Glutaminyl cyclase

Several proteins and bioactive peptides contain an N-terminal pyroglutamic acid residue produced by cyclization of an N-terminal glutaminyl residue. This assay for glutaminyl cyclase follows the reaction for a model peptide. 

The substrate, Gln-Leu-Tyr-Glu-Asn-Lys-t-(dansyl)-OH, is separated from the product containing the N-terminal pyroglutamyl residue by chromatography on a Hypersil ODS column (4.6 mm x 100 mm). The mobile phase contained 100 mM sodium acetate (pH 6.5) in 24% acetonitrile. A fluorescence detector was used with excitation at 352 to 360 nm and emission at 482 nm. Fluorescence detection is about 100 times more sensitive than monitoring absorbance at 340 nm. 

The enzymatic reaction was carried out in 50 mM Tris-HQ (pH 8.0) and was initiated by adding either the protein extract (up to 0.5 mg/mL) or peptide substrate (1-98 nM). Aliquots of 10 to 20 nL were removed at various times, and the reaction was quenched by the addition of 10 fiL of 10 mM phenanthroline. Aliquots of 10 nL were then analyzed by HPLC. 

The source of glutaminyl cyclase was bovine pituitaries. Extracts were partially purified by ammonium sulfate fractionation and chromatography on Sephacryl S-300. 

---

Schilling, S., Hoffmann, T., Rosche, F., Manhart, S., Wasternack, C. and Demuth, H. U. Heterologous expression and characterization of human glutaminyl cyclase evidence for a disulfide bond with importance for catalytic activity. Biochemistry 41 10849-10857,2002. 

Benzimidazole-based glutaminyl cyclase inhibitors Benzimidazolyl-1,2,3 -triazoles Benzimidazolyl-1,3,4 -thiadiazoles... 

Glutaminyl cyclase (hQC) represents a new potential target for the treatment of AD, since inhibition of hQC prevents the formation of the Ap3(pE)-40,42-species. Novel molecules containing benzimidazole as the metal binding group connected to 1,3,4-oxadiazole as the central scaffold were identified. Benzimidazolyl-1,3,4-thiadiazoles and -1,2,3-triazoles display inhibitory potency in the nano-molar range [557]. 

Glutaminyl cyclase (QC), EC 2.3.2.5, an acyltransferase responsible for N-terminal pyroglutamate formation from glutaminyl precursors in peptides and proteins. The first QC was isolated from the latex of Car-ica papaya in 1963. Later, it was established that glutaminyl cyclases occur in both animal and plant sources. They are abundant in mammalian neuroendocrine tissues, such as hypothalamus and pituitary, and are highly conserved from yeast to human. From the crystal structure of human glutaminyl cyclase it follows that a single zinc ion in the active site is coordinated... 

Initiation capability for plaque formation is managed by glutaminyl cyclase, responsible for the cyclization of N-terminus of Ap. 

Inhibition of human glutaminyl cyclase A potential new treatment for AD... 

---