Proteinases are proteolytic enzymes that catalyze the hydrolysis of peptide bonds present in proteins. These enzymes are essential for nonspecific digestion of intracellular and extracellular proteins and are specifically required for proteolytic cleavage of inactive precursors, activation of zymogens, processing of hormones and neuropeptides, activation of receptors, protein translocation through membranes etc
. (Neurath, 1984
). If the proteolytic activity of these enzymes is not restrained then it can be hazardous for the cells and tissues. Therefore, the activity of proteases is tightly controlled by various regulatory mechanisms such as the regulation of enzyme expression or secretion, the specific degradation of the active form of the enzyme and the inhibition of proteolytic activity by the formation of enzyme complexes with proteinase inhibitors (PIs). Many cells, tissues and organisms produce PIs that are proteins for regulating the enzymatic activity of endogenous proteases (Laskowski & Kato, 1980
; Bode & Huber, 2000
; Krowarsch et al.
In plants, PIs consist of a large and assorted group of proteins that have the ability to inhibit proteases by making a reversible inhibitory complex with the enzyme (Laskowski & Kato, 1980
; Richardson, 1977
). Plant proteinase inhibitors (PPIs) play a major role in the defensive mechanism against phytophagous insect infestation and microorganisms. The defensive capability of PPIs is dependent on their ability to inhibit peptidases which are secreted in the gut of insects or by infectious microbes. PPIs isolated from legume seeds have mainly been grouped into Kunitz, Bowman–Birk, potato I and II, squash, cereal superfamily and thaumatin-like proteinacous inhibitors. Proteinase inhibitors of the Kunitz-type family are proteins with a molecular weight of approximately 18–24 kDa and usually contain four Cys residues forming two intramolecular disulfide bridges (Richardson, 1991
; Pandya et al.
). The tamarind tree (Tamarindus indica
), a member of the Leguminosae family, grows naturally in many tropical and subtropical regions of the world. Tamarind-fruit pulp is an important food ingredient and tamarind-kernel powder (TKP) is used as a stabilizer and an emulsifier in the food industry (Kumar & Bhattacharya, 2008
In this study, we have successfully purified and crystallized a Kunitz-type proteinase inhibitor from the seeds of T. indica
. The molecular weight of the purified proteinase inhibitor is about 21 kDa (Araújo et al.
; Rao & Gowda, 2008
). The purified protein is active towards trypsin. Here, we report the isolation, purification, crystallization and preliminary X-ray diffraction analysis of the Kunitz-type proteinase inhibitor from T. indica