Zymogen Activation and Subcellular Activity of Subtilisin Kexin Isozyme-1/Site-1 Protease [Cell Biology]

November 10th, 2014 by Ramos da Palma, J., Burri, D. J., Oppliger, J., Salamina, M., Cendron, L., Polverino de Laureto, P., Seidah, N. G., Kunz, S., Pasquato, A.

The proprotein convertase (PC) subtilisin kexin isozyme-1 (SKI-1)/site-1 protease (S1P) plays crucial roles in cellular homeostatic functions and is hijacked by pathogenic viruses for the processing of their envelope glycoproteins (GPs). Zymogen activation of SKI-1/S1P involves sequential autocatalytic processing of its N-terminal prodomain at sites B'/B followed by the herein newly identified C'/C sites. We found that SKI-1/S1P autoprocessing results in intermediates whose catalytic domain remains associated with prodomain fragments of different lengths. In contrast to other PCs, all immature intermediates of SKI-1/S1P showed full catalytic activity towards cellular substrates, whereas optimal cleavage of viral GPs depended on B'/B processing. Immature forms of SKI-1/S1P further process cellular and viral substrates in distinct subcellular compartments. Using a cell-based sensor for SKI-1/S1P activity, we found that 9 amino acid residues at the cleavage site (P1-P8) and P1' are necessary and sufficient to define the subcellular location of processing and to determine to what extent processing of a substrate depends on SKI-1/S1P maturation. In sum, our study reveals novel and unexpected features of SKI-1/S1P zymogen activation and subcellular specificity of activity towards cellular and pathogen-derived substrates.