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Characterization of inhibitory mechanism and antifungal activity between group‐1 and group‐2 phytocystatins from taro ( Colocasia esculenta )
Author(s) -
Wang KeMing,
Kumar Senthil,
Cheng YiSheng,
Venkatagiri Shripathi,
Yang AiHwa,
Yeh KaiWun
Publication year - 2008
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2008.06631.x
Subject(s) - peptide , papain , cystatin , non competitive inhibition , biochemistry , cysteine proteinase inhibitors , colocasia esculenta , biology , chemistry , enzyme , cystatin c , botany , apoptosis , programmed cell death , renal function , caspase
Tarocystatin from Colocasia esculenta , a group‐2 phytocystatin, is a defense protein against phytopathogenic nematodes and fungi. It is composed of a highly conserved N‐terminal region, which is homological to group‐1 cystatin, and a repetitive peptide at the C‐terminus. The purified recombinant proteins of tarocystatin, such as full‐length (FL), N‐terminus (Nt) and C‐terminus (Ct) peptides, were produced and their inhibitory activities against papain as well as their antifungal effects were investigated. Kinetic analysis revealed that FL peptide exhibited mixed type inhibition ( K ia = 0.098 μ m and K ib = 0.252 μ m ) and Nt peptide showed competitive inhibition ( K i = 0.057 μ m ), whereas Ct peptide possessed weak papain activation properties. A shift in the inhibitory pattern from competitive inhibition of Nt peptide alone to mixed type inhibition of FL peptide implied that the Ct peptide has an regulatory effect on the function of FL peptide. Based on the inhibitory kinetics of FL (group‐2) and Nt (group‐1) peptides on papain activity, an inhibitory mechanism of group‐2 phytocystatins and a regulatory mechanism of extended Ct peptide have each been proposed. By contrast, the antifungal activity of Nt peptide appeared to be greater than that of FL peptide, and the Ct peptide showed no effect on antifungal activity, indicating that the antifungal effect is not related to proteinase inhibitory activity. The results are valid for most phytocystatins with respect to the inhibitory mechanism against cysteine proteinase.