Sorting of the vasopressin prohormone into the regulated secretory pathway

The sorting of soluble proteins into the regulated secretory pathway (RSP) involves aggregation, but whether an additional sorting domain is also requ ired is not clear. By fusing vasopressin prohormone (proVP) fragments to gr een fluorescent protein (eGFP) me have determined whether a sorting domain can function independently of the aggregative neurophysin domain. Although eGFP itself can be immunolocalised in the RSP of Neuro2A and AtT20 cells, m ost of the protein enters the constitutive pathway, and is found in the cul ture medium. In contrast, the N-terminal 27 residues of proVP promote resid ence in the RSP, Furthermore, only the processed form of this fusion was se creted when stimulated. We suggest a sorting mechanism based on the recogni tion of a sorting motif, the efficiency of which is enhanced by neurophysin aggregation, (C) 2000 Federation of European Biochemical Societies. Publis hed by Elsevier Science B.V. All rights reserved.