THE FUNCTION AND DIFFERENTIAL SORTING OF A FAMILY OF APLYSIA PROHORMONE PROCESSING ENZYMES

We have cloned four members of the family of subtilisin-like endoproteases expressed in the bag cell neurons of Aplysia and have demonstrated that two of these enzymes are capable of correctly cleaving the egg-laying hormone precursor. The egg-laying hormone precursor undergoes an ordered series of cleavages, such that different peptides are differentially sorted into distinct secretory vesicles. We have used electron microscopic chemistry to demonstrate that at least one processing enzyme is differentially segregated into a class of secretory vesicles containing the bag cell peptides. The segregation of specific endoproteases, along with specific neuropeptides within a given cell type, may ensure appropriate cleavage and prevent inappropriate cleavage of the polyprotein precursors.