Isolation and characterization of the glutaminyl cyclases from Solanum tuberosum and Arabidopsis thaliana: implications for physiological functions.
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 10(5)- to 10(6)-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.
Schilling
Stephan
S
Probiodrug AG, Weinbergweg 22, D-06120 Halle/Saale, Germany. stephan.schilling@probiodrug.de
Stenzel
Irene
I
von Bohlen
Alex
A
Wermann
Michael
M
Schulz
Katrin
K
Demuth
Hans-Ulrich
HU
Wasternack
Claus
C
D000595:Amino Acid Sequence; D019881:Aminoacyltransferases / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology; D017360:Arabidopsis / Q000201:enzymology*; D029441:Carica / Q000201:enzymology; D002384:Catalysis; D002942:Circular Dichroism; D018076:DNA, Complementary / Q000235:genetics; D004789:Enzyme Activation / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D018698:Glutamic Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology; D011761:Pyrrolidonecarboxylic Acid / Q000138:chemical synthesis / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D012680:Sensitivity and Specificity; D016415:Sequence Alignment; D011198:Solanum tuberosum / Q000201:enzymology*; D017550:Spectroscopy, Fourier Transform Infrared
D018076:DNA, Complementary; D010940:Plant Proteins; D011994:Recombinant Proteins; D018698:Glutamic Acid; D019881:Aminoacyltransferases; C059280:glutaminyl-peptide cyclotransferase; D011761:Pyrrolidonecarboxylic Acid