88 research outputs found
Golgi targeting of Drosophila melanogaster Ī²4GalNAcTB requires a DHHC protein familyārelated protein as a pilot
Drosophila melanogaster Ī²4GalNAcTB mutant flies revealed that this particular N-acetylgalactosaminyltransferase is predominant in the formation of lacdiNAc (GalNAcĪ²1,4GlcNAc)-modified glycolipids, but enzymatic activity could not be confirmed for the cloned enzyme. Using a heterologous expression cloning approach, we isolated Ī²4GalNAcTB together with Ī²4GalNAcTB pilot (GABPI), a multimembrane-spanning protein related to Asp-His-His-Cys (DHHC) proteins but lacking the DHHC consensus sequence. In the absence of GABPI, inactive Ī²4GalNAcTB is trapped in the endoplasmic reticulum (ER). Coexpression of Ī²4GalNAcTB and GABPI generates the active enzyme that is localized together with GABPI in the Golgi. GABPI associates with Ī²4GalNAcTB and, when expressed with an ER retention signal, holds active Ī²4GalNAcTB in the ER. Importantly, treatment of isolated membrane vesicles with Triton X-100 disturbs Ī²4GalNAcTB activity. This phenomenon occurs with multimembrane-spanning glycosyltransferases but is normally not a property of glycosyltransferases with one membrane anchor. In summary, our data provide evidence that GABPI is required for ER export and activity of Ī²4GalNAcTB
Genetic Interactions Between Drosophila sialyltransferase and Ī²1,4-N-acetylgalactosaminyltransferase-A Genes Indicate Their Involvement in the Same Pathway
Sialylated glycans play a prominent role in the Drosophila nervous system where they are involved in the regulation of neural transmission. However, the functional pathway of sialylation in invertebrates, including Drosophila, remains largely unknown. Here we used a combination of genetic and behavioral approaches to shed light on the Drosophila sialylation pathway. We examined genetic interactions between Drosophila sialyltransferase (DSiaT) and Ī²1,4-N-acetylgalactosaminyltransferase (Ī²4GalNAcT) genes. Our results indicated that Ī²4GalNAcTA and DSiaT cooperate within the same functional pathway that regulates neural transmission. We found that Ī²4GalNAcTA is epistatic to DSiaT. Our data suggest an intriguing possibility that Ī²4GalNAcTA may participate in the biosynthesis of sialylated glycans
Role of the complement in experimental sepsis
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142122/1/jlb0467.pd
C5aR and C5L2 act in concert to balance immunometabolism in adipose tissue
Recent studies suggested that the immunometabolic receptors; C5aR and C5L2, constitutively self-associate into homo-/heterodimers and that acylation stimulating protein (ASP/C3adesArg) or C5a treatment of adipocytes increased their colocalization. The present study evaluates the C5aR contribution in adipocytes to the metabolic and immune responses elicited by ligand stimulation.The effects of C5a, ASP, and insulin on cytokine production, triglyceride synthesis (TGS), and key signaling pathways were evaluated in isolated primary adipocytes and cultured 3T3-L1 differentiated adipocytes. In addition, mRNA expression of IRS1 and PGC1Ī± was compared in adipose tissue samples from WT vs. C5aRKO mice.Both C5a and ASP directly increased MCP-1 (238. Ā±. 4%;
Calcitonin receptor N-glycosylation enhances peptide hormone affinity by controlling receptor dynamics
The class B G protein-coupled receptor (GPCR) calcitonin receptor (CTR) is a drug target for osteoporosis and diabetes. N-glycosylation of asparagine 130 in its extracellular domain (ECD) enhances calcitonin hormone affinity with the proximal GlcNAc residue mediating this effect through an unknown mechanism. Here, we present two crystal structures of salmon calcitonin-bound, GlcNAc-bearing CTR ECD at 1.78 and 2.85 Ć
resolutions and analyze the mechanism of the glycan effect. The N130 GlcNAc does not contact the hormone. Surprisingly, the structures are nearly identical to a structure of hormone-bound, N-glycan-free ECD, which suggested that the GlcNAc might affect CTR dynamics not observed in the static crystallographic snapshots. Hydrogen-deuterium exchange mass spectrometry and molecular dynamics simulations revealed that glycosylation stabilized a Ī²-sheet adjacent to the N130 GlcNAc and the N-terminal Ī±-helix near the peptide-binding site, while increasing flexibility of the peptide-binding site turret loop. These changes due to N-glycosylation increased the ligand on-rate and decreased its off rate. The glycan effect extended to RAMP-CTR amylin receptor complexes and was also conserved in the related CGRP receptor. These results reveal that N-glycosylation can modulate GPCR function by altering receptor dynamics
Anticoagulants impact on innate immune responses and bacterial survival in whole blood models of Neisseria meningitidis infection
Neisseria meningitidis (meningococcus) causes invasive diseases such as meningitis or septicaemia. Ex vivo infection of human whole blood is a valuable tool to study meningococcal virulence factors and the host innate immune responses. In order to consider effects of cellular mediators, the coagulation cascade must be inhibited to avoid clotting. There is considerable variation in the anticoagulants used among studies of N. meningitidis whole blood infections, featuring citrate, heparin or derivatives of hirudin, a polypeptide from leech saliva. Here, we compare the influence of these three different anticoagulants, and additionally Mg/EGTA, on host innate immune responses as well as on viability of N. meningitidis strains isolated from healthy carriers and disease cases, reflecting different sequence types and capsule phenotypes. We found that the anticoagulants significantly impact on cellular responses and, strain-dependently, also on bacterial survival. Hirudin does not inhibit complement and is therefore superior over the other anticoagulants; indeed hirudin-plasma most closely reflects the characteristics of serum during N. meningitidis infection. We further demonstrate the impact of heparin on complement activation on N. meningitidis and its consequences on meningococcal survival in immune sera, which appears to be independent of the heparin binding antigens Opc and NHBA
Ligand specificity of the anaphylatoxin C5L2 receptor and its regulation on myeloid and epithelial cell lines
During complement activation the pro-inflammatory anaphylatoxins C3a and C5a are generated, which interact with the C3a receptor and C5a receptor (CD88), respectively. C5a and its degradation product C5a-des-Arg(74) also bind to the C5a receptor-like 2 (C5L2). C3a and C3a-des-Arg(77), also called acylation-stimulating protein, augment triglyceride synthesis and glucose uptake in adipocytes and skin fibroblasts. Based on data obtained using transfected HEK293 and RBL cells, C5L2 is additionally proposed as a functional receptor for C3a and C3a-des-Arg(77). Here we use (125)I-ligand binding assays and flow cytometry with fluorescently labeled ligands to demonstrate that neither C3a nor C3a-des-Arg(77) binds to C5L2. C5L2 expression and its regulation are investigated on various cell lines by a novel C5L2-restricted binding assay and quantitative real time PCR. Dibutyryl cAMP and interferon-gamma induce up-regulation of this receptor on myeloblastic cell lines (U937 and HL-60), whereas tumor necrosis factor-alpha (TNF-alpha) has no effect. In contrast, epithelial HeLa cells are found to constitutively express C5L2 but not the C5a receptor. In HeLa cells, interferon-gamma and TNF-alpha drastically reduce C5L2 expression. No C5a-dependent Ca(2+) signaling is observed even in these cells endogenously expressing C5L2. Taken together, C5L2 is not a receptor for C3a or C3a-des-Arg(77). Thus, this receptor is unlikely to be directly involved in lipid metabolism. Instead, the identification of stimuli modifying C5L2 expression indicates that C5L2 is a highly regulated scavenger receptor for C5a and C5a-des-Arg(74)
A novel protocol allowing oral delivery of a protein complement inhibitor that subsequently targets to inflamed colon mucosa and ameliorates murine colitis
A homopolymeric adenosine tract in the promoter region of nspA influences factor H-mediated serum resistance in Neisseria meningitidis
Although usually asymptomatically colonizing the human nasopharynx, the Gram-negative bacterium Neisseria meningitidis (meningococcus) can spread to the blood stream and cause invasive disease. For survival in blood, N. meningitidis evades the complement system by expression of a polysaccharide capsule and surface proteins sequestering the complement regulator factor H (fH). Meningococcal strains belonging to the sequence type (ST-) 41/44 clonal complex (cc41/44) cause a major proportion of serogroup B meningococcal disease worldwide, but they are also common in asymptomatic carriers. Proteome analysis comparing cc41/44 isolates from invasive disease versus carriage revealed differential expression levels of the outer membrane protein NspA, which binds fH. Deletion of nspA reduced serum resistance and NspA expression correlated with fH sequestration. Expression levels of NspA depended on the length of a homopolymeric tract in the nspA promoter: A 5-adenosine tract dictated low NspA expression, whereas a 6-adenosine motif guided high NspA expression. Screening German cc41/44 strain collections revealed the 6-adenosine motif in 39% of disease isolates, but only in 3.4% of carriage isolates. Thus, high NspA expression is associated with disease, but not strictly required. The 6-adenosine nspA promoter is most common to the cc41/44, but is also found in other hypervirulent clonal complexes
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