Host-cell-specific glycosylation of HIV-2 envelope glycoprotein

Neutral complex-type N-glycans of the envelope glycoprotein 120 of HIV-2, propagated in different host cells, display cell-type specific variations. In order to identify typical structural elements, glycans were analysed by gel filtration, by enzymic sequencing and, in part, by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The characteristic substituents of di- tri- and tetraantennary carbohydrate units thus observed include N-acetyllactosamine repeats, bisecting N-acetylglucosamine and fucose linked to the chitobiose core as well as to N-acetyllactosamine antennae. Each glycoprotein preparation displayed a characteristic set of glycoforms. This revised version was published online in November 2006 with corrections to the Cover Date.     

The molecular mechanism of neural induction: neural differentiation of Triturus ectoderm exposed to Hepes buffer

Summary Ectoderm was isolated from early gastrula stages of Triturus alpestris and cultured in salt solution buffered with either bicarbonate or Hepes as the principal buffer substance. When bicarbonate was the principal buffer substance or when bicarbonate was omitted, the isolated ectoderm formed atypical epidermis. When Hepes was added as a buffer substance, neural tissue was formed in a high percentage of cases. The differentiation of neural tissue depends on the pH of the Hepes buffer. Hepes in the protonated form, which prevails at lower pH, seems to evoke neural differentiation at a much higher rate. Hepes could either enhance the NA⁺/H⁺ antiport system or it could directly bind to plasma membrane constituents. In both cases conformational changes in the plasma membrane could generate signals which finally lead to neural differentiation.     

Die Induktionsfähigkeit des Hypophysenvorderlappens vom Rind in Gastrulen von Triton alpestris

Ohne ZusammenfassungHerrn Prof. Dr.Walter Schoeller zum 75. Geburtstag gewidmet.Ausgeführt mit Unterstützung der Deutschen Forschungsgemeinschaft.     

Strategies for analysis of glycoprotein glycosylation

Glycoproteins are known to exhibit multiple biological functions. In order to assign distinct functional properties to defined structural features, detailed information on the respective carbohydrate moieties is required. Chemical and biochemical analyses, however, are often impeded by the small amounts of sample available and the vast structural heterogeneity of these glycans, thus necessitating highly sensitive and efficient methods for detection, separation and structural investigation. The aim of this article is to briefly review suitable strategies for characterization of glycosylation at the levels of intact proteins, glycopeptides and free oligosaccharides. Furthermore, methods commonly used for isolation, fractionation and carbohydrate structure analysis of liberated glycoprotein glycans are discussed in the context of potential applications in glycoproteomics.     

Free zinc inhibits transport of vitamin C in differentiated HL-60 cells during respiratory burst

Zinc is an essential trace element for the immune system. It is known to be essential for highly proliferating cells, especially for cells of the immune system. However, zinc and other divalent cations are known to inhibit the human neutrophilic NADPH oxidase. Differentiated HL-60 cells were found to accumulate large quantities of vitamin C (ascorbate) after activation of the NADPH oxidase by phorbol esters (PMA). This increase in vitamin C transport is due to the generation of superoxide and subsequent oxidation of ascorbate to dehydroascorbate (DHA) which is preferentially taken up by the cells. We found that zinc reversibly inhibits both PMA-stimulated ascorbate uptake and superoxide generation with a half-maximal effect at 20 microM of free zinc ions. Higher residual extracellular ascorbate concentrations were measured with increasing zinc concentrations, indicating that less ascorbate was oxidized and taken up by the cells. When the fluorescent dye diSC3(5) was used to monitor shifts in membrane potential, we found that depolarization with PMA was prolonged after preincubation of the cells with zinc. Suppression of the respiratory burst as well as inhibition of the uptake of the antioxidant vitamin C may disturb the balance between oxidative damage of invading particles and antioxidant protection in activated neutrophils.