Mucin golgi complex

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...

Once the mucin dimeric precursors reach the Golgi complex, they are O-glycosylated and N-glycosylation is completed. In vitro studies with purified, de-glycosylated gel-forming mucins (Rose et al. 1984, Shogren et al. 1989 ... 

In breast cancer cells, the synthesis of 0-glycan core 1 and 2 structures occurs mainly in the cis—medial Golgi compartment with some overlap toward the medial Golgi. The sialyltransferase ST3Gal-I that acts on core 1 substrate has been shown to be localized by immunocytochemistry mainly to the medial and trans Golgi compartments in mammary cells. Its localization therefore partially overlaps with that of C2GnTl. Transfection experiments prove that the competition between the two enzymes indeed takes place. Thus the relative expression levels and activities of these two enzymes control the relative distribution of either highly sialylated or complex chains with core 2 structures of MUCl mucin. ... 

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