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

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