A 36-residue peptide contains all of the information required for 7B2-mediated activation of prohormone convertase 2

The prohormone convertases (PCs) are serine proteinases responsible for the processing of secretory protein precursors. PC2 is the only member of this family whose activation requires intracellular interaction with a helper p rotein, the neuroendocrine protein 7B2, In order to gain a better understan ding of the mechanism of proPC2 activation, we have characterized the struc tural determinants of 7B2 required for proPC2 activation. We had already id entified a proline-rich binding determinant in the 21-kDa domain, the porti on of 7B2 responsible for proPC2 activation. We have now investigated the f unction of the weakly conserved amino-terminal portion of 21-kDa 7B2 by seq uential deletions. Mutant proteins were analyzed in four assays: binding to proPC2, facilitation of proPC2 maturation, and activation of proPC2 in viv o and in vitro. We found that the aminoterminal half of 7B2 is not involved in proPC2 activation, and we identified an active 36-residue peptide that contains the previously characterized proline-rich sequence as well as an a lpha-helix and the only disulfide bond of 7B2. Mutation of the cu-helix and of the cysteines demonstrated that these determinants are absolutely requi red for PC2 activation, Thus, the 186-residue full-length 7B2 rat protein c an be functionally reduced to an internal segment of only 36 residues.