Mucins biosynthesis

Fig. 2.4 Biosynthesis of gel-forming mucins. Schematic representation of the major steps occurring during the biosynthesis of mucins. Mucin biosynthesis is a sequential process that starts in the endoplasmic reticulum and ends in the trans-compartments of the Golgi complex. Formation of disulfide-linked oligomers/multimers involves two steps dimerization in the endoplasmic reticulum and interdimeric disulfide bonding in the Golgi complex. O-Glycosy-lation of dimeric precursors results in more extended but still flexible chains. See text for further details. Rectangles indicate the NH-terminal D-domains while circles and the bars represent the COOH-terminal CK-domains and the O-glycan chains, respectively...

FIGURE 10. The alternative pathways for mucin biosynthesis. Sialic acid addition prevents further sugar additions. Wavy line represents polypeptide backbone of submaxillary mucin. 

Mucins are a class of O-linked glycoproteins that are distributed on the surfaces of epithelial cells of the respiratory, gastrointestinal, and reproductive tracts. The Golgi apparatus plays a major role in glycosyla-tion reactions involved in the biosynthesis of glycoproteins. 

T. A. Gerken, Kinetic modeling confirms the biosynthesis of mucin core 1 (/i-Gal (1 -3)x-Gal YAc-O-Ser/Thr) O-glycan structures are modulated by neighboring glycosylation effects, Biochemistry, 43 (2004) 4137—4142. 

The mucins are the predominant O-linked glycoproteins and may be divided into eight different core structures, depending on the relative occurrence of various glycosyl-transferases at the location of their biosynthesis (Table i),. 182-183,264,265]... 

O-glycans. Recently, evidence for the existence of inborn errors in the biosynthesis of core 1 mucin type O-glycans have been described [30]. 

Argueso P, Gipson IK (2001) Epithelial mucins of the ocular surface structure, biosynthesis and function. Exp Eye Res 73(3) 281—289... 

Figure 4 Overview of mucin-type 0-linked glycoprotein biosynthesis. The production of the eight core structures found in 0-glycans is shown along with the enzymes and nucleotide sugars that are involved in each step. Additional information on the enzymes shown can be found in the KEGG databases (see the Legend for Fig. 3).

Here, we delineate the biosynthetic pathways of the most common types of protein glycosylation occurring in the secretory pathway mucin-type O-linked glycosylation, A-linked glycosylation, and the formation of glycosaminoglycans. In addition, we will briefly visit the biosynthesis of some less-common varieties of protein glycosylation. 

KSII biosynthesis is initiated by the formation of mucin-type core 2 disaccharide (103). KSn is usually capped with siahc acid at either C3 or C6 of terminal GlcNAc. Sulfated GlcNAc in KSn is often modified with al-3-hnked fucose, although uot within four sugars of the terminus (104). 

Inhibition of the initiating ppGalNAcTs is an alternative strategy for obstructing mucin-type biosynthesis. A uridine-based... 

Tabak LA In defense of the oral cavity Structure, biosynthesis, and function of salivary mucins. Annu Rev Physiol 1995 57 547-564. 

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