- The cysteine-rich domain of the secreted proprotein convertases PC5A and PACE4 functions as a cell surface anchor and interacts with tissue inhibitors of metalloproteinases. Nour, N., Mayer, G., Mort, J.S., Salvas, A., Mbikay, M., Morrison, C.J., Overall, C.M., Seidah, N.G. Mol. Biol. Cell (2005)