The Glycosylation of Rat Intestinal Muc2 Mucin Varies between Rat Strains and the Small and Large Intestine

The large glycosylated domains obtained from the rat intestinal mucin Muc2 were isolated from the large and small intestine of the inbred rat strains GOT-W and GOT-BW. The expression of the rat Muc2 in the large intestine was confirmed immunochemically and by Northern blotting. Released oligosaccharides were structurally characterized by gas chromatography-mass spectrometry (neutral and sialylated species) or by tandem mass spectrometry (sulfated species), and a total of 63 structures was assigned. The large intestinal oligosaccharides were found to be identical between the strains, while the small intestinal glycosylation differed. Until now, detailed structural analysis of oligosaccharides isolated from a single mucin core or mucin domain with different origin have not been performed, and the information of different mucin glycoforms has been limited to immunochemistry. Blood group A-determinants (GalNAca1‐3(Fuca1‐2)Galb1-, and structures related to the blood group Sd a /Cad-related epitope NeuAc/NeuGca1‐ 3(GalNAcb1‐4)Galb1-, were found in GOT-BW small intestine, and also in both large intestines. Blood group Hdeterminants and NeuAc/NeuGca1‐3Galb1- were found in all samples. Core 1 (Galb1‐3GalNAca1-), core 2 (Galb1‐3(GlcNAcb1‐ 6)GalNAca1-), core 3 (GlcNAcb1‐3GalNAca1-), and core 4 (GlcNAcb1‐3(GlcNAcb1‐ 6)GalNAca1- were also found in all the samples. The large intestine were enriched in sulfated oligosaccharides and the small intestine contained higher amounts of sialylated species. Sulfation were found exclusively on C-6 of GlcNAc. The family of highly glycosylated glycoproteins found at the mucosal surfaces are known as mucins (1). Characteristic for mucins is the high degree of O-linked glycosylation known as the mucin-type, where a-N-acetylgalactosamine is linked to serine or threonine of the protein backbone. These amino acids together with proline are mainly found in long and often repeated protein sequences, called mucin domains, that become a scaffold for the glycosylation. The mucins are largely responsible for the physical properties of mucus that serves as a lubricant for the mucosal surface and protects the underlying epithelium from mechanical and chemical stress. However, the identification of several different encoded mucins, and an enormous repertoire of possible mucin oligosaccharides indicates that the tasks for these glycoproteins may be more subtle than the macroscopic properties suggest. Mucins produced in the intestine are mainly derived from the goblet cells. The major part (at least 80%) of the rat intestinal mucins, measured as protease-resistant mucin domains, can be recovered as an “insoluble” glycoprotein complex in as denaturating conditions as 6.0 M guanidinium chloride (2), providing that shear homogenization is avoided. Two highly glycosylated peptides, named glycopeptide A (gpA) 1 and B (gpB), 650 kDa and 335 kDa, respectively, were