Title : The O-glycomap of
lubricin , a novel
mucin responsible for joint lubrication, identified by site-specific
glycopeptide analysis
Abstract :
- The lubricative, heavily glycosylated mucin-like synovial glycoprotein lubricin has previously been observed to contain glycosylation changes related to rheumatoid and osteoarthritis
- Thus, a site-specific investigation of the glycosylation of lubricin was undertaken, in order to further understand the pathological mechanisms involved in these diseases
- Lubricin contains an serine/threonine/proline ( STP )-rich domain composed of imperfect tandem repeats (EPAPTTPK), the target for O-glycosylation
- In this study, using a liquid chromatography-tandem mass spectrometry approach, employing both collision-induced and electron-transfer dissociation fragmentation methods, we identified 185 O-glycopeptides within the STP-rich domain of human synovial lubricin
- This showed that adjacent threonine residues within the central STP-rich region could be simultaneously and/or individually glycosylated
- In addition to core 1 structures responsible for biolubrication, core 2 O-glycopeptides were also identified, indicating that lubricin glycosylation may have other roles
- Investigation of the expression of polypeptide N-acetylgalactosaminyltransferase genes was carried out using cultured primary fibroblast-like synoviocytes, a cell type that expresses lubricin in vivo
- This analysis showed high mRNA expression levels of the less understood polypeptide N-acetylgalactosaminyltransferase 15 and 5 in addition to the ubiquitously expressed polypeptide N-acetylgalactosaminyltransferase 1 and 2 genes
- This suggests that there is a unique combination of transferase genes important for the O-glycosylation of lubricin
- The site-specific glycopeptide analysis covered 82% of the protein sequence and showed that lubricin glycosylation displays both micro- and macroheterogeneity
- The density of glycosylation was shown to be high: 168 sites of O-glycosylation, predominately sialylated, were identified
- These glycosylation sites were focused in the central STP-rich region , giving the domain a negative charge
- The more positively charged lysine and arginine residues in the N and C termini suggest that synovial lubricin exists as an amphoteric molecule
- The identification of these unique properties of lubricin may provide insight into the important low-friction lubricating functions of lubricin during natural joint movement
Output (sent_index, trigger,
protein,
sugar,
site):
- 0. glycopeptide, , -, -, glycopeptide
- 1. glycoprotein, , glycoprotein, -, -
- 10. glycopeptide, , -, -, glycopeptide
- 11. O-glycosylation, , -, -, sites
- 11. sialylated, , -, -, sites
- 12. glycosylation, , -, -, sites
- 2. glycosylation, , lubricin, -, -
- 4. O-glycopeptides, , -, -, O-glycopeptides
- 5. glycosylated, , -, -, threonine residues
- 9. O-glycosylation, , lubricin, -, -
Output(Part-Of) (sent_index,
protein,
site):
- 12. STP, region
- 3. Lubricin, domain
- 4. STP, domain
- 4. lubricin, domain
- 5. STP, region
*Output_Site_Fusion* (sent_index,
protein,
sugar,
site):