Open AccessDomain‐Specific N‐Glycosylation of the Membrane Glycoprotein Dipeptidylpeptidase IV (CD26) Influences its Subcellular Trafficking, Biological Stability, Enzyme Activity and Protein Folding
Author(s) -
Fan Hua,
Meng Wenmao,
Kilian Christiane,
Grams Sabine,
Reutter Werner
Publication year - 1997
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1997.00243.x
Subject(s) - glycosylation , dipeptidyl peptidase , asparagine , n linked glycosylation , chinese hamster ovary cell , glycoprotein , biochemistry , mutant , dipeptidyl peptidase 4 , biology , chemistry , microbiology and biotechnology , enzyme , glycan , receptor , gene , diabetes mellitus , type 2 diabetes , endocrinology
Dipeptidyl peptidase IV (DPPIV, CD26) is an N‐glycosylated type II plasma membrane protein. The primary structure of rat wild‐type DPPIV contains eight potential N‐glycosylation sites. To investigate the role of N‐glycosylation in the function of DPPIV, three of its asparagine residues were separately converted to glutamine by site‐directed mutagenesis. The resulting N‐glycosylation mutants of rat DPPIV were studied in stable transfected Chinese hamster ovary cells. All three N‐glycosylation mutants of DPPIV showed a reduced half‐life, as well as differing degrees of inhibition of the processing of their N‐glycans. Mutation of the first (Asn83→Gln) or eighth (Asn686→Gln) N‐glycosylation site had only a small effect on its enzymatic activity, cell‐surface expression and dimer formation, whereas the mutation of the sixth N‐glycosylation site (Asn319→Gln) abolished the enzymatic activity, eliminated cell‐surface expression and prevented the dimerization of the DPPIV protein. The mutant [Gln319]DPPIV is retained in the cytoplasm and its degration was drastically increased. Our data suggest that the N‐glycosylation at Asn319 is involved in protein trafficking and correct protein folding.