In a cell free system , binding of a protein fragment ( 175 475 ) bound to __NODE__ and containing a ligand binding domain from __SP__ __NODE__ protein and a protein fragment ( 747 974 ) from __SP__ __NODE__ protein is greater than binding of a protein fragment ( 1 472 ) from __SP__ __NODE__ protein and a protein fragment ( 175 475 ) bound to __NODE__ and containing a ligand binding domain from __SP__ __NODE__ protein .