Lubricin is a mucin like glycoprotein with extensive O-linked glycosylation. The abundance of negatively charged glycans of lubricin contributes to the proteins boundary lubrication

of the cartilage surface due to strong repulsive hydration forces [28,29,30,31]. During inflammation, the glycosylation properties such as sialylation, fucosylation and sulfation are regulated to manipulate cell adhesion, differentiation, maturation and activation in the case of immune cells. The literature [28,32] suggests that glycosidases such as galactosidases and neuraminidases significantly reduce the lubricating property of lubricin. Before incubation with sialidase Inhibitors,research,lifescience,medical S, the MS2 spectral intensity of the sialylated structure gave an indecisive result when compared with spectra reported in the MS2 database UniCarb-DB. The incubation of human synovial lubricin with sialidase S indicates the degradation of mono-sialylated core 1 and mono- Inhibitors,research,lifescience,medical and Selleckchem PF2341066 di-sialylated core 2 structures (Figure 2b), which is accompanied Inhibitors,research,lifescience,medical by an increase

in the intensity of the neutral structures generated by the removal of sialic acid (Figure 2b). The MS2 spectral intensity correlation with spectra reported in the MS2 database UniCarb-DB helped in assigning the structure created by the removal of sialic acid, while the degradation of these mono-sialylated core 1 and mono- and di-sialylated core 2 structures are terminated by α2-3 Inhibitors,research,lifescience,medical –linked sialic acid. The exoglycosidase digestion specific to

sialic acid and a MS2 spectral library comparison minimized the use of time-consuming exoglycosidase digestion to monosaccharide unit for structural assignment. This degradation suggested that Inhibitors,research,lifescience,medical these mono-sialylated core 1 and mono- and di-sialylated core 2 structures are terminated by α2-3 –linked sialic acid. Having shown that exoglycosidase digestion of human synovial lubricin oligosaccharides and a MS2 spectral library comparison can provide information about assignment of individual structures present in the sample, we extended our analysis into addressing the assignment of the non-digestible terminal HexNAc configuration present in PGM oligosaccharides using MS3. This suggested that the non-digestable PDK4 terminal HexNAc in PGM oligosaccharides may be the antibacterial terminal α1,4 linked GlcNAc epitope. In order to address the exoglycosidase activity of saliva we proposed that saliva is capable of digesting mucin oligosaccharides still attached to mucins blotted onto pvdf membranes. The human oral cavity sustains the growth of more than 500 different strains of bacteria [33] of which both harmful and beneficial bacteria use the oligosaccharide chains of mucins as a nutrient source [34].