Resistance to Bacillus thuringiensis toxin in Caenorhabditis elegans from loss of fucose

A mutation in the Caenorhabditis elegans bre-1 gene was isolated in a screen for Bacillus thuringiensis toxin-resistant (bre) mutants to the Cry5B crystal toxin made by B. thuringiensis. bre-1 mutant animals are different from the four other cloned bre mutants in that their level of resistance is noticeably lower. bre-1 animals also display a significantly reduced brood size at 25 degrees C. Here we cloned the bre-1 gene and characterized the bre-1 mutant phenotype. bre-1 encodes a protein with significant homology to a GDP-mannose 4,6-dehydratase, which catalyzes the first step in the biosynthesis of GDP-fucose from GDP-mannose. Injection of GDP-fucose but not fucose into C. elegans intestinal cells rescues bre-1 mutant phenotypes. Thus, C. elegans lacks a functional fucose salvage pathway. Furthermore, we demonstrate that bre-1 mutant animals are defective in production of fucosylated glycolipids and that bre-1 mutant animals make quantitatively reduced levels of glycolipid receptors for Cry5B. We finally show that bre-1 mutant animals, although viable, show a lack of fucosylated N- and O-glycans, based on mass spectrometric evidence. Thus, C. elegans can survive with little fucose and can develop resistance to crystal toxin by loss of a monosaccharide biosynthetic pathway.

Dysregulation of TGF-beta1 receptor activation leads to abnormal lung development and emphysema-like phenotype in core fucose-deficient mice

The core fucosylation (alpha1,6-fucosylation) of glycoproteins is widely distributed in mammalian tissues, and is altered under pathological conditions. To investigate physiological functions of the core fucose, we generated alpha1,6-fucosyltransferase (Fut8)-null mice and found that disruption of Fut8 induces severe growth retardation and death during postnatal development. Histopathological analysis revealed that Fut8(-/-) mice showed emphysema-like changes in the lung, verified by a physiological compliance analysis. Biochemical studies indicated that lungs from Fut8(-/-) mice exhibit a marked overexpression of matrix metalloproteinases (MMPs), such as MMP-12 and MMP-13, highly associated with lung-destructive phenotypes, and a down-regulation of extracellular matrix (ECM) proteins such as elastin, as well as retarded alveolar epithelia cell differentiation. These changes should be consistent with a deficiency in TGF-beta1 signaling, a pleiotropic factor that controls ECM homeostasis by down-regulating MMP expression and inducing ECM protein components. In fact, Fut8(-/-) mice have a marked dysregulation of TGF-beta1 receptor activation and signaling, as assessed by TGF-beta1 binding assays and Smad2 phosphorylation analysis. We also show that these TGF-beta1 receptor defects found in Fut8(-/-) cells can be rescued by reintroducing Fut8 into Fut8(-/-) cells. Furthermore, exogenous TGF-beta1 potentially rescued emphysema-like phenotype and concomitantly reduced MMP expression in Fut8(-/-) lung. We propose that the lack of core fucosylation of TGF-beta1 receptors is crucial for a developmental and progressive/destructive emphysema, suggesting that perturbation of this function could underlie certain cases of human emphysema.

Generation of Arabidopsis thaliana plants with complex N-glycans lacking beta1,2-linked xylose and core alpha1,3-linked fucose

The plant glycosyltransferases, beta1,2-xylosyltransferase (XylT) and core alpha1,3-fucosyltransferase (FucT), are responsible for the transfer of beta1,2-linked xylose and core alpha1,3-linked fucose residues to glycoprotein N-glycans. These glycan epitopes are not present in humans and thus may cause immunological responses, which represent a limitation for the therapeutic use of recombinant mammalian glycoproteins produced in transgenic plants. Here we report the genetic modification of the N-glycosylation pathway in Arabidopsis thaliana plants. Knockout plants were generated with complete deficiency of XylT and FucT. These plants lack antigenic protein-bound N-glycans and instead synthesise predominantly structures with two terminal betaN-acetylglucosamine residues (GlcNAc(2)Man(3)GlcNAc(2)).

Alpha 1,6-linked fucose affects the expression and stability of polysialic acid-carrying glycoproteins in Chinese hamster ovary cells

To determine the effect of alpha1,6-linked fucose modification of N-glycans on the expression of polysialic acids (PSAs), the expression of PSAs in a fucose-lacking mutant of Chinese hamster ovary (CHO) cells, Lec13, was compared with that in CHO K1 cells. PSA synthase activity in these cells and the antennary structures of N-glycans associated with the neural adhesion molecule (NCAM), which is a major PSA-carrying glycoprotein, did not differ between the two types of cells. Metabolic labeling of cells with [3H]glucosamine for 48 h followed by immunoprecipitation with anti-PSA monoclonal antibodies revealed that the amount of labeled PSA-carrying glycoproteins obtained from Lec13 cells was 10-times less than that from K1 cells, although the incorporation of [3H]glucosamine into total extracts and NCAM was almost the same. In contrast, when cells were pulse labeled with [35S]methionine followed by a 1 h chase, there was not such a great difference in PSA-carrying protein synthesis between K1 and Lec13 cells. However, during a prolonged chase period, PSA-carrying proteins rapidly decreased in Lec13 cells, whereas those in K1 cells did not change. The degradation of PSA-carrying glycoproteins in Lec13 cells was partly prevented when the cells were grown in fucose-containing medium. Therefore, fucose modification of core N-glycans may affect the efficient expression of PSAs through the intracellular stability of PSA-carrying glycoproteins.