Lipid-linked structure

The discovery that phospholipase C could release alkahne phosphatase from lipid-linked structures on cellular surfaces (39) led to the identification of the glycophosphatidylinositol (GPI) membrane component (40). GPI structures are a synthetic tour de force of nature, combining lipids, carbohydrates, and proteins into a single macromolecule. Certain proteins require GPI anchoring to be functional for example, Ly-6A/E-mediated T-cell activation is critically dependent on its GPI anchor (41), and folate uptake functions efficiently only when its receptors are GPI anchored (42). 

Glycolipid 3-ce-mannosyltransferase [EC 2.4.1.132], also known as mannosyltransferase II, catalyzes the transfer of an ce-D-mannosyl residue from GDP-mannose into a lipid-linked oligosaccharide, forming an o -l,3-D-manno-syl-D-mannose linkage. The 1,3-linked mannosyl residue in the mammalian lipid-linked oligosaccharide of the structure Glc3Man9GlcNAc2 is produced by this enzyme. 

Fig. 16 Normalized transfection activity as a function of the hydrocarbon chain length (total number of carbon atoms) for the cationic lipids with structures given in the insets cationic phosphatidylcholines with saturated (a) and unsaturated (e, f) chains [46] hydroxyethyl quaternary ammonium lipids [35] (b) 1,4-dihydropyridine lipids [55] (c) carbamate-linked lipids [45] (d) pyridinium-based lipids with cis- (g) and /ra/u-unsaturated (h) chains [57]...

Abnormalities in lipid lamellar structure or corneodesmolysis are apparent in scaling disorders like X-linked Ichthyosis, atopic dry skin, or in winter xerosis.2,10 Susceptibility to dry skin also shows a tendency to increase with age.3 Exposure to dry environment or extreme shifts in external humidity produces important alterations in underlying skin. Dry environment stimulates epidermal hyperplasia and early markers of inflammation. Shift in external humidity induces a profound defect in... 

In addition to the variations of the GT-A and GT-B fold described above for sialyltransferases (7, 8) and fucosyltrans-ferases (17), a distinct GT-C fold family has been predicted for GTs that use lipid linked donors. The crystal structures of the GT domain of the peptidoglycan glycosyltransferase from Staphylococcus aureus (18) (Fig. 3f) and Aquifex aeolicus, (26) show structural similarity to the bacteriophage k-lysozyme. These novel structures demonstrate the possibility of additional folds. 

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