Glycosylation of a CNS-specific extracellular matrix glycoprotein, tenascin-R, is dominated by O-linked sialylated glycans and "brain-type” neutral N-glycans

As a member of the tenascin family of extracellular matrix glycoproteins, tenascin-R is located exclusively in the CNS. It is believed to play a role in myelination and axonal stabilization and, through repulsive properties, may contribute to the lack of regeneration of CNS axons following damage. The contrary functions of the tenascins have been localized to the different structural domains of the protein. However, little is known concerning the influence of the carbohydrate conjugated to the many potential sites for N- and O-glycosylation (10-120% by weight). As a first analytical requirement, we show that >80% of the N-glycans in tenascin-R are neutral and dominated by complex biantennary structures. These display the "brain-type” characteristics of outer-arm- and core-fucosylation, a bisecting N-acetylglucosamine and, significantly, an abundance of antennae truncation. In some structures, truncation resulted in only a single mannose residue remaining on the 3-arm, a particularly unusual consequence of the N-glycan processing pathway. In contrast to brain tissue, hybrid and oligomannosidic N-glycans were either absent or in low abundance. A high relative abundance of O-linked sialylated glycans was found. This was associated with a significant potential for O-linked glycosylation sites and multivalent display of the sialic acid residues. These O-glycans were dominated by the disialylated structure, NeuAcα2-3Galβ1-3(NeuAcα2-6)GalNAc. The possibility that these O-glycans enable tenascin-R to interact in the CNS either with the myelin associated glycoprotein or with sialoadhesin on activated microglia is discusse

Glycosylation of a CNS-specific extracellular matrix glycoprotein, tenascin-R, is dominated by O-linked sialylated glycans and “brain-type” neutral N-glycans

ISSN:0959-665

A Proteomic Approach for the Discovery of Early Detection Markers of Hepatocellular Carcinoma

Individuals chronically infected with hepatitis B or C virus (HBV, HCV) are at high risk for the development of hepatocellular carcinoma (HCC), with disease progression occurring relentlessly over many years. The diagnosis of HCC usually occurs at late stages in the disease when there are few effective treatment options and the prognosis for patients with HCC is very poor. The long latency period, together with clearly identified at risk populations, provide opportunities for earlier detection that will allow more timely and effective treatment of this devastating cancer. We are using a proteomic approach to test the hypothesis that changes in the amount of certain serum polypeptides, or changes in their post-translational modifications, can be used to predict the onset of HCC. Advances in the standardization of two dimensional gel electrophoresis (2DE) coupled with computerized image analysis now permit the reproducible resolution of thousands of polypeptides per run. Serum polypeptides from individuals at different stages in the disease continuum are being resolved by 2DE to identify those that change with disease progression. Polypeptides found by this method can be further characterized by mass spectrometry. In addition, the potential for changes in the glycan structure of certain polypeptides to serve as a marker for disease progression can be explored. The proteomic approach is expected to liberate us from the need to “cherry pick” or guess the best biomarkers and let the data tell us which are the best indicators of disease. Information may also be gleaned about the pathobiology of the disease process