br Structure The presence of glycans

Structure The presence of glycans on collagens has been first described in 1935, when Grassmann and Schleich assigned up to 1% of the mass of collagen to JWH 133 sale [4]. Twenty years later, these carbohydrates were determined to be bound to the polypeptide chains through O-glycosidic linkages [5]. In the late 1960s, Robert and Mary Jane Spiro determined the structure of the collagen O-glycan [] and characterized the glycosyltransferase enzymes involved in its biosynthesis [7,8]. In their seminal work, they described the O-glycan as a simple disaccharide of glucose and galactose linked to Hyl. Despite its simplicity, the Glc(α1-2)Gal(β1-O) sequence (Figure 2) is unique among glycoconjugates. The collagen disaccharide is also remarkable in respect to its strict conservation among animals expressing collagens, from sponges to humans. The extent of glycosylation varies according to the types of collagen, with collagen type IV being more extensively glycosylated than collagen type II and collagen type I. In general, glycosylation of Hyl is more prominent in basement membrane collagens than in fibrillar collagens. The extent of collagen glycosylation probably depends on the speed of collagen folding, the expression levels of glycosyltransferases, and UDP-Gal availability in the ER compartment. Collagen type IV is the main constituent of basement membranes. It does not form fibrils but oligomerizes at its N-terminus with other collagen IV molecules for form tetramers and at its C-terminus to form dimers. Mouse collagen type IV isolated from Engelbreth-Holm-Swarm tumor cells was shown to contain 39 glycosylated Hyl residues, whereas additional 10 Hyl were detected without glycans [9]. Its C-terminus, which initiates the helical polymerization process, lacks post-translational modifications. Bovine collagen type II, a fibrillar collagen mainly found in cartilage, comprises 24 potentially glycosylated lysine residues within its collagen domain. Detailed analysis revealed that 22 out of 23 of these lysine residues are hydroxylated and carry variable numbers of Gal(β1-O) and Glc(α1-2)Gal(β1-O) glycans. The extent of glycosylation of individual lysine residues was found to be highly variable, with the position of lysine along the polypeptide as a key determinant of glycosylation efficiency. For example, K884 was glycosylated at more than 95% whereas K956 was only glycosylated at less than 5% [10]. The mapping of glycosylation sites in other collagen types, such as bovine collagen type V also revealed a majority of glycosylated Lysine residues, with 34 glycosylated Hyl sites and only 3 unmodified Hyl sites in bovine placenta COL5A1 [11]. Another study of embryonic calf skin collagen type V identified 39 Hyl on COL5A1 and 22 Hyl on COL5A2. All of the Hyl sites on COL5A1 were glycosylated with 85% Glc(α1-2)Gal(β1-O) and 15% Gal(β1-O), whereas the 22 sites on COL5A2 were less glycosylated with only 55% carrying the disaccharide Glc(α1-2)Gal(β1-O) and 45% Gal(β1-O) [12].