THE C-TYPE LECTIN DOMAINS OF LECTICANS, A FAMILY OF AGGREGATING CHONDROITIN SULFATE PROTEOGLYCANS, BIND TENASCIN-R BY PROTEIN-PROTEIN INTERACTIONS INDEPENDENT OF CARBOHYDRATE MOIETY

The lecticans are a family of chondroitin sulfate proteoglycans includ ing aggrecan, versican, neurocan, and brevican. The C-terminal globula r domains of lecticans are structurally related to selectins, consisti ng of a C-type lectin domain flanked by epidermal growth factor and co mplement regulatory protein domains, The C-type lectin domain of versi can has been shown to bind tenascin-R, an extracellular matrix protein specifically expressed in the nervous system, and the interaction was presumed to be mediated by a carbohydrate-protein interaction. In thi s paper, we show that the C-type lectin domain of brevican, another le ctican that is specifically expressed in the nervous system, also bind s tenascin-R Surprisingly, this interaction is mediated by a protein-p rotein interaction through the fibronectin type III domains 3-5 of ten ascin-R, independent of any carbohydrates or sulfated amino acids, The lectin domains of versican and other lecticans also bind the same dom ain of tenascin a by protein-protein interactions, Surface plasmon res onance analysis revealed that brevican lectin has at least a 10-fold h igher affinity than the other lectican lectins, Tenascin-R is coprecip itated with brevican from adult rat brain extracts, suggesting that te nascin-R and brevican form complexes in vivo, These results demonstrat e that the C-type lectin domain can interact with fibronectin type III domains through protein-protein interactions, and suggest that brevic an is a physiological tenascin-R ligand in the adult brain.