MULTIPLE LAMININ-BINDING PROTEINS IN HUMAN FETAL HEART

The possibility of occurrence of laminin binding proteins in cardiac t issue under different stages of growth was examined by affinity chroma tography of the soluble fraction of human fetal myocardial plasma memb rane over Ln-Sepharose. A 67 kDa protein was isolated by elution with glycine/HCl buffer containing 1 M NaCl and visualized as a coomassie s tainable band on SDS gel electrophoresis under reducing conditions. Do t blot assays of the radioiodinated protein revealed the binding of 67 kDa protein with high affinity to laminin in a cation independent man ner. This protein appears to be present in relatively higher amounts i n tissues from early stage fetus. The occurrence of cation dependent l aminin binding poteins was also examined by affinity chromatography. E lectrophoresis of the EDTA eluate under reducing conditions followed b y silver staining showed two prominent bands with average molecular si ze 130 and 174 kDa which under non-reducing conditions appeared as two bands with average molecular weight of 115 and 135 kDa. Using radioio dinated protein in dot blot assays, its binding to Ln was found to be maximum in the presence of Mn++ ions. Immunoblotting using anti-beta(1 ) integrin antibodies showed that 115 kDa protein is a beta(1) integri n suggesting the possibility of this protein belonging to the integrin group of receptors. The occurrence of multiple laminin binding protei ns and the relative abundance of one of these proteins viz. the 67 kDa protein during early stages than in late stage tussue suggest a possi ble role for these proteins in cellular interactions with laminin duri ng myocardial tissue development.