Release segments and binding compositions comprising same

The present invention relates to activatable recombinant polypeptide compositions comprising a cleavage release segment. In some instances, the activatable recombinant polypeptide compositions include an XTEN linked to binding moieties by cleavable release segments that, when cleaved, the binding moieties are capable of binding together effector T cells with targeted tumor or cancer cells and effecting cytolysis of the tumor cells or cancer cells. The invention also provides compositions and methods of making and using the cleavable activatable recombinant compositions.