Phosphorylcholine esterase is critical for Dolichos biflorus and Helix pomatia agglutinin binding to pneumococcal teichoic acid

Streptococcus pneumoniae (the pneumococcus) has wall teichoic acid (WTA) and lipoteichoic acid (LTA) expressing the Forssman antigen (FA). Two lectins, Dolichos biflorus agglutinin (DBA) and Helix pomatia agglutinin (HPA), are known to bind FA. To determine the molecular structure targeted by these two lectins, different pneumococcal strains were studied for DBA/HPA binding with flow cytometry and fluorescence microscopy. Genetic experiments were used to further examine the lectins' molecular target. Twelve strains were positive for DBA binding, whereas three were negative. Super-resolution microscopy showed that DBA stained only the subcapsular area of pneumococci. The three DBA nonbinders showed no phosphorylcholine esterase (Pce) activity in vitro, whereas 10 DBA binders displayed Pce activity (the remaining two strains were DBA binders with no Pce activity in vitro). The pcegene sequence for 10 representative strains revealed two functional pce alleles, the previously recognized "allele A" and a newly discovered "allele B" (with 12 additional nucleotides). Isolates with allele B showed no Pce activity in vitro but did bind to DBA, indicating allele B Pce is functional in vivo. Genetic transfer experiments confirmed that either allele is sufficient (and necessary) for DBA binding. The three DBA nonbinders had various mutations that affected Pce function. Observations with HPA were identical to those with DBA. We show that DBA and HPA bind only to the WTA/LTA of pneumococcal isolates with a functional Pce enzyme. A newly discovered Pce variant (allele B) is functional in vivo but nonfunctional when assayed in vitro.

Embryoglycan: a highly branched poly-N-acetyllactosamine in pluripotent stem cells and early embryonic cells

Embryonal carcinoma cells, stem cells of teratocarcinomas, are pluripotent stem cells and also prototypes of embryonic stem cells. Embryonal carcinoma cells contain large amounts of a highly branched poly-N-acetyllactosamine called embryoglycan, which has a molecular weight of approximately 10,000 or greater, and is asparagine-linked. This glycan was found by analyses of fucose-labeled glycopeptides, and its characteristics were established by biochemical analyses. The content of embryoglycan progressively decreases during the in vitro differentiation of embryonal carcinoma cells. Embryoglycan is also abundant in mouse embryonic stem cells and preimplantation mouse embryos, and decreases during embryogenesis. Embryoglycan carries a number of carbohydrate markers of murine pluripotent stem cells. Lewis x markers, such as SSEA-1, 4C9 antigen, and binding sites for Lotus tetragonolobus agglutinin are of particular importance. 4C9 antigenicity requires clustering of Lewis x, best accomplished by poly-N-acetyllactosamine branching, whereas SSEA-1 does not. Although in vivo evidence is lacking, these epitopes have been suggested to participate in cell-to-cell and cell-to-substratum adhesion. Other markers on embryoglycan include α-galactosyl antigens such as ECMA-2, and binding sites for Dolichos biflorus agglutinin, the epitope of which is considered to be identical to Sd^a antigen, namely, GalNAcβ1-4(NeuAcα2-3)Galβ1-4GlcNAc. While embryoglycan is also present in human teratocarcinoma cells, the carbohydrate markers characterized in human pluripotent stem cells to date are largely carried by glycolipids and keratan sulfate. Information on embryoglycan and markers carried by it may assist in the development of new markers of human pluripotent stem cells and their progenies.

The expanding roles of the Sd(a)/Cad carbohydrate antigen and its cognate glycosyltransferase B4GALNT2

BACKGROUND

The histo-blood group antigens are carbohydrate structures present in tissues and body fluids, which contribute to the definition of the individual immunophenotype. One of these, the Sd(a) antigen, is expressed on the surface of erythrocytes and in secretions of the vast majority of the Caucasians and other ethnic groups.

SCOPE OF REVIEW

We describe the multiple and unsuspected aspects of the biology of the Sd(a) antigen and its biosynthetic enzyme β1,4-N-acetylgalactosaminyltransferase 2 (B4GALNT2) in various physiological and pathological settings.

MAJOR CONCLUSIONS

The immunodominant sugar of the Sd(a) antigen is a β1,4-linked N-acetylgalactosamine (GalNAc). Its cognate glycosyltransferase B4GALNT2 displays a restricted pattern of tissue expression, is regulated by unknown mechanisms - including promoter methylation, and encodes at least two different proteins, one of which with an unconventionally long cytoplasmic portion. In different settings, the Sd(a) antigen plays multiple and unsuspected roles. 1) In colon cancer, its dramatic down-regulation plays a potential role in the overexpression of sialyl Lewis antigens, increasing metastasis formation. 2) It is involved in the lytic function of murine cytotoxic T lymphocytes. 3) It prevents the development of muscular dystrophy in various dystrophic murine models, when overexpressed in muscular fibers. 4) It regulates the circulating half-life of the von Willebrand factor (vWf), determining the onset of a bleeding disorder in a murine model.

GENERAL SIGNIFICANCE

The expression of the Sd(a) antigen has a wide impact on the physiology and the pathology of different biological systems.

The lectin of Dolichos biflorus agglutinin recognises glycan epitopes on the surface of a subset of cardiac progenitor cells

The discovery of adult cardiac progenitor cells (CPCs) provides a promising way for treating heart disease; however, their surface characteristics that play a critical role in regulating their maintenance, self-renewal, migration, and differentiation have not been fully investigated. One subpopulation of Dolichos biflorus agglutinin (DBA)-positive cells was identified in the heart of adult mice. Flow cytometry showed that 3.7% of heart cells could be labeled by FITC conjugated DBA. BrdU pulse-chase showed that 55-75% of DBA(+) cells were CPCs. Evidences from 5-FU-induced myelosuppression along with BrdU pulse-chasing suggests that DBA-positive cells are proliferative. Furthermore, DBA positive cells display a cologenic appearance in vivo. Our findings suggest that DBA-positive cells in the heart of adult mouse contained a subset of CPCs, and DBA reactivity is one novel surface characteristic on CPCs.