Characterization of fibrosurfin, an interfibrillar component of sea urchincatch connective tissues

The Sea URchin Fibrillar (SURF) domain is a four-cysteine module present in the amino-propeptide of the sea urchin 2 alpha fibrillar collagen chain. D espite numerous international genome and expressed sequence tag projects, c omputer searches have so far failed to identify similar domains in other sp ecies. Here, we have characterized a new sea urchin protein of 2656 amino a cids made up of a series of epidermal growth factor-like and SURF modules. From its striking similarity to the modular organization of fibropellins, w e called this new protein fibrosurfin. This protein is acidic with a calcul ated pi of 4.12, Eleven of the 17 epidermal growth factor-like domains corr espond to the consensus sequence of calcium-binding type. By Western blot a nd immunofluorescence analyses, this protein is not detectable during embry ogenesis, In adult tissues, fibrosurfin is colocalized with the amino-prope ptide of the 2 alpha fibrillar collagen chain in several collagenous ligame nts, i.e., test sutures, spine ligaments, peristomial membrane, and to a le sser extent, tube feet. Finally, immunogold labeling indicates that fibrosu rfin is an interfibrillar component of collagenous tissues. Taken together, the data suggest that proteins possessing SURF modules are localized in th e vicinity of mineralized tissues and could be responsible for the unique p roperties of sea urchin mutable collagenous tissues.