Glutaminyl cyclases unfold glutamyl cyclase activity under mild acid conditions

Abstract

N-terminal pyroglutamate (pGlu) formation from glutaminyl precursors is a posttranslational event in the processing of bioactive neuropeptides such as thyrotropin-releasing hormone and neurotensin during their maturation in the secretory pathway. The reaction is facilitated by glutaminyl cyclase (QC), an enzyme highly abundant in mammalian brain. Here, we describe for the ¢rst time that human and papaya QC also catalyze N-terminal glutamate cyclization. Surprisingly, the enzymatic Glu 1 conversion is favored at pH 6.0 while Gln 1 conversion occurs with an optimum at pH 8.0. This unexpected ¢nding might be of importance for deciphering the events leading to deposition of highly toxic pyroglutamyl peptides in amyloidotic diseases. ß 2004 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.

Oleuropein aglycone protects against pyroglutamylated-3 amyloid-ß toxicity: biochemical, epigenetic and functional correlates

“…It is known that pE3-Aß is generated both in vitro and in vivo via QC-catalyzed cyclization of the N-terminal glutamate residues present in the truncated Aß species Schilling et al, 2004) and that both pE3-Aß levels and QC activity are increased in the AD brain . Therefore, we firstly checked whether OLE was able to inhibit directly QC activity in vitro by using recombinant QC and Q-AMC as a substrate.…”

“…The modification which originates the pE-Aß peptides is catalyzed by glutaminyl cyclase (QC, also known as QPCT) both in vitro (Schilling et al, 2004) and in vivo (Cynis et al, 2006Nussbaum et al, 2012;Schilling et al, 2008). In the mammalian brain, a physiologically relevant neuronal expression of QC was described in the hypothalamus, and enzyme involvement in neuropeptide and hormone maturation was shown (Bockers et al, 1995;Fischer and Spiess, 1987).…”

Identification of plasma protease derived metabolites of glucagon and their formation under typical laboratory sample handling conditions

“…[28] It is possible that such enzymes are less active in plasma than in buffered serum, thereby allowing significant levels of glucagon to remain. The enzymatic nature of the cyclisation may also explain why it does not occur for position 2 modified glucagon analogs [13] , as these may introduce steric hindrance.…”

“…Peaks 3, 4, and 5 were confirmed as glucagon [21][22][23][24][25][26][27][28][29], glucagon 20-29, and glucagon [19][20][21][22][23][24][25][26][27][28][29] to within 3.8 ppm. These peaks showed lower mass accuracies than the other metabolites, which is likely to be due to their lower abundances limiting mass spectrometer signal.…”

“…Glucagon [1][2][3][4][5][6][7][8][9][10][11][12][13] and glucagon [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] , and the minor metabolites glucagon [1][2][3][4][5][6][7][8][9][10] , glucagon [14][15][16][17][18][19][20][21][22][23][24][25] and glucagon [23][24]…”