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N-glycosylation of carnosinase influences protein secretion and enzyme activity: implications for hyperglycemia

The (CTG)n polymorphism in the serum carnosinase (CN-1) gene affects CN-1 secretion. Since CN-1 is heavily glycosylated and glycosylation might influence protein secretion as well, we tested the role of N-glycosylation for CN-1 secretion and enzyme activity. We also tested whether CN-1 secretion is...

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Main Authors: Riedl, Eva (Author) , Köppel, Hannes (Author) , Pfister, Frederick (Author) , Peters, Verena (Author) , Hauske, Sibylle J. (Author) , Sternik, Paula (Author) , Brinkkötter, Paul-Thomas (Author) , Zentgraf, Hanswalter (Author) , Navis, Gerjan (Author) , Henning, Robert H. (Author) , Van Den Born, Jacob (Author) , Bakker, Stephan J.L. (Author) , Janssen, Bart (Author) , Woude, Fokko J. van der (Author) , Yard, Benito A. (Author)
Format: Article (Journal)
Language:English
Published: August 2010
In: Diabetes
Year: 2010, Volume: 59, Issue: 8, Pages: 1984-1990
ISSN:1939-327X
DOI:10.2337/db09-0868
Online Access:Verlag, lizenzpflichtig, Volltext: https://doi.org/10.2337/db09-0868
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Author Notes:Eva Riedl, Hannes Koeppel, Frederick Pfister, Verena Peters, Sibylle Sauerhoefer, Paula Sternik, Paul Brinkkoetter, Hanswalter Zentgraf, Gerjan Navis, Robert H. Henning, Jacob Van Den Born, Stephan J.L. Bakker, Bart Janssen, Fokko J. van der Woude, and Benito A. Yard
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Summary:The (CTG)n polymorphism in the serum carnosinase (CN-1) gene affects CN-1 secretion. Since CN-1 is heavily glycosylated and glycosylation might influence protein secretion as well, we tested the role of N-glycosylation for CN-1 secretion and enzyme activity. We also tested whether CN-1 secretion is changed under hyperglycemic conditions.N-glycosylation of CN-1 was either inhibited by tunicamycin in pCSII-CN-1-transfected Cos-7 cells or by stepwise deletion of its three putative N-glycosylation sites. CN-1 protein expression, N-glycosylation, and enzyme activity were assessed in cell extracts and supernatants. The influence of hyperglycemia on CN-1 enzyme activity in human serum was tested in homozygous (CTG)5 diabetic patients and healthy control subjects.Tunicamycin completely inhibited CN-1 secretion. Deletion of all N-glycosylation sites was required to reduce CN-1 secretion efficiency. Enzyme activity was already diminished when two sites were deleted. In pCSII-CN-1-transfected Cos-7 cells cultured in medium containing 25 mmol/l d-glucose, the immature 61 kilodaltons (kDa) CN-1 immune reactive band was not detected. This was paralleled by an increased GlcNAc expression in cell lysates and CN-1 expression in the supernatants. Homozygous (CTG)5 diabetic patients had significantly higher serum CN-1 activity compared with genotype-matched, healthy control subjects.We conclude that apart from the (CTG)n polymorphism in the signal peptide of CN-1, N-glycosylation is essential for appropriate secretion and enzyme activity. Since hyperglycemia enhances CN-1 secretion and enzyme activity, our data suggest that poor blood glucose control in diabetic patients might result in an increased CN-1 secretion even in the presence of the (CTG)5 allele.
Item Description:Gesehen am 15.05.2023
Physical Description:Online Resource
ISSN:1939-327X
DOI:10.2337/db09-0868

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