Abstract
The proprotein convertase 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. 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 zymogen proprotein convertases, all incompletely matured intermediates of SKI-1/S1P showed full catalytic activity toward cellular substrates, whereas optimal cleavage of viral glycoproteins depended on B'/B processing. Incompletely matured 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 toward cellular and pathogen-derived substrates.
Highlights
Zymogen activation of proprotein convertases requires excision of their prodomain for activity
WT and ⌬AC subtilisin kexin isozyme 1 (SKI-1)/ site 1 protease (S1P) FL were expressed in the SKI-I/S1P-deficient CHO cell line SRD12B, which lacks active endogenous enzyme [21], and recombinant SKI-1/S1P autoprocessing was analyzed by Western blotting
⌬AC SKI-1/S1P, which was present as a single form, was sensitive to both Endo H and PNGase F, suggesting that the protein does not traffic beyond the ER (Fig. 1B)
Summary
Zymogen activation of proprotein convertases requires excision of their prodomain for activity. Results: SKI-1/S1P matures into a plethora of forms that retain prodomain fragments and are active in different subcellular compartments. The proprotein convertase 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. In contrast to other zymogen proprotein convertases, all incompletely matured intermediates of SKI-1/S1P showed full catalytic activity toward cellular substrates, whereas optimal cleavage of viral glycoproteins depended on B/B processing. Matured forms of SKI-1/S1P further process cellular and viral substrates in distinct subcellular compartments. Our study reveals novel and unexpected features of SKI-1/S1P zymogen activation and subcellular specificity of activity toward cellular and pathogen-derived substrates. We investigated SKI-1/S1P zymogen activation and subcellular specificity of activity toward cellular and pathogen-derived substrates revealing novel and unexpected features
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