In the present study we describe three mutations in the binding loop of the HAI-2 Kunitz domain 1 (K42N, C47F, and R48L) that cause a delay in the SEA domain cleavage of matriptase, leading to accumulation of non-SEA domain cleaved matriptase in the ER.
We suggest that, like other known SEA domains, the matriptase SEA domain auto-cleaves and reflects that correct oligomerization, maturation, and/or folding has been obtained. Our results suggest that the HAI-2 Kunitz domain 1 mutants influence the flux of matriptase to the plasma membrane by affecting the oligomerization, maturation, and/or folding of matriptase, and as a result the SEA domain cleavage of matriptase.
Two of the HAI-2 Kunitz domain 1 mutants investigated (C47F, R48L, C47F/R48L) also displayed a reduced ability to proteolytically silence matriptase. Hence, HAI-2 separately stabilizes matriptase, regulates the secretory transport, possibly via maturation/oligomerization, and inhibits the proteolytic activity of matriptase in the ER, and possible throughout the secretory pathway.
- SEA domain cleavage
- secretory transport
- chromogenic activity