title: Opticin binds to heparan and chondroitin sulfate proteoglycans.
abstract: OBJECTIVE
  The extracellular matrix glycoprotein opticin is a small leucine-rich repeat proteoglycan/protein family member that was discovered associated with vitreous humor collagen fibrils. Opticin is present throughout the vitreous, but is particularly concentrated at the internal limiting lamina, where it colocalizes with type XVIII collagen. The present study investigated whether opticin interacts directly with the heparan sulfate (HS) proteoglycan type XVIII collagen.
  
  
  METHODS
  Solid-phase opticin binding assays were performed with immobilized type XVIII collagen and heparin albumin. Surface plasmon resonance (SPR) was used to investigate the binding of opticin to heparin and HS.
  
  
  RESULTS
  Opticin bound to type XVIII collagen via its HS chains. SPR showed that opticin bound to porcine intestinal mucosa HS and heparin with moderately high affinity (K(D) 73 and 43 nM, respectively). Binding inhibition studies showed that hexasaccharides of heparin had a lower affinity for opticin than larger oligosaccharides; the sulfate groups of heparin contributed variably to opticin binding, with the group at ring position two of iduronate contributing least; and chondroitin sulfate A and B bound to opticin, whereas binding to chondroitin sulfate C and hyaluronan was not observed.
  
  
  CONCLUSIONS
  Opticin binds to heparin, HS, chondroitin 4-sulfate, and dermatan sulfate, the binding affinity being dependent on sulfation pattern and oligosaccharide chain length. Opticin may provide a link between cortical vitreous collagen fibrils and the inner limiting lamina by binding HS proteoglycans and stabilize vitreous gel structure by binding chondroitin sulfate proteoglycans.
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences and Academic Unit of Eye & Vision Science, School of Medicine, University of Manchester, United Kingdom.
authors.forename: V John
authors.initials: VJ
authors.lastname: Hindson
authors.forename: John T
authors.initials: JT
authors.lastname: Gallagher
authors.forename: Willi
authors.initials: W
authors.lastname: Halfter
authors.forename: Paul N
authors.initials: PN
authors.lastname: Bishop
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D011508:Chondroitin Sulfate Proteoglycans / Q000378:metabolism*; D043170:Collagen Type XVIII / Q000378:metabolism*; D016326:Extracellular Matrix Proteins; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism*; D011485:Protein Binding; D011509:Proteoglycans; D011817:Rabbits
chemical_list: D011508:Chondroitin Sulfate Proteoglycans; D043170:Collagen Type XVIII; D016326:Extracellular Matrix Proteins; D019812:Heparan Sulfate Proteoglycans; C404108:OPTC protein, human; D011509:Proteoglycans