No abstract

Protein glycosylation is a critical subject attracting increasing attention in the field of proteomics as it is expected to play a key role in the investigation of histological and diagnostic biomarkers. In this context, an enormous number of glycoproteins have now been nominated as disease-related biomarkers. However, there is no appropriate strategy in the current proteome platform to qualify such marker candidate molecules, which relates their specific expression to particular diseases. Here, we present a new practical system for focused differential glycan analysis in terms of antibody-assisted lectin profiling (ALP). In the developed procedure, (i) a target protein is enriched from clinic samples (e.g. tissue extracts, cell supernatants, or sera) by immunoprecipitation with a specific antibody recognizing a core protein moiety; (ii) the target glycoprotein is quantified by immunoblotting using the same antibody used in (i); and (iii) glycosylation difference is analyzed by means of antibody-overlay lectin microarray, an application technique of an emerging glycan profiling microarray. As model glycoproteins having either N-linked or O-linked glycans, prostate-specific antigen or podoplanin, respectively, were subjected to systematic ALP analysis. As a result, specific signals corresponding to the target glycoprotein glycans were obtained at a sub-picomole level with the aid of specific antibodies, whereby disease-specific or tissue-specific glycosylation changes could be observed in a rapid, reproducible, and highthroughput manner. Thus, the established system should provide a powerful pipeline in support of ongoing efforts in glyco-biomarker discovery. Molecular & Cellular Proteomics 8:99 -108, 2009.

Podoplanin (Aggrus) is a mucin-type sialoglycoprotein that plays a key role in tumor cell-induced platelet aggregation. Podoplanin possesses a platelet aggregation-stimulating (PLAG) domain, and Thr52 in the PLAG domain of human podoplanin is important for its activity. Endogenous or recombinant human podoplanin were purified, and total glycosylation profiles were surveyed by lectin microarray. Analyses of glycopeptides produced by Edman degradation and mass spectrometry revealed that the disialyl-corel (NeuAca2-3Galbl-3(NeuAca2-6)GalNAcal-O-Thr) structure was primarily attached to a glycosylation site at residue Thr52. Sialic acid-deficient podoplanin recovered its activity after additional sialylation. These results indicated that the sialylated Corel at Thr52 is critical for podoplanin-induced platelet aggregation.

Chlamydia trachomatis LGV-434 was grown in HeLa 229 cells. Benzylpenicillin completely inhibited the formation of infectious elementary bodies (EBs) at a concentration of 19 pmol/ml or higher and produced abnormally large reticulate bodies (RBs) in the inclusions at 30 pmol/ml or higher. The possible targets for penicillin in C. trachomatis were three penicillin-binding proteins (PBPs) which were identified in the Sarkosyl-soluble fractions of both RBs and EBs. The apparent subunit molecular weights were 88,000 (PBP 1), 61,000 (PBP 2), and 36,000 (PBP 3). The 50% binding concentrations of [3H]penicillin for PBPs 1 to 3 in EBs and RBs were between 7 and 70 pmol/ml. Such high susceptibility to penicillin was shown by an organism that did not have detectable muramic acid (<0.02% by weight) in preparations of either whole cells or sodium dodecyl sulfate-insoluble residues.

Mucin-type O-glycans are the most typical O-glycans found in mammalian cells and assume many different biological roles. Here, we report a genetic engineered yeast strain capable of producing mucintype sugar chains. Genes encoding Bacillus subtilis UDP-Gal/GalNAc 4-epimerase, human UDP-Gal/GalNAc transporter, human ppGalNAc-T1, and Drosophila melanogaster core1 ␤1-3 GalT were introduced into Saccharomyces cerevisiae. The engineered yeast was able to produce a MUC1a peptide containing O-glycan and also a mucin-like glycoprotein, human podoplanin (hPod; also known as aggrus), which is a platelet-aggregating factor that requires a sialyl-core1 structure for activity. After in vitro sialylation, hPod from yeast could induce platelet aggregation. Interestingly, substitution of ppGalNAc-T1 for ppGalNAc-T3 caused a loss of platelet aggregation-inducing activity, despite the fact that the sialyl-core1 was detectable in both hPod proteins on a lectin microarray. Most of O-mannosylation, a common modification in yeast, to MUC1a was suppressed by the addition of a rhodanine-3-acetic acid derivative in the culture medium. The yeast system we describe here is able to produce glycoproteins modified at different glycosylation sites and has the potential for use in basic research and pharmaceutical applications.glycosylation engineering ͉ mucin-type glycan ͉ podoplanin M ucin-type glycosylation is one of the most abundant posttranslational modifications. The modification is initiated by O-linked N-acetylgalactosamine (GalNAc) to Ser or Thr residues on a peptide backbone and is involved in a variety of important biological processes, such as processing of hormones (1), endocytosis (2), and sorting of apical proteins in the Drosophila embryo (3). Mucin-type glycans are sometimes clustered, forming the ''mucin domain'' found on both membrane-bound (4) and secreted mucins (5), which function as a selective molecular barrier at the epithelial surface (6) and are involved in morphogenetic signal transduction (7). It is also known that changes in expression of mucin and in their glycosylation state are closely associated with the development of cancer and cancer-related processes such as cell growth, differentiation, adhesion, invasion, and immune surveillance (8). Immunohistochemical studies have identified several tumor-associated antigens (TAAs) of adenocarcinoma (9), and most TAAs on mucins were originally found as sialylated mucin-type glycans (10). Podoplanin (also called aggrus) (11, 12), one of mucin-type glycoproteins, acts as a platelet-aggregating factor for cancer cells, a finding that has attracted recent attention because it is well known that the platelet-aggregating activity of cancer cells influences tumor metastasis. In fact, the anti-human podoplanin antibody NZ-1 has an inhibitory effect on lung colonization of human podoplanintransfected cells (13). Additionally, podoplanin is a potential diagnostic marker for many tumors, including testicular tumors, several squamous cell carcinomas, and brain tumors, and may be ...