Characterization of Siam tulip (curcuma alismatifolia) cystatin (CaCPI)

Abstract

Cystatin is a cysteine protease inhibitor that can regulate the proteolytic process of cysteine proteases by binding to the active site of those target enzymes. Plant cystatin has several reported roles, including in: protein turnover during development; programmed cell death; and plant defense mechanisms against insects, nematodes and phytopathogenic fungi. In this experiment, the CaCPI gene was isolated from the cDNA library of the Siam tulip (Curcuma alismatifolia cv. Chiang Mai Pink). Its full length cDNA sequence is 601 base pair, containing 372 base pair in an open reading frame encoding 123 amino acids and 32 and 197 base pair in the 5'and 3' untranslated regions, respectively. The deduced amino acid sequence consists of a putative N-terminal secretory signal peptide of 22 amino acids and an estimated molecular mass for the mature protein of 11.239 kDa. The CaCPI protein contains all of the highly conserved blocks, including Gly31-Gly32, the reactive site motif QXVXG (Q76V77V78A79G80), P106-W107, and the LGRFAVDQHN block that are common among plant cystatins. The CaCPI gene was cloned into a pDEST17 expression vector and then transformed into the Escherichia coli strain BL21-Star for recombinant CaCPI protein production. After induction with 1 mM IPTG, the cell lysate of E. coli carrying pDEST17-CaCPI generated a CaCPI protein about 12 Kda in size on SDS-PAGE. This cell lysate inhibited papain activity.