High mannose sequences

Figure 6.2 A. The Mannosyl Residues (Heavy Type) that can be Phosphorylated in Lysosomal High-Mannose Sequences (from the data of Varki and Komfeld, 1980). Residue Ic may also be available. B. A possible scheme by which they may be related. Some glucosylated strictures can also become phosphorylated (Gabel and Komfeld, 1982).

Similar results were recently obtained with a human monoclonal antibody, with KDEL sequences fused to the C-termini of both heavy chains, expressed in tobacco [33]. As observed for the invertase-HDEL fusion, about 90% of the N-linked glycans on this antibody were of the high-mannose type, with 6-9 mannose residues, while a fraction contained the immunogenic P(l,2)-xylose glyco-epitope (Fig. 15.6). However, this antibody was not a(l,3)-fucosylated, a glycan modification occurring in the trans Golgi [34]. 

Peripheral to the Gal-GlcNAc sequences of glycoproteins, there can occur an array of blood-group-related glycosylations, anionic substitutions (sialy-lation, 0-sulfation, and 0-phosphorylation), or both. Chains of the high-mannose type may also bear phosphate groups. Table VI reviews the pat-... 

EG III 397 AB-core aa sequence in part from protein and in full from gene (egl3), high mannose content 47 mole/mole enzyme, hydrophobic cluster analysis... 

During the transfer of the nascent peptide into the lumen of the cistern ae of the endoplasmic reticulum, the leader sequence is cleaved off. The glycoproteins remain anchored into the membrane by either their N- or carboxyl-terminus. The attachment of the oligosaccharide occurs concomitantly with the synthesis of the protein. As discussed in Section 11,2, this is a high-mannose structure that can be modified during transport on intracellular membranes, and then yields a complex type. 

There is one molecule each of apoLp-I and apoLp-lI in each lipophorin molecule (Shapiro et al., 1984 Surholt et al., 1992). A similar amino acid composition, as well as the presence of oligosaccharide chains of the high-mannose type, has been observed for apoLp-I and apoLp-II from different insect species (Pattnaik et al., 1979 Ryan et al., 1984 Shapiro et al., 1984 Kashiwazaki and Ikai, 1985 Dillwith et al., 1986 Nagao and Chino, 1987 Rimoldi o/., 1991). Both apolipoproteins are water insoluble when separated from lipophorin, and in this regard resemble vertebrate apoB. No amino acid sequence data, either from direct or cDNA... 

The saccharide sequence of Asn-(GlcNAc)2PMan(aMan)2, in complex stractures is tenned the core and the residues of N-acetylglucosamine within it are internal . Those in outer chains are external . If a residue of GlcNAc is attached to the mannosyl residue it is called a bisecting iV-acetylglucosamine. The use of the word core in high-mannose and intermediate structures is rather less precise. 

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