Abstract
Prohormone convertase 1 (PC1) was previously characterized as a partially transmembrane protein in purified chromaffin granules of bovine adrenal medulla1. This was challenged with experiments on transfected PC1 in COS1 cells, a non-endocrine cell line2. To address this issue, we undertook to analyze its extraction properties in vitro and its immunocytochemical localization in situ in AtT20 cells, an endocrine cell line that expresses PC1. Most of the 87 kDa form of PC1 was resistant to carbonate extraction suggesting that it had properties of a transmembrane protein. Under semi-permeabilized conditions whereby only the plasma membrane was permeabilized, the carboxy-terminus of PC1 was specifically immunostained whereas the amino-terminus was not. These results indicate that the amino-terminus of PC1 was within the lumen of the Golgi and granules, and some of the C-terminus was exposed to the cytosol. Thus, endogenous PC1 can assume a transmembrane orientation in situ in AtT20 cells.
Highlights
The proprotein convertases (PCs) belong to a family of endoproteinases that cleave proproteins at basic residue cleavage sites[3]
It was found that the 64 kDa form of Prohormone convertase 1 (PC1) was predominantly recovered in the phosphate buffered saline (PBS) supernatant whereas the 87 kDa form was recovered in the PBS pellet
Prohormone convertase 1 (PC1) is sorted to the regulated secretory pathway (RSP) ofendocrine cells where it functions to cleave prohormones and proneuropeptides into smaller peptides that function in important biological processes
Summary
The proprotein convertases (PCs) belong to a family of endoproteinases that cleave proproteins at basic residue cleavage sites[3]. Homologous to furin were subsequently cloned, of which PC1 ( described as PC3 or SPC3) and PC2 were found to be exclusively expressed in (neuro) endocrine tissue[10,11,12,13,14], suggesting their function to be specific for the maturation of peptide hormones and neuropeptides. Both enzymes do not contain classical amino acid sequences that would predict them to have a transmembrane domain. Recent studies by Dikeakos et al.[27,28], have characterized by NMR the extreme C-terminal sequence and identified important residues within the sequence involved in binding to membrane patches which were important for sorting
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
