Protein glycosylation is a general post-translational modification pathway that controls various biological functions including protein trafficking, cell adhesion, and protein-ligand interaction [...].
Key Words: N-glycan, congenital disorders of glycosylation (CDG), steroid 5alpha-reductase 3 (SRD5A3), dolicholThe process of N-glycosylation mainly consists of three steps: First an oligosaccharide precursor (Glc 3 Man 9 GlcNAc 2 ) is assembled on the lipid carrier dolichol-phosphate (Dol-P) on the endoplasmic reticulum (ER) membrane.Second, this glycan block is transferred to asparagine residues in the consensus sequence N-X-S/T (where X can be any amino acid except proline) of nascent glycoproteins by oligosaccharyl transferase.Third, the N-glycan is modified by subsequent trimming and elongation reactions beginning in the ER and ending in the Golgi apparatus.In humans, disruptions in N-glycosylation lead to congenital disorders of glycosylation (CDGs), which can be diagnosed simply and reliably by a screening test of the N-glycosylation status of a serum protein, transferrin.Defects in the maturation and transfer of the glycan precursor, located in the ER, have been grouped as CDG type I, and disorders affecting the subsequent N-glycan processing steps (or affecting O-glycosylation) are grouped as CDG type II.Although these diseases show extremely wide symptoms and severity, several cases have been reported with primary neurological involvement including cerebellar ataxia, suggesting that cerebellar disease may be a sensitive measure of defective N-glycosylation.The authors identified a large consanguineous Emirati family of Baluchi (Southern Iran) origin (CVH-385) with a new autosomal recessive syndrome.All affected children manifested ocular colobomas, ichthyosis, heart defect, developmental delay, and brain malformations including cerebellar vermis hypoplasia.By performing a genomewide linkage analysis, they mapped the disease locus on chromosome 4q12 containing 42 genes, which were then screened for mutation with bidirectional sequencing.The steroid 5α-reductase 3 (SRD5A3) gene turned out to have a molecular rearrangement with a homozygous 3-bp deletion and a 10-bp insertion resulting in a predicted stop codon at amino acid 96.The phenotypic similarity with several CDGs prompted a test for the N-glycosylation status of transferrin using mass spectrometry.CVH-385 showed a very clear defect with approximately 45% of monoglycosylated transferrin, suggesting that the SRD5A3 mutation results in a CDG type I.To begin to understand the biochemical function of SRD5A3, the authors examined a homolog in yeast.A yeast
Abstract— To obtain information on the ecotoxicological properties of liquid‐crystal (LC) compounds, the aquatic toxicity of selected LCs was investigated. Therefore, ten single LCs and one LC mixture were tested for their toxicity to the two standard organisms, daphnia (immobilization) and algae (growth inhibition). Water solubilities and detection limits were determined in the test media. Up to the limit of water solubility, the LCs as well as the LC mixture did not cause any adverse effects to the tested organisms.
The extracellular domain of Notch contains epidermal growth factor (EGF) repeats that are extensively modified with different O-linked glycans. O-Fucosylation is essential for receptor function, and elongation with N-acetylglucosamine, catalyzed by members of the Fringe family, modulates Notch activity. Only recently, genes encoding enzymes involved in the O-glucosylation pathway have been cloned. In the Drosophila mutant rumi, characterized by a mutation in the protein O-glucosyltransferase, Notch signaling is impaired in a temperature-dependent manner, and a mouse knock-out leads to embryonic lethality. We have previously identified two human genes, GXYLT1 and GXYLT2, encoding glucoside xylosyltransferases responsible for the transfer of xylose to O-linked glucose. The identity of the enzyme further elongating the glycan to generate the final trisaccharide xylose-xylose-glucose, however, remained unknown. Here, we describe that the human gene C3ORF21 encodes a UDP-xylose:α-xyloside α1,3-xylosyltransferase, acting on xylose-α1,3-glucoseβ1-containing acceptor structures. We have, therefore, renamed it XXYLT1 (xyloside xylosyltransferase 1). XXYLT1 cannot act on a synthetic acceptor containing an α-linked xylose alone, but requires the presence of the underlying glucose. Activity on Notch EGF repeats was proven by in vitro xylosylation of a mouse Notch1 fragment recombinantly produced in Sf9 insect cells, a bacterially expressed EGF repeat from mouse Notch2 modified in vitro by Rumi and Gxylt2 and in vivo by co-expression of the enzyme with the Notch1 fragment. The enzyme was shown to be a typical type II membrane-bound glycosyltransferase localized in the endoplasmic reticulum.
Eight of 15 human ovarian carcinoma cell lines were shown to express high levels of hyaluronan (HA) on their surfaces. The role of cell surface HA in its adhesion to mesothelial cells, which is potentially involved in peritoneal dissemination, was evaluated. Three human ovarian carcinoma cell lines, ES-2, MH, and KF cells, were repeatedly sorted into variant cell lines with high levels of cell surface HA (ES-2/HA+7, MH/HA+7, and KF/HA+7) and with low cell surface HA (ES-2/HA-7, MH/HA-7, and KF/HA-7). The ability of these cells to adhere to peritoneal mesothelial cells was compared. ES-2/HA+7, MH/HA+7, and KF/HA+7 cells were less adherent to mesothelial cells than the ES-2/HA-7, MH/HA-7, and KF/HA-7 cells. On ovarian carcinoma cells, high cell surface HA levels seem to inversely correlate with their capacity to adhere and disseminate to the peritoneum. Considering that peritoneum implantation is the primary ovarian cancer complication, HA cell surface expression may be considered a property associated with a less aggressive phenotype, which is contrary to the general perception that HA expression is associated with malignant progression.
The atypical cadherin Fat acts as a receptor for a signaling pathway that regulates growth, gene expression, and planar cell polarity. Genetic studies in Drosophila identified the four-jointed gene as a regulator of Fat signaling. We show that four-jointed encodes a protein kinase that phosphorylates serine or threonine residues within extracellular cadherin domains of Fat and its transmembrane ligand, Dachsous. Four-jointed functions in the Golgi and is the first molecularly defined kinase that phosphorylates protein domains destined to be extracellular. An acidic sequence motif (Asp-Asn-Glu) within Four-jointed was essential for its kinase activity in vitro and for its biological activity in vivo. Our results indicate that Four-jointed regulates Fat signaling by phosphorylating cadherin domains of Fat and Dachsous as they transit through the Golgi.
