Expression of an active glycosylated human gamma-glutamyl transpeptidase mutant that lacks a membrane anchor domain.

A mutant of human gamma-glutamyl transpeptidase (EC 2.3.2.2, a membrane-bound enzyme of importance in glutathione metabolism) that differs from the wild type by deletion of the putative signal peptide/anchor domain (amino acid residues 1-27) was expressed in insect cells using a baculovirus system. In contrast to the wild-type enzyme--which, as ...
expected, was mainly cell-associated--the mutant enzyme was secreted into the medium. The mutant and wild-type enzymes were purified and found to exhibit virtually identical catalytic properties. The mutant enzyme was glycosylated and processed into two subunits, as found for the wild-type enzyme. Brefeldin A inhibited secretion of the mutant enzyme and led to its accumulation in cells. The findings indicate that gamma-glutamyl transpeptidase can be targeted to the endoplasmic reticulum in a manner that does not involve function of an amino-terminal "signal/anchor" domain and that this domain is involved primarily in a membrane anchoring function. Another region of the enzyme may function as a signal domain.
Mesh Terms:
Amino Acid Sequence, Animals, Base Sequence, Cell Line, DNA Primers, Electrophoresis, Polyacrylamide Gel, Enzyme Stability, Glycoproteins, Glycosylation, Humans, Kinetics, Molecular Sequence Data, Molecular Weight, Mutagenesis, Site-Directed, Oligosaccharides, Protein Sorting Signals, Recombinant Proteins, Sequence Deletion, Spodoptera, Transfection, gamma-Glutamyltransferase
Proc. Natl. Acad. Sci. U.S.A.
Date: Jan. 03, 1995
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