Influence of Ca2+ and pH on the folding of the prourotensin II precursor

Abstract

Proper folding is a crucial step for the trafficking of proteins through the secretory pathway. We hypothesized that the secretory granules of endocrine cells provide optimal folding conditions of prohormone precursors for cleavage. Here, using circular dichroism and in vitro processing on purified prourotensin II (ProUII), we show that the precursor undergoes pH- and Ca(2+)-dependent conformational and stability changes. ProUII has a stable tertiary structure at pH 5.5 in presence of Ca(2+) and is correctly cleaved in these conditions by prohormone convertases. Taken together, our results support the notion that precursors may need to be optimally folded in the lumen of secretory granules for their processing.