Stephan Schilling, 1. probiodrug AG, Weinbergweg 22, D-06120 Halle/Saale, Germany
1 Irene Stenzel, 2. Leibniz Institute for Plant Biochemistry, P.O. Box 110432, D-06120 Halle/Saale, Germany and Present address: Department of Plant Biochemistry, Albrecht von Haller Institute of Plant Sciences; Georg August University of Göttingen, Justus-Liebig-Weg 11, D-37077 Göttingen, Germany
2 Alex von Bohlen, 3. Institute for Analytical Sciences, Bunsen-Kirchhoff-Straße 11, D-44139 Dortmund, Germany
3 Michael Wermann, 4. probiodrug AG, Weinbergweg 22, D-06120 Halle/Saale, Germany
4 Katrin Schulz, 5. probiodrug AG, Weinbergweg 22, D-06120 Halle/Saale, Germany
5 Hans-Ulrich Demuth, 6. probiodrug AG, Weinbergweg 22, D-06120 Halle/Saale, Germany
6 Claus Wasternack7. Leibniz Institute for Plant Biochemistry, P.O. Box 110432, D-06120 Halle/Saale, Germany
7 Corresponding author
Citation Information. Biological Chemistry. Volume 388, Issue 2, Pages 145–153, ISSN (Online) 1437-4315, ISSN (Print) 1431-6730, DOI: 10.1515/BC.2007.016, 01/02/2007
Publication History: Received: //; accepted: //; published online: 29/01/2007
Abstract
Glutaminyl cyclases (QCs) catalyze the formation of pyroglutamic acid at the N-terminus of several peptides and proteins. On the basis of the amino acid sequence of Carica papaya QC, we identified cDNAs of the putative counterparts from Solanum tuberosum and Arabidopsis thaliana. Upon expression of the corresponding cDNAs from both plants via the secretory pathway of Pichia pastoris, two active QC proteins were isolated. The specificity of the purified proteins was assessed using various substrates with different amino acid composition and length. Highest specificities were observed with substrates possessing large hydrophobic residues adjacent to the N-terminal glutamine and for fluorogenic dipeptide surrogates. However, compared to Carica papaya QC, the specificity constants were approximately one order of magnitude lower for most of the QC substrates analyzed. The QCs also catalyzed the conversion of N-terminal glutamic acid to pyroglutamic acid, but with approximately 105- to 106-fold lower specificity. The ubiquitous distribution of plant QCs prompted a search for potential substrates in plants. Based on database entries, numerous proteins, e.g., pathogenesis-related proteins, were found that carry a pyroglutamate residue at the N-terminus, suggesting QC involvement. The putative relevance of QCs and pyroglutamic acid for plant defense reactions is discussed.
Keywords glutaminyl cyclase, pathogenesis-related proteins, pyroglutamic acid
