Association of prohormone convertase 3 with membrane lipid rafts

Prohormone convertase 3 (PC3) is a neuroendocrine-specific member of the su btilisin-kexin family, involved in the intracellular processing and maturat ion of prohormones and proneuropeptides. PC3 is synthesised as a proprotein that undergoes two different cleavages resulting in the mature PC3 and the enzymatically active PC3 DeltaC. In vitro translated proPC3 and proPC3 Del taC bind to trans-Golgi network (TGN)/granule-enriched membranes from the A tT20 neuroendocrine cell line in a pH-dependent manner suggesting both a do minant role for the pro-region in membrane association and that the C-termi nal region is not essential. However, while PC3 bound to membranes the majo rity of PC3 DeltaC did not, suggesting that either the pro-region or the C- terminal region of PC3 is required for membrane association. Removal of per ipheral membrane proteins did not affect the binding properties of any of t he in vitro translated proteins. Chromaffin granule membranes (CGMs) were u sed to study the binding characteristics of endogenous PC3 and its active C -terminal truncated counterpart (PC3 DeltaC). Incubation of CGMs with Trito n X-100 did not completely solubilise either of these forms of PC3. Moreove r, both PC3 and PC3 DeltaC remained associated with detergent-resistant mem brane microdomains, termed lipid rafts, purified from CGMs. The data raise the possibility that PC3 and PC3 DeltaC are sorted to the regulated secreto ry pathway via their association with membrane lipid rafts.