Chelidocystatin, a novel phytocystatin from Chelidonium majus

Greater celandine (Chelidonium majus L.) has traditional uses in European and Chinese herbal medicine. In the plant sap significant inhibitory activity against papain was observed. A cysteine proteinase inhibitor, named chelidocystatin, was isolated from the plant using papain Sepharose affinity chromatography followed by gel filtration and ion-exchange chromatography. Chelidocystatin showed a M(r) of 10,000 on SDS-PAGE with the pI of 9.3, and was a strong inhibitor of cathepsin L (Ki = 5.6 x 10(-11) M), papain (Ki = 1.1 x 10(-10) M) and cathepsin H (Ki = 7.5 x 10(-9) M). The complete amino acid sequence of the protein was obtained with N-terminal sequencing and sequencing of the peptides after digestion of the protein. Moreover, a major part of the sequence was verified by molecular cloning. The conserved glycine residue at the N-terminal region and the QVVAG motif, which are both believed to be involved in the inhibitory activity, indicate that it is a member of the cystatin superfamily. The amino acid sequence of chelidocystatin shows a high degree of homology with cysteine proteinase inhibitors belonging to the phytocystatin group, especially with the recently described carrot and sunflower phytocystatins with which it shares 57% and 54% homology, respectively.