Transport glycoprotein

Griffin, J. W., Price, D. L., Drachman, D. B. and Morris, J. Incorporation of axonally transported glycoproteins into axolemma during nerve regeneration. /. Cell Biol. 88, 205-214,1981. 

Danbolt, N. C., Pines, G., and Kanner, B. I. (1990) Purification and reconstitution of the sodium- and potassium-coupled glutamate transport glycoprotein from rat brain. Biochemistry 29,6734-6740. 

Radian, R., Bendahan, A Kanner, B.I. (1986). Purification and identification of the functional sodium- and chloride-coupled y-aminobutyric acid transport glycoprotein from rat brain. J. Biol. Chem. 261,15437-15441. 

Transferrin (Tf), the iron transport glycoprotein found in the biological fluids of vertebrates, is also synthesized by oligodendrocytes in the CNS. Overexpressing Tf in the brain of transgenic mice accelerates oligodendrocyte maturation, early maturation of the cerebellum and spinal cord, and myelination in the corpus callosum (Sow et al., 2006). The association of IGF-1 and transferrin favors remyelination in the myelin deficient rat (Espinosa-Jeffrey et al., 2006). 

Kim R, Fromm MF, Wandel C, Leake B, Wood AJ, Roden DM, et al. The drug transporter / -glycoprotein limits oral absorption and brain entry of HIV-1 protease inhibitors. J Clin Invest 1998 101 289-94. 

Puromycin. Puromycin (19), elaborated by S. alboniger (1—4), inhibits protein synthesis by replacing aminoacyl-tRNA at the A-site of peptidyltransferase (48,49). Photosensitive analogues of (19) have been used to label the A-site proteins of peptidyltransferase and tRNA (30). Compound (19), and its carbocycHc analogue have been used to study the accumulation of glycoprotein-derived free sialooligosaccharides, accumulation of mRNA, methylase activity, enzyme transport, rat embryo development, the acceptor site of human placental 80S ribosomes, and gene expression in mammalian cells (51—60). 

The mechanism of inhibition has not been characterized, but it is probably related to the ionophoretic properties of these antibiotics. Monensin has been shown to inhibit the intracellular transport of viral membrane proteins of cells infected with Semliki Forest vims (169). The formation of syncytia, normally observed when T-lymphoblastoid cell line (CEM) cells are cocultivated with human immunodeficiency vims (HlV-l)-infected T-ceU leukemia cell line (MOLT-3) cells, was significantly inhibited in the presence of monensin (170). This observation suggests that the viral glycoproteins in the treated cells were not transported to the cell surface from the Golgi membrane. 

Many proteins found in nature are glycoproteins because they contain covalently linked oligo- and polysaccharide groups. The list of known glycoproteins includes structural proteins, enzymes, membrane receptors, transport proteins, and immunoglobulins, among others. In most cases, the precise function of the bound carbohydrate moiety is not understood. 

P-glycoprotein (P-gp) works as a transporter at the intestinal mucosa pumping drugs out into the lumen. Absorption of P-gp substrates, such as digoxin, cyclosporine, etc., can be increased by inhibitors of P-gp and reduced by inducers. 

A family of related, membrane-spanning glycoproteins that catalyze the transport of glucose across a lipid bilayer of the plasma membrane along a concentration gradient. 

Both influx and efflux transporters are located in intestinal epithelial cells and can either increase or decrease oral absorption. Influx transporters such as human peptide transporter 1 (hPEPTl), apical sodium bile acid transporter (ASBT), and nucleoside transporters actively transport drugs that mimic their native substrates across the epithelial cell, whereas efflux transporters such as P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and breast cancer resistance protein (BCRP) actively pump absorbed drugs back into the intestinal lumen. 

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