In particular, the present invention provides polypeptides comprising the amino acid sequence of residues n-468 of SEQ ID NO:2, where n is an integer in the range of 24-132 where C-132 is the first residue from the N-terminus of the extracellular domain of the DR4 polypeptide (shown in SEQ ID NO:2) believed to be required for receptor-ligand binding (e.g., TRAIL binding) activity of the DR4 protei