ΔCgGPI7 mutant was significantly impaired in C. graminicola. and qRT-PCR results showed that the transcriptional level of CgGPI7 was specifically induced in the initial infection stage and that the pathogenicity of ΔCgGPI7 mutant was also significantly decreased compared with the wild type. Furthermore, the ΔCgGPI7 mutant displayed more sensitivity to cell wall stresses, suggesting that CgGPI7 may play a role in the cell wall integrity of C. graminicola. Cell wall synthesis-associated genes were also quantified in the ΔCgGPI7 mutant, and the results showed that chitin and β-1,3-glucans synthesis genes were significantly up-regulated in ΔCgGPI7 mutants. Our results suggested that CgGPI7 is required for vegetative growth and pathogenicity and might depend on the cell wall integrity of C. graminicola.

GPC2 Is a Potential Diagnostic, Immunological, and Prognostic Biomarker in Pan-Cancer.

BackgroundGlypican 2 (GPC2), a member of glypican (GPC) family genes, produces proteoglycan with a glycosylphosphatidylinositol anchor. It has shown its ascending significance in multiple cancers such as neuroblastoma, malignant brain tumor, and small-cell lung cancer. However, no systematic pan-cancer analysis has been conducted to explore its function in diagnosis, prognosis, and immunological prediction.MethodsBy comprehensive use of datasets from The Cancer Genome Atlas (TCGA), Cancer Cell Line Encyclopedia (CCLE), Genotype-Tissue Expression Project (GTEx), cBioPortal, Human Protein Atlas (HPA), UALCAN, StarBase, and Comparative Toxicogenomics Database (CTD), we adopted bioinformatics methods to excavate the potential carcinogenesis of GPC2, including dissecting the correlation between GPC2 and prognosis, gene mutation, immune cell infiltration, and DNA methylation of different tumors, and constructed the competing endogenous RNA (ceRNA) networks of GPC2 as well as explored the interaction of GPC2 with chemicals and genes.ResultsThe results indicated that GPC2 was highly expressed in most cancers, except in pancreatic adenocarcinoma, which presented at a quite low level. Furthermore, GPC2 showed the early diagnostic value in 16 kinds of tumors and was positively or negatively associated with the prognosis of different tumors. It also verified that GPC2 was a gene associated with most immune-infiltrating cells in pan-cancer, especially in thymoma. Moreover, the correlation with GPC2 expression varied depending on the type of immune-related genes. Additionally, GPC2 gene expression has a correlation with DNA methylation in 20 types of cancers.ConclusionThrough pan-cancer analysis, we discovered and verified that GPC2 might be useful in cancer detection for the first time. The expression level of GPC2 in a variety of tumors is significantly different from that of normal tissues. In addition, the performance of GPC2 in tumorigenesis and tumor immunity also confirms our conjecture. At the same time, it has high specificity and sensitivity in the detection of cancers. Therefore, GPC2 can be used as an auxiliary indicator for early tumor diagnosis and a prognostic marker for many types of tumors.

The function of glypicans in the mammalian embryo.

Glypicans are proteoglycans that are bound to the outer surface of the plasma membrane by a glycosylphosphatidylinositol anchor. The mammalian genome contains six members of the glypican family (GPC1 to GPC6). Although the degree of sequence homology within the family is rather low, the three-dimensional structure of these proteoglycans is highly conserved. Glypicans are predominantly expressed during embryonic development. Genetic and biochemical studies have shown that glypicans can stimulate or inhibit the signaling pathways triggered by Wnts, hedgehogs, fibroblast growth factors, and bone morphogenetic proteins. The study of mutant mouse strains demonstrated that glypicans have important functions in the developmental morphogenesis of various organs. In addition, a role of glypicans in synapsis formation has been established. Notably, glypican loss-of-function mutations are the cause of three human inherited syndromes. Recent analysis of glypican compound mutant mice has demonstrated that members of this protein family display redundant functions during embryonic development.

Tiki proteins are glycosylphosphatidylinositol-anchored proteases.

Wnt signalling pathways play pivotal roles in development, homeostasis and human diseases, and are tightly regulated. We previously identified Tiki as a novel family of Wnt inhibitory proteases. Tiki proteins were predicted as type I transmembrane proteins and can act in both Wnt-producing and Wnt-responsive cells. Here, we characterize Tiki proteins as glycosylphosphatidylinositol (GPI)-anchored proteases. TIKI1/2 proteins are enriched on the detergent-resistant membrane microdomains and can be released from the plasma membrane by GPI-specific glycerophosphodiesterases GDE3 and GDE6, but not by GDE2. The GPI anchor determines the cellular localization of Tiki proteins and their regulation by GDEs, but not their inhibitory activity on Wnt signalling. Our study uncovered novel characteristics and potential regulations of the Tiki family proteases.

Protein Lipidation Types: Current Strategies for Enrichment and Characterization.

Post-translational modifications regulate diverse activities of a colossal number of proteins. For example, various types of lipids can be covalently linked to proteins enzymatically or non-enzymatically. Protein lipidation is perhaps not as extensively studied as protein phosphorylation, ubiquitination, or glycosylation although it is no less significant than these modifications. Evidence suggests that proteins can be attached by at least seven types of lipids, including fatty acids, lipoic acids, isoprenoids, sterols, phospholipids, glycosylphosphatidylinositol anchors, and lipid-derived electrophiles. In this review, we summarize types of protein lipidation and methods used for their detection, with an emphasis on the conjugation of proteins with polyunsaturated fatty acids (PUFAs). We discuss possible reasons for the scarcity of reports on PUFA-modified proteins, limitations in current methodology, and potential approaches in detecting PUFA modifications.

Characterization of Arabidopsis Post-Glycosylphosphatidylinositol Attachment to Proteins Phospholipase 3 Like Genes.

Lipid remodeling of Glycosylphosphatidylinositol (GPI) anchors is required for their maturation and may influence the localization and function of GPI-anchored proteins (GPI-APs). Maturation of GPI-anchors is well characterized in animals and fungi but very little is known about this process in plants. In yeast, the GPI-lipid remodeling occurs entirely at the ER and is initiated by the remodeling enzyme Bst1p (Post-Glycosylphosphatidylinositol Attachment to Proteins inositol deacylase 1 -PGAP1- in mammals and Arabidopsis). Next, the remodeling enzyme Per1p (Post-Glycosylphosphatidylinositol Attachment to Proteins phospholipase 3 -PGAP3- in mammals) removes a short, unsaturated fatty acid of phosphatidylinositol (PI) that is replaced with a very long-chain saturated fatty acid or ceramide to complete lipid remodeling. In mammals, lipid remodeling starts at the ER and is completed at the Golgi apparatus. Studies of the Arabidopsis PGAP1 gene showed that the lipid remodeling of the GPI anchor is critical for the final localization of GPI-APs. Here we characterized loss-of-function mutants of Arabidopsis Per1/PGAP3 like genes (AtPGAP3A and AtPGAP3B). Our results suggest that PGAP3A function is required for the efficient transport of GPI-anchored proteins from the ER to the plasma membrane/cell wall. In addition, loss of function of PGAP3A increases susceptibility to salt and osmotic stresses that may be due to the altered localization of GPI-APs in this mutant. Furthermore, PGAP3B complements a yeast strain lacking PER1 gene suggesting that PGAP3B and Per1p are functional orthologs. Finally, subcellular localization studies suggest that PGAP3A and PGAP3B cycle between the ER and the Golgi apparatus.

Visualisation of experimentally determined and predicted protein N-glycosylation and predicted glycosylphosphatidylinositol anchor addition in Trypanosoma brucei.

Background: Trypanosoma brucei is a protozoan parasite and the etiological agent of human and animal African trypanosomiasis. The organism cycles between its mammalian host and tsetse vector. The host-dwelling bloodstream form of the parasite is covered with a monolayer of variant surface glycoprotein (VSG) that enables it to escape both the innate and adaptive immune systems. Within this coat reside lower-abundance surface glycoproteins that function as receptors and/or nutrient transporters. The glycosylation of the Trypanosoma brucei surface proteome is essential to evade the immune response and is mediated by three oligosaccharyltransferase genes; two of which, TbSTT3A and TbSTT3B, are expressed in the bloodstream form of the parasite. Methods: We processed a recent dataset of our laboratory to visualise putative glycosylation sites of the Trypanosoma brucei proteome. We provided a visualisation for the predictions of glycosylation carried by TbSTT3A and TbSTT3B, and we augmented the visualisation with predictions for Glycosylphosphatidylinositol anchoring sites, domains and topology of the Trypanosoma brucei proteome. Conclusions: We created a web service to explore the glycosylation sites of the Trypanosoma brucei oligosaccharyltransferases substrates, using data described in a recent publication of our laboratory. We also made a machine learning algorithm available as a web service, described in our recent publication, to distinguish between TbSTT3A and TbSTT3B substrates.

Visualisation of experimentally determined and predicted protein N-glycosylation and predicted glycosylphosphatidylinositol anchor addition in Trypanosoma brucei.

Background: Trypanosoma brucei is a protozoan parasite and the etiological agent of human and animal African trypanosomiasis. The organism cycles between its mammalian host and tsetse vector. The host-dwelling bloodstream form of the parasite is covered with a monolayer of variant surface glycoprotein (VSG) that enables it to escape both the innate and adaptive immune systems. Within this coat reside lower-abundance surface glycoproteins that function as receptors and/or nutrient transporters. The glycosylation of the Trypanosoma brucei surface proteome is essential to evade the immune response and is mediated by three oligosaccharyltransferase genes; two of which, TbSTT3A and TbSTT3B, are expressed in the bloodstream form of the parasite. Methods: We processed a recent dataset of our laboratory to visualise putative glycosylation sites of the Trypanosoma brucei proteome. We provided a visualisation for the predictions of glycosylation carried by TbSTT3A and TbSTT3B, and we augmented the visualisation with predictions for Glycosylphosphatidylinositol anchoring sites, domains and topology of the Trypanosoma brucei proteome. Conclusions: We created a web service to explore the glycosylation sites of the Trypanosoma brucei oligosaccharyltransferases substrates, using data described in a recent publication of our laboratory. We also made a machine learning algorithm available as a web service, described in our recent publication, to distinguish between TbSTT3A and TbSTT3B substrates.