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Characterization of rat cathepsin E and mutants with changed active‐site residues and lacking propeptides and N‐glycosylation, expressed in human embryonic kidney 293T cells
Author(s) -
Tsukuba Takayuki,
Ikeda Shinobu,
Okamoto Kuniaki,
Yasuda Yoshiyuki,
Sakai Eiko,
Kadowaki Tomoko,
Sakai Hideaki,
Yamamoto Kenji
Publication year - 2006
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2005.05062.x
Subject(s) - protein precursor , endoplasmic reticulum , glycosylation , endosome , cathepsin e , kdel , biochemistry , cathepsin c , golgi apparatus , mutant , cathepsin d , brefeldin a , biology , n linked glycosylation , endoplasmic reticulum associated protein degradation , tunicamycin , furin , lysosome , cathepsin l , microbiology and biotechnology , cathepsin , cathepsin o , intracellular , unfolded protein response , glycoprotein , enzyme , gene , glycan
To study the roles of the catalytic activity, propeptide, and N‐glycosylation of the intracellular aspartic proteinase cathepsin E in biosynthesis, processing, and intracellular trafficking, we constructed various rat cathepsin E mutants in which active‐site Asp residues were changed to Ala or which lacked propeptides and N‐glycosylation. Wild‐type cathepsin E expressed in human embryonic kidney 293T cells was mainly found in the LAMP‐1‐positive endosomal organelles, as determined by immunofluorescence microscopy. Consistently, pulse–chase analysis revealed that the initially synthesized pro‐cathepsin E was processed to the mature enzyme within a 24 h chase. This process was completely inhibited by brefeldin A and bafilomycin A, indicating its transport from the endoplasmic reticulum (ER) to the endosomal acidic compartment. Mutants with Asp residues in the two active‐site consensus motifs changed to Ala and lacking the propeptide (Leu23‐Phe58) and the putative ER‐retention sequence (Ser59‐Asp98) were neither processed nor transported to the endosomal compartment. The mutant lacking the ER‐retention sequence was rapidly degraded in the ER, indicating the importance of this sequence in correct folding. The single (N92Q or N324D) and double (N92Q/N324D) N‐glycosylation‐deficient mutants were neither processed into a mature form nor transported to the endosomal compartment, but were stably retained in the ER without degradation. These data indicate that the catalytic activity, propeptides, and N‐glycosylation of this protein are all essential for its processing, maturation, and trafficking.