Glycobiology and Extracellular Matrices
- Mucins and glycoproteins with mucin-like regions contain densely O-glycosylated domains often found in tandem repeat (TR) sequences. These O-glycodomains have traditionally been difficult to characterize because of their resistance to proteolytic digestion, and knowledge of the precise positions of O-glycans is particularly limited for these regions. Here, we took advantage of a recently developed glycoengineered cell-based platform for the display and production of mucin TR reporters with custom-designed O-glycosylation to characterize O-glycodomains derived from mucins and mucin-like glycoproteins.
- The human genome contains at least 35 genes that encode Golgi sulfotransferases that function in the secretory pathway, where they are involved in decorating glycosaminoglycans, glycolipids, and glycoproteins with sulfate groups. Although a number of important interactions by proteins such as selectins, galectins, and sialic acid–binding immunoglobulin-like lectins are thought to mainly rely on sulfated O-glycans, our insight into the sulfotransferases that modify these glycoproteins, and in particular GalNAc-type O-glycoproteins, is limited.
- Atrial natriuretic peptide (ANP) is a peptide hormone that in response to atrial stretch is secreted from atrial myocytes into the circulation, where it stimulates vasodilatation and natriuresis. ANP is an important biomarker of heart failure where low plasma concentrations exclude cardiac dysfunction. ANP is a member of the natriuretic peptide (NP) family, which also includes the B-type natriuretic peptide (BNP) and the C-type natriuretic peptide. The proforms of these hormones undergo processing to mature peptides, and for proBNP, this process has previously been demonstrated to be regulated by O-glycosylation.
- The GalNAc-type O-glycoproteome is orchestrated by a large family of polypeptide GalNAc-transferase isoenzymes (GalNAc-Ts) with partially overlapping contributions to the O-glycoproteome besides distinct nonredundant functions. Increasing evidence indicates that individual GalNAc-Ts co-regulate and fine-tune specific protein functions in health and disease, and deficiencies in individual GALNT genes underlie congenital diseases with distinct phenotypes. Studies of GalNAc-T specificities have mainly been performed with in vitro enzyme assays using short peptide substrates, but recently quantitative differential O-glycoproteomics of isogenic cells with and without GALNT genes has enabled a more unbiased exploration of the nonredundant contributions of individual GalNAc-Ts.
- The low-density lipoprotein receptor (LDLR) and related receptors are important for the transport of diverse biomolecules across cell membranes and barriers. Their functions are especially relevant for cholesterol homeostasis and diseases, including neurodegenerative and kidney disorders. Members of the LDLR-related protein family share LDLR class A (LA) repeats providing binding properties for lipoproteins and other biomolecules. We previously demonstrated that short linker regions between these LA repeats contain conserved O-glycan sites.
- Proteolytic processing is an irreversible post-translational modification functioning as a ubiquitous regulator of cellular activity. Protease activity is tightly regulated via control of gene expression, enzyme and substrate compartmentalization, zymogen activation, enzyme inactivation, and substrate availability. Emerging evidence suggests that proteolysis can also be regulated by substrate glycosylation and that glycosylation of individual sites on a substrate can decrease or, in rare cases, increase its sensitivity to proteolysis.
- Aberrant expression of O-glycans is a hallmark of epithelial cancers. Mucin-type O-glycosylation is initiated by a large family of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) that target different proteins and are differentially expressed in cells and organs. Here, we investigated the expression patterns of all of the GalNAc-Ts in colon cancer by analyzing transcriptomic data. We found that GalNAc-T6 was highly up-regulated in colon adenocarcinomas but absent in normal-appearing adjacent colon tissue.