N-linked carbohydrate chains

Fig. 3. Human CG, hLH, and equine CG (eCG) P-subunits. Amino acid numbeiing is relative to maximum homology between the three subunits. Consensus glycosylation sites ate at Asn-13 and 30. = same amino acid as hCG/3. Underlined Asn residues indicate attachment of N-linked carbohydrate chains. Serines at positions 121, 127, 132, and 138 of hCGP are underlined to indicate sites of O-linked carbohydrate attachment. Residues 115—118,...

Amgen has recently introduced darbe-poetin Aranesp), a long-acting version of human erythropoietin. With two additional N-linked carbohydrate chains, darbepoetin contains more sialic acid than epoetin alfa and has an approximately threefold longer half-life, which leads to less frequent dosing than epoetin alfa. Darbepoetin is approved for both the treatment of anemia due to chronic renal failure and the treatment of chemotherapy-induced anemia. 

IFN 3 is produced in vivo normally by fibroblasts. In humans, only one IFN 3 is found, which has 166 amino acids and a molar mass larger than 20 kDa. The molecule has a disulfide bond as well as an N-linked carbohydrate chain bound to asparagine 80. Structurally, it is characterized by the presence of five a-helices. Recombinant IFN 3 is marketed under the names of Betaferon , Betaseron , Avonex , and Rebif , being indicated for the treatment of multiple sclerosis, since it blocks the secretion of other cytokines involved in the pathogenesis of this disease. 

Korrel SA, Clemetson KJ, van Halbeek H, Kamerling JP, Sixma JJ, Vliegenthart JF. Identification of a tetrasialylated monofiioosylated tetraantennaiy N- linked carbohydrate chain in human platdet glycocalian. FEBS Lett 1988 228 321-6. 

A. S. Couto, M. F. Goncalves, W. Colli, and R. M. de Lederkremer, The N-linked carbohydrate chain of the 85-kilodalton glycoprotein from Trypanosoma cruzi trypomastigotes contains sialyl, fucosyl and galactosyl (alpha l-3)galactose units, Mol. Biochem. Parasitol., 39 (1990) 101—107. 

N-linked carbohydrate chain from Androctonus australis hemocyanin [15]... 

N-linked carbohydrate chains from Astacus leptodactylus hemocyanin [16]... 

The H3a,3e/NAc structural reporters of NeuSAc have proved to be suitable in studying sialylation reactions in terms of positional specificity and branching (N-linked carbohydrate chains) specificity, using different sialyltransferases and CMP-NeuSAc as donor [333-335] (see also section 6.3). 

In the Fc of IgG [9,23] the two CH3 domains are paired in a pattern similar to that found for the CH1-CL interaction (Fig. 6). The two CH2 domains show no close interaction but have interposed between them two branched N-linked carbohydrate chains which make little contact between one another in human Fc [23] but more extensive contact in rabbit Fc [30]. In the pairing of the CH3 domains, approximately 1000 A2 of surface per domain is involved in the interaction. In the Ch2 case the carbohydrate provides a substitute for the domain-domain contact and helps to stabilise the CH2 domain. However, the CH2-carbohydrate contact area is only about half that of, for example, the CH3-CH3 contact so that one might expect a lower inherent stability for the CH2 domain. Indeed the CH2 domain is more sensitive to proteolytic degradation than the other domains of IgG [24], Domain stability has also been related to the apparent softness of parts of the CH2 domain most remote from the CH2-CH3 interface as indicated by large temperature factors or missing electron density in the crystal analysis of human Fc [23]. A corresponding softness has not, however, been found for rabbit Fc (Sutton B.J., personal communication). Tables 1 and 2 show a comparison of known CH3 and CH2 sequences. 

N indicates that an N-linked carbohydrate chain is attached to Asn-297 (note signal sequence Asn-x-Thr). u indicates unsequenccd. A dot indicates no residue at the position corresponding to the numbered IgG 1 residue. Cys-261 bridges to Cys-321 close to Trp-277. Allotypic substitutions occur at positions 291, 296, 309 and 339 [123],... 

The Ca3 domain of secreted IgA possesses an 18-residue tailpiece which is very similar to that found for C A and similarly has an N-linked carbohydrate chain and a penultimate cysteine residue. 

Number of N-linked carbohydrate chains per heavy chain constant region 1 1 1 1 5 2 5 3 6... 

A. A. Bergwerff, J. Van Oostrum, J. P. Kamerling, J. F. Vliegenthart, The major N-linked carbohydrate chains from human urokinase. The occurrence of 4-O-sulfated, (alpha 2-6)-sialylated or (alpha l-3)-fucosylated N-acetylgalactosamine(beta l-4)-N-acetylglucosamine elements. Eur. J. Biochem. 1995 228, 1009-19. 

Kubelka, V, Altmann, F., Staudacher, E., Tretter, V, Marz, L., Hard, K., Kammerling, J.R, and Vliegenter, J.F., 1993, Primary structures of the N-linked carbohydrate chains from honeybee venom phospholipase A2. Eur. J. Biochem. 213 1193-1204. 

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