Studies on the plasma membrane of normal and psoriatic keratinocytes. 4. Characterization of glycoconjugates

Abstract

A substantial proportion (20-50%) of radioactive sugar incorporated into glycoconjugates by normal human keratinocytes was soluble in chloroform-methanol; using (14C)-galactose as precursor about half of this fraction was neutral lipid. The incorporation of labelled sugars into the lipid fraction was consistently increased in keratinocytes derived from psoriatic lesions. The abnormality in fucose metabolism which we reported previously has been confirmed. In particular we have shown that the molecular weight of fucosylated glycopeptides appears to be abnormally high in the untreated psoriatic lesion, possibly reflecting an increased degree of branching. In psoriatic uninvolved epidermis and in treated psoriatic lesions the situation is reversed, the molecular weight being significantly lower than normal.

Studies on the plasma membrane of normal and psoriatic keratinocytes. 5. Lectin binding

“…Thus we must assume either structural changes in the oligosaccharide moieties in particular glycoproteins or an alteration in the relative amounts ofthe different types of glycoprotein. The marked increase in the association constant of UEA (fucose-binding) is noteworthy, and may be correlated with the changes in molecular weight distribution of total membrane glycopeptides found after labelling with fucose (Roelfzema et al, 1981b).…”

“…A marked increase in the affinity of the cell surface for Ulex europus agglutinin (fucose-specific) confirms our previous reports of structural alterations in fucose-containing oligosaccharides in psoriasis.In previous papers in this series we have reported profound abnormalities in the metabolism of certain sugars by psoriatic keratinocytes. Disturbances include an increased rate of entry of labelled sugars into the cell and of their incorporation into glycoconjugates (Roelfzema et al, 1981 a) and changes in the structure of the oligosaccharide fragments remaining after proteolytic digestion of cellular glycoprotein (Roelfzema et al, 1981b). Such findings are compatible with the altered cell cycle kinetics of the psoriatic lesion, since the surface receptors which couple the external milieu to the intracellular regulators are mostly glycoprotein in nature (Kahn, 1976).A direct analysis of the carbohydrate content of glycoconjugates located on the cell surface would therefore be very useful in extending these findings.…”

“…In previous papers in this series we have reported profound abnormalities in the metabolism of certain sugars by psoriatic keratinocytes. Disturbances include an increased rate of entry of labelled sugars into the cell and of their incorporation into glycoconjugates (Roelfzema et al, 1981 a) and changes in the structure of the oligosaccharide fragments remaining after proteolytic digestion of cellular glycoprotein (Roelfzema et al, 1981b). Such findings are compatible with the altered cell cycle kinetics of the psoriatic lesion, since the surface receptors which couple the external milieu to the intracellular regulators are mostly glycoprotein in nature (Kahn, 1976).…”

Studies in Immunodermatology

“…Roelfzema et al [19] have shown the incor poration of labelled sugars into glycoproteins, glycolipids and proteoglycans by keratinocytes.…”

“…These lipid bilayers include very little of phospholipids thought to be essential for the arrange ments of lipids into bilayers. However, it is thought that sphingolipids and sterols help in the maintenance of bilayer structure [9,10,19] and that these lipids and glycoconjugates may be the macromolecules which mask the SCAg.…”