Immunogenic properties of mannose-containing ceramide disaccharide and immunochemical detection of its hapten in the two kinds of crustacean, Euphausia superba and Macrobrachium nipponense.

Antiserum against Man beta 1-4Glc beta 1-1Ceramide (MIOse2Cer), a mannolipid isolated from spermatozoa of the fresh-water bivalve, Hyriopsis schlegellii, has been elicited in rabbits by repeated injection of a mixture of hapten-bovine serum albumin (1:1, mg/ml) with Freund's adjuvant. The specificity of the affinity-purified antibody (immunoglobulin G type) obtained from the serum was examined, using other glycosphingolipids and glyco-proteins structurally related to MIOse2Cer, by means of ELISA and TLC-immunostaining. The purified antibody was highly specific to MIOse2Cer and lacked reactivity with other glycolipids and glycoproteins including glucosylceramide, lactosylceramide, dimannosylglucosylceramide (MIOse3Cer), glucosaminylmannosylglucosylceramide (ArOse3Cer), thyroglobulin and alpha 1-acid glycoprotein. The antibody was found to bind, although less efficiently, to certain other compounds containing the group Man beta 1-4Glc and/or Man beta 1-4GlcNAc at their termini, such as MIOse2-sphingosine and Man beta 1-4GlcNAc beta 1-p-aminobenzoic acid ethylester derivatives. The present antibody was applied to the detection of the natural hapten in crustacean glycolipids. The purified antibody reacted with a neutral glycosphingolipid present in the two kinds of crustacean, Euphausia superba (antarctic krill) and Macrobrachium nipponense (fresh-water shrimp) as shown by TLC-immunostaining. The crustacean glycolipid antigen was isolated and characterized to be the Man beta 1-4Glc-Cer. This is the first report on the presence of a mannose-containing glycosphingolipid in the crustacean.     

Differing cell surface distribution of human leukocyte antigen-DR molecules on epidermal Langerhans cells and eccrine duct cells.

Scanning electron microscopy (SEM) with immunogold labeling was employed to observe the undersurface of the human epidermis after it was split from dermal connective tissue, in an attempt to localize the molecules actually expressed on cell/tissue surfaces. We found that human leukocyte antigen-DR (HLA-DR) molecules were expressed on the surfaces of eccrine duct cells as well as those of epidermal Langerhans cells (LC) in normal skin. HLA-DR molecules, visualized by the deposition of gold particles, were distributed evenly on the LC surface but were present only along the interdigitating borders of the individual duct cells, thus producing a meshwork pattern on the duct surface. Transmission electron microscopy confirmed that the gold particles labeling cell surface HLA-DR molecules were seen only on the portions of duct cell membranes the interdigitated with neighboring duct cells. These findings suggest that the function of HLA-DR molecules may vary with their location and distribution. On the LC surface, the evenly distributed molecules seem to be well suited for promoting "accessory cell" functions. On duct cell surfaces, the HLA-DR molecules present along the intercellular spaces may be involved in trapping various peptide antigens that pass into the sweat gland filtrate and then are reabsorbed by the excretory duct, since these molecules have a highly permissive capacity for binding various peptides.     

Solubilization of human placental tumor necrosis factor receptors as a complex with a guanine nucleotide-binding protein.

Human placental membranes exhibited high-affinity receptors for tumor necrosis factor (TNF) (Kd = 5.6 x 10(-10) M) with a density of 1.2-1.7 x 10(10) sites/mg protein. The receptors were solubilized from these membranes with 1% Nonidet P-40, and the solubilized receptor was adsorbed to Con A-Sepharose and wheat germ agglutinin agarose columns, indicating that the TNF receptor derived from human placenta contains carbohydrate chains recognized by these lectins. TNF binding activity was eluted from a column of Sephacryl S-300 as a single peak of Mr 300 kDa. The solubilized receptor was further purified by TNF-Sepharose prepared by coupling of TNF to tresyl-activated Sepharose 4B. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the purified sample resolved five major bands of Mr 90, 78, 41, 35, and 11 kDa, suggesting that these polypeptides constitute a multimeric complex with a molecular mass of 300 kDa, as observed in gel filtration study. Furthermore, the TNF-Sepharose-bound fraction demonstrated GTP gamma S binding and GTPase activity. Immunoblot analysis showed that the 41- and 35-kDa polypeptides were recognized by antisera against alpha subunits and beta subunit of GTP-binding proteins, respectively. These results suggest that the native TNF receptor couples to a guanine nucleotide-binding protein to form a large complex structure in human placental membranes.     

Identification of a novel amino acid, o-bromo-L-phenylalanine, in egg-associated peptides that activate spermatozoa

Eight sperm-activating peptides containing a novel amino acid were isolated from the egg jelly of the sea urchin Tripneustes gratilla. Accurate mass measurement of the peptide in FAB mass spectrometry showed that the mass of the novel amino acid residue was 224.978. On the basis of the isotopic ion distribution and the degree of unsaturation, the mass value indicated that the elemental composition of the amino acid residue was C9H8O1N1Br1, suggesting that the novel amino acid was bromophenylalanine. Proton NMR spectroscopy, amino acid analysis, and RP-HPLC with three synthetic isomers of bromophenylalanine demonstrated that o-bromophenylalanine was the novel amino acid. Derivatization of the amino acid with Marfey's reagent, (1-fluoro-2,4-dinitrophen-5-yl)-L-alanine amide (FDAA), further indicated that the amino acid was the L-isomer. In other sperm-activating peptides isolated from the egg jelly of the sea urchin, both m- and p-bromophenylalanines were discovered. The presence of m-bromophenylalanine has not been previously reported in natural products, while p-bromophenylalanine is found in theonellamide F, an antifungal bicyclic peptide from a marine sponge.     

The influence of glycosylation on the fate of renin expressed in Xenopus oocytes

It has been recently reported that, in Xenopus oocytes injected with the mRNA for human renin, this secretory renal glycoprotein acquires phosphomannosyl residues on its asparagine-linked oligosaccharide chains, remains intracellular and undergoes a proteolytic cleavage which removes the prosegment. To understand the influence of glycosylation on the fate of renin in Xenopus oocytes and whether it is specific for human renin, we have expressed human renin and mouse Ren1 renin, which are glycosylated at two and three selected asparagine residues, respectively, and mouse Ren2 renin, which is not glycosylated, in Xenopus oocytes. The majority of human and Ren1 renins remained intracellular and underwent proteolytic cleavage, whereas mouse Ren2 renin was secreted efficiently. When human and Ren1 renins were expressed in oocytes treated with tunicamycin, both were secreted efficiently. A mutant of human renin, which had amino-acid substitutions at both glycosylation sites, was also secreted efficiently, whereas that mutated at one of the two sites was not. These results indicate that the majority of all of the glycosylated renin molecules remain intracellular and undergo proteolytic cleavage, probably due to the acquisition of phosphomannosyl residues, and the human renin remains intracellular if it is only glycosylated at one of the two sites.     

Inhibition of epidermal growth factor-induced DNA synthesis by tyrosine kinase inhibitors

We prepared methyl 2,5-dihydroxycinnamate as a stable analogue of erbstatin, a tyrosine kinase inhibitor. This analogue was about 4 times more stable than erbstatin in calf serum. It inhibited epidermal growth factor receptor-associated tyrosine kinase in vitro with an IC₅₀ of 0.15 μg/ml. It also inhibited in situ autophosphorylation of epidermal growth factor receptor in A431 cells. Methyl 2,5-dihydroxycinnamate was shown to delay the S-phase induction by epidermal growth factor in quiescent normal rat kidney cells, without affecting the total amount ofDNA synthesis. The effect of erbstatin on S-phase induction was smaller, possibly because of its shorter life time.     

Some common properties of lectins from marine algae

Twelve kinds of lectins isolated from four species of marine algae, Boodlea coacta (Chlorophyta) and Hypnea japonica, Carpopeltis flabellata and Solieria robusta (Rhodophyta), were compared for their chemical and biological properties. These lectins were proteins or glycoproteins, similar to terrestrial plant lectins. However, unlike most terrestrial plant lectins, they had a small molecular size (4,200 to 25,000 daltons), were mostly monomeric, and had no affinity for monosaccharides. They strongly agglutinated trypsin-treated rabbit erythrocytes, and their activities commonly were inhibited by glycoproteins bearing N-glycans. From hemagglutination-inhibition tests with various glycoproteins and related compounds, it was found that B. coacta lectins recognize high-mannose N-glycans; H. japonica lectins complex N-glycans, and C. flabellata and S. robusta lectins recognize both types of N-glycans.