Glycosylphosphatidylinositol

Ferguson, MAJ (2000) Glycosylphosphatidylinositol biosynthesis validated as a drug target for African sleeping sickness. Proc Natl Acad Sci USA 97 10673-10675... 

The major classes of glycoproteins are O-linked (involving an OH of serine or threonine), N-linked (involving the N of the amide group of asparagine), and glycosylphosphatidylinositol (GPi)-linked. 

Much of the plasma membrane cholesterol is removed by incubating cells with P-methylcyclodextrin for several hours. Cells remain viable after this treatment but the raft fraction is reduced and it is inferred that the depleted proteins are normally associated with cholesterol-dependent lipid rafts. Some, but not all, glycosylphosphatidylinositol (GPI)-anchored proteins are recovered in the fractions defined by this procedure. 

A bacterial phosphatidylinositol specific phospholipase C (PI-PLC) had been available for many years before it was demonstrated to strip a number of membrane-bound proteins from eukaryotic cell surfaces [1], Such proteins are anchored by a PI moiety in which the 6 position of inositol is glycosidically linked to glucosamine, which in turn is bonded to a polymannan backbone (Fig. 3-10). The polysaccharide chain is joined to the carboxyl terminal of the anchored protein via amide linkage to ethanolamine phosphate. The presence of a free NH2 group in the glucosamine residue makes the structure labile to nitrous acid. Bacterial PI-PLC hydrolyzes the bond between DAG and phosphati-dylinositols, releasing the water-soluble protein polysac charide-inositol phosphate moiety. These proteins are tethered by glycosylphosphatidylinositol (GPI) anchors. 

Application to glycosylphosphatidylinositol (CPI) anchor and inositol phosphoglycan (IPG) synthesis... 

From NPOEs to the Synthesis of a Malaria Candidate Glycosylphosphatidylinositol (CPI)... 

Hundt, M., Schmidt, R.E. (1992). The glycosylphosphatidylinositol-linked Fc/receptor III represents the dominant receptor structure for immune complex activation of neutrophils. Eur. J. Immunol. 22, 811-16. 

Furthermore, according to Howell and Crine (1996), type IV represents multimers of subunits, type V represents proteins that are anchored to the membrane by a covalently linked lipid moiety only, and type VI represents those anchored both by a transmembrane domain and the glycosylphosphatidylinositol (GPI) anchor (see Section III,C,3). 

The last class of three major membrane anchors is caused by the modification by a glycophospholipid, glycosylphosphatidylinositol (GPI) (Udenfriend and Kodukula, 1995a Takeda and Kinoshita, 1995). They are observed in many eukaryotes, especially in protozoa and yeasts. Unlike other classes, the GPI-anchored proteins are exposed at the (extracytoplasmic) surface of the plasma membrane. Thus, we can predict the localization at the plasma membrane from the presence of a GPI anchor, although some of them are further incorporated into the cell wall in S. cerevisiae (as described in Section III,K,1). 

Antony, A. C., and Miller, M. E. (1994). Statistical prediction of the locus of endoproteo-lytic cleavage of the nascent polypeptide in glycosylphosphatidylinositol-anchored proteins. Biochem. J. 298, 9-16. 

Hamada, K., Fukuchi, S., Arisawa, M., Baba, M., and Kitada, K. (1998a). Screening for glycosylphosphatidylinositol (GPI)-dependent cell wall proteins in Saccharomyces cere-visiae. Mol. Gen. Genet. 258, 53-59. 

Udenfriend, S., and Kodukula, K. (1995a). How glycosylphosphatidylinositol-anchored membrane proteins are made. Annu. Rev. Biochem. 64, 563—591. 

Cytosolic CA II is widespread through tissues, the kidney possesses CA IV which is anchored to the cell membrane of the luminal PCT brush border by linkage with a membrane phospholipid, glycosylphosphatidylinositol. Such luminal positioning allows the enzyme to act upon filtered bicarbonate ions as they enter the tubule. 

Molecular targets have been elucidated for Dm-AMPl and Rs-AFP2. Dm-AMPl was found to bind plasma membranes from Neurospora crassa and Saccharomyces cerevisiae in a saturable manner and it competed with closely related defensins for binding. Mutational studies with S. cerevisiae identified lipid raffs containing sphingolipids as a molecular target " while glycosylphosphatidylinositol (GPI)-anchored proteins could be... 

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