Posttranslational removal of the carboxyl-terminal KDEL of the cysteine protease SH-EP occurs prior to maturation of the enzyme

Takashi Okomoto, Takao Minamikawa, Gerald Edward, Vikram Vakharia, Eliot M Herman

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SH-EP is a cysteine protease from germinating mung bean (Vigna mungo) that possesses a carboxyl-terminal endoplasmic reticulum (ER) retention sequence, KDEL. In order to examine the function of the ER retention sequence, we expressed a full-length cDNA of SH-EP and a minus-KDEL control in insect Sf-9 cells using the baculovirus system. Our observations on the synthesis, processing, and trafficking of SH-EP in Sf-9 cells suggest that the KDEL ER-retention sequence is posttranslationally removed either while the protein is still in the ER or immediately after its exit from the ER, resulting in the accumulation of proSH-EP minus its KDEL signal. It is this intermediate form that appears to progress through the endomembrane system and is subsequently processed to form mature active SH-EP. The removal of an ER retention may regulate protein delivery to a functional site and present an alternative role for ER retention sequences in addition to their well established role in maintaining the protein composition of the ER lumen.

Original languageEnglish (US)
Pages (from-to)11390-11398
Number of pages9
JournalJournal of Biological Chemistry
Issue number16
Publication statusPublished - Apr 16 1999
Externally publishedYes


ASJC Scopus subject areas

  • Biochemistry

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