Functional expression in Aspergillus oryzae of p15, a protein with potent neurite-inducing activity in PC12 cells

We previously reported that a fungal protein, p15, induces neurite outgrowth and differentiation of rat pheochromocytoma PC12 cells through the activation of the Ca2+ signaling pathway. We report here the secretory production of p15 in Aspergillus oryzae. Analysis of culture supernatant of A. oryzae transformed with the gene encoding the p15 precursor tagged with a hemagglutinin (HA) epitope demonstrated that the transformant secreted a protein with an apparent molecular mass of 17.5 kDa, which is a little larger than the expected size of mature p15-HA. By heat denaturation and ion exchange chromatography, p15-HA was easily purified from the culture supernatant with sufficient abundance. Although purified p15-HA was less active than the native p15 obtained from the culture broth of a producing fungal strain, it had neurite-inducing activity in PC12 cells in a dose-dependent manner, providing a system to study the action mechanism of p15.