Abstract: The present invention provides an isolated protein comprising a pro-domain of a proneurotrophin, methods for producing the protein, and pharmaceutical compositions containing the isolated protein. The invention also provides a nucleic acid molecule which encodes the protein and a vector containing the nucleic acid molecule. The present invention further provides a method for cleaving a proneurotrophin protein to a mature neurotrophin. In addition, the invention relates to methods for inducing apoptosis in a cell of a mammal expressing p75 surface receptors or p75 and trk receptors. The methods include causing the p75 receptor to bind a pharmaceutical composition containing a pro-domain of a proneurotrophin or administering to the mammal an effective amount of a cleavage-resistant proneurotrophin and an inhibitor of trk activation.