O-Glucosyl and O-fucosyl glycans are also rare types of protein glycosylations that have been found in the epidermal growth factor homology regions (EGF modules) of some human proteins.
The nucleotide sugars are biosynthesized in the cytosol, and their monosaccharides must be translocated into the lumen of the ER and/or Golgi before they can be used for the glycosylation process.
As observed in the case of patients with CDG-IIc who have a deficient GDP-Fuc transporter (FUCT) (48) and in a patient with CDG-IIf who has a deficient CMP-NeuAc transporter (49), abnormal glycosylation results from diminished NST function.
The presence of multienzyme complexes is likely to be functionally relevant in the regulation of glycosylation and contribute to the maintenance of the steady-state localization of the Golgi glycosyltransferases (72).
The effects of O-linked glycosylation on the bioactivity of many signaling molecules, particularly hormones and cytokines, and a relatively small number of enzymes, have been described.
Finally, O-linked glycosylation is essential for the expression and processing of particular proteins.
Because there is no N-linked glycosylation site in preproBNP, our data indicate that secreted HMW proBNP is O-glycosylated (Fig.
GLYCOSYLATION OF proBNP AT T71-RESIDUE CONTROLS THE LEVELS OF EXTRACELLULAR proBNP
2 and 3), we hypothesized that the glycosylation at the T71 residue also plays the key role in the secretion of glycosylated proBNP.
These observations suggest that neither furin nor corin cleaved intracellular proBNP, even when the T71 glycosylation was ablated.
Extracellular BNP32 was below the detectable concentration, indicating that glycosylation of preproBNP at residue T71 also controlled the concentrations of extracellular proBNP in cardiomyocyte cultures.
Moreover, the T71A mutant, which ablates one of the O-glycosylation sites near the proBNP cleavage site (71TLRAPR [down arrow] S, with T71 glycosylation site and RXXR 2 [down arrow] protease recognition/cleavage sequence), resulted in severe reduction in the extracellular proBNP.