Posttranslational removal of the carboxyl-terminal KDEL of the cysteine protease SH-EP occurs prior to maturation of the enzyme.
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.
Okamoto
T
T
Department of Biological Sciences, Tokyo Metropolitan University, Minami-osawa, Hachioji, Tokyo, 192-0397 Japan. okamoto-takashi@c.metro-u.ac.jp
Minamikawa
T
T
Edward
G
G
Vakharia
V
V
Herman
E
E
Okomoto
T
T
D000818:Animals; D001483:Base Sequence; D018548:Cotyledon / Q000201:enzymology; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D018076:DNA, Complementary; D007150:Immunohistochemistry; D016253:Microscopy, Immunoelectron; D009842:Oligopeptides / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D018411:Spodoptera; D013347:Subcellular Fractions / Q000201:enzymology
D017931:DNA Primers; D018076:DNA, Complementary; D009842:Oligopeptides; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; C073762:lysyl-aspartyl-glutamyl-leucine; D003546:Cysteine Endopeptidases; C095010:processing enzyme 1, Vigna mungo