A defective cell surface collagen-binding protein in dermatosparactic sheep fibroblasts

Fibroblasts from dermatosparactic sheep fail to contract collagen gels and show a reduced attachment to collagenous substrates. By comparing collagen-binding membrane proteins of normal (+/+), homozygote (-/-), and heterozygote (+/-) fibroblasts, we present evidence that the interaction of normal fibroblasts with native type I collagen involves a protein of apparent Mr = 34,000 which is absent from dermatosparactic fibroblasts and seems to be related to anchorin CII. This conclusion was reached from the following experiments: (a) On a blot of membrane proteins from normal fibroblasts radioactively labeled type I collagen bound predominantly to a protein band of 34 kD; dermatosparactic membranes revealed only a small amount of binding to a component with a molecular mass of 47 kD. (b) After separation of normal fibroblast membrane proteins on type I collagen-Sepharose, a collagen-binding component of 34 kD was found which was absent from the corresponding fraction of dermatosparactic membranes. (c) Antibodies to anchorin CII stained the surface of normal (+/+), but not of dermatosparactic (-/-) fibroblasts and labeled a 34-kD component after immunoblotting of normal fibroblast membrane proteins. (d) After metabolic labeling of fibroblasts with [35S]methionine and immunoprecipitation with anti-anchorin CII, 40- and 34-kD components were precipitated from extracts of normal fibroblasts, while the latter component was absent from affected cells. Similar differences were found after immunoblotting of membranes from whole normal or affected skin. These data indicate that dermatosparaxis of sheep involves a molecular defect of a collagen-binding protein. Therefore this disease represents a model to study the complex interaction of cells with the extracellular matrix on a molecular level.