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Publication : Isolation of an isoenzyme of human glutaminyl cyclase: retention in the Golgi complex suggests involvement in the protein maturation machinery.

First Author  Cynis H Year  2008
Journal  J Mol Biol Volume  379
Issue  5 Pages  966-80
PubMed ID  18486145 Mgi Jnum  J:168887
Mgi Id  MGI:4939132 Doi  10.1016/j.jmb.2008.03.078
Citation  Cynis H, et al. (2008) Isolation of an isoenzyme of human glutaminyl cyclase: retention in the Golgi complex suggests involvement in the protein maturation machinery. J Mol Biol 379(5):966-80
abstractText  Mammalian glutaminyl cyclase isoenzymes (isoQCs) were identified. The analysis of the primary structure of human isoQC (h-isoQC) revealed conservation of the zinc-binding motif of the human QC (hQC). In contrast to hQC, h-isoQC carries an N-terminal signal anchor. The cDNAs of human and murine isoQCs were isolated and h-isoQC, lacking the N-terminal signal anchor and the short cytosolic tail, was expressed as a fusion protein in Escherichia coli. h-isoQC exhibits 10fold lower activity compared to hQC. Similar to hQC, h-isoQC was competitively inhibited by imidazoles and cysteamines. Inactivation by metal chelators suggests a conserved metal-dependent catalytic mechanism of both isoenzymes. A comparison of the expression pattern of m-isoQC and murine QC revealed ubiquitous expression of both enzymes. However, murine QC transcript formation was higher in neuronal tissue, whereas the amount of m-isoQC transcripts did not vary significantly between different organs. h-isoQC was exclusively localized within the Golgi complex, obviously retained by the N-terminus. Similar resident enzymes of the Golgi complex are the glycosyltransferases. Golgi apparatus retention implies a 'housekeeping' protein maturation machinery conducting glycosylation and pyroglutamyl formation. For these enzymes, apparently similar strategies evolved to retain the proteins in the Golgi complex.
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