We have previously reported that 1-benzyl-2-acetamido-2-deoxy-α-d-galactopyranoside (GalNAcα-O-bn), an inhibitor of glycosylation, perturbed apical biosynthetic trafficking in polarized HT-29 cells suggesting an involvement of a lectin-based mechanism. Here, we have identified galectin-4 as one of the major components of detergent-resistant membranes (DRMs) isolated from HT-29 5M12 cells. Galectin-4 was also found in post-Golgi carrier vesicles. The functional role of galectin-4 in polarized trafficking in HT-29 5M12 cells was studied by using a retrovirus-mediated RNA interference. In galectin-4–depleted HT-29 5M12 cells apical membrane markers accumulated intracellularly. In contrast, basolateral membrane markers were not affected. Moreover, galectin-4 depletion altered the DRM association characteristics of apical proteins. Sulfatides with long chain-hydroxylated fatty acids, which were also enriched in DRMs, were identified as high-affinity ligands for galectin-4. Together, our data propose that interaction between galectin-4 and sulfatides plays a functional role in the clustering of lipid rafts for apical delivery.

Mucin glycans were isolated from different regions of the normal human intestine (ileum, cecum, transverse and sigmoid colon, and rectum) of two individuals with ALe b blood group. A systematic study of the monosaccharides and oligosaccharide alditols released by reductive ␤-elimination from mucins was performed using gas chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and nuclear magnetic resonance spectroscopy techniques. Important variations were observed in the mucin-associated oligosaccharide content with an increasing gradient of sialic acid from the ileum to the colon associated with a reverse gradient of fucose. Moreover, a comparative study of the Sda/Cad and ABH blood group determinants along the gastrointestinal tract showed the same reverse distribution in the two kinds of antigens. In addition, besides their heterogeneity, sialic acids presented considerable variations in the degree of O-acetylation in relation to glycan sialylation level. These data are discussed in view of recent concepts suggesting that the oligosaccharide composition of the gut constitutes a varied ecosystem for microorganisms that are susceptible to adapt there and possess the specific adhesion system and specific enzymes able to provide a carbohydrate nutrient.Mucins are very high molecular weight glycoproteins secreted by mucosae or some exocrine glands into the lumen of the respiratory, gastrointestinal, and reproductive tracts (1). They consist of a protein backbone with hundreds of carbohydrate side chains of varying lengths, sequences, compositions, and anomeric linkages. A distinguishing feature of mucins is that they contain O-linked oligosaccharides, i.e. the sugar chains are attached to the peptide backbone via a O-glycosidic linkage between a Ser or Thr residue and a GalNAc 1 residue.Intestinal mucins are mainly produced by goblet cells but also by enterocytes and occur both as soluble-secreted and membrane-bound forms. High glycosylation and high mass structures give the mucins gel-forming abilities and other general physical properties that have been regarded as having a protective and rheological function at mucosal surfaces (2). The identification of several different encoded mucins and an enormous repertoire of possible mucin oligosaccharides indicate that the tasks for these glycoproteins may be more subtle than their macroscopic properties suggest. Indeed, mucins may also provide precise structural information carried in determinants among their glycans and in the peptide core, which could mediate specific binding of antibodies, pathogenic microbes, and leukocytes, and may be important in host-pathogen interactions, inflammation, and cancer metastasis (3)(4)(5)(6)(7)(8).Consistent data indicate that mucin genes are expressed in a regulated cell-and tissue-specific manner in the intestine. In situ hybridization has demonstrated that MUC2 is expressed only in goblet cells in the intestine, whereas MUC3 is expressed in both goblet cells and absorptive cells (9). Moreo...

We have cloned a novel protein kinase from human cerebellum and named it LZK (leucine zipper-bearing kinase). The LZK cDNA encoded a 966-amino acid polypeptide that contains a kinase catalytic domain and double leucine/isoleucine zippers separated by a short spacer region. The amino acid sequence of the kinase catalytic domain was a hybrid between those in serine/ threonine and tyrosine protein kinases, indicating that LZK belongs to the subfamily of the mixed lineage kinase (