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Glutaminyl cyclases (QCs) catalyze the formation of pyroglutamate resi-dues at the N-terminus of several peptides and proteins from plants and animals. Recently, isoenzymes of mammalian QCs have been identified. In order to gain further insight into the biochemical characteristics of iso-QCs, the human and murine enzymes were expressed in the secretory pathway ofPichia pastoris. | Mammalian glutaminyl cyclases and their isoenzymes have identical enzymatic characteristics Anett Stephan1 Michael Wermann1 Alex von Bohlen2 Birgit Koch1 Holger Cynis1 Hans-Ulrich Demuth1 and Stephan Schilling1 1 Probiodrug AG Halle Saale Germany 2 Institute for AnalyticalSciences Dortmund Germany Keywords Alzheimer s disease glutaminylcyclase isoenzyme glycosylation Golgi apparatus Pichia pastoris Correspondence S. Schilling Probiodrug AG Weinbergweg 22 06120 Halle Saale Germany Fax 49 345 5559901 Tel 49 345 5559911 E-mail stephan.schilling@probiodrug.de Received 30 June 2009 revised 17 August 2009 accepted 28 August 2009 doi 10.1111 j.1742-4658.2009.07337.x Glutaminyl cyclases QCs catalyze the formation of pyroglutamate residues at the N-terminus of several peptides and proteins from plants and animals. Recently isoenzymes of mammalian QCs have been identified. In order to gain further insight into the biochemical characteristics of iso-QCs the human and murine enzymes were expressed in the secretory pathway of Pichia pastoris. Replacement of the N-terminal signal anchor by an a-factor prepropeptide from Saccharomyces cerevisiae resulted in poor secretion of the protein. Insertion of an N-terminal glycosylation site and shortening of the N-terminus improved isoQC secretion 100-fold. A comparison of different recombinant isoQC proteins did not reveal an influence of mutagenic changes on catalytic activity. An initial characterization showed identical modes of substrate conversion of human isoQC and murine isoQC. Both proteins displayed a broad substrate specificity and preference for hydrophobic substrates similar to the related QC. Likewise a determination of the zinc content and reactivation of the apo-isoQC revealed equimolar zinc present in QC and isoQC. Far-UV CD spectroscopic analysis of murine QC and isoQC indicated virtually identical structural components. The present investigation provides the first enzymatic characterization of mammalian isoQCs. QC and
