Isolation of an isoenzyme of human glutaminyl cyclase: retention in the Golgi complex suggests involvement in the protein maturation machinery.
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.
Cynis
Holger
H
Probiodrug AG, Weinbergweg 22, 06120 Halle/Saale, Germany.
Rahfeld
Jens-Ulrich
JU
Stephan
Anett
A
Kehlen
Astrid
A
Koch
Birgit
B
Wermann
Michael
M
Demuth
Hans-Ulrich
HU
Schilling
Stephan
S
D000595:Amino Acid Sequence; D019881:Aminoacyltransferases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D006031:Glycosylation; D006056:Golgi Apparatus / Q000201:enzymology*; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000201:enzymology; D014018:Tissue Distribution
D018076:DNA, Complementary; D007527:Isoenzymes; D011994:Recombinant Proteins; D019881:Aminoacyltransferases; C059280:glutaminyl-peptide cyclotransferase