Effect of metal ions on structure and activity of papain from Carica papaya

Abstract

Papain, a powerful proteolytic enzyme, is an endoprotease belonging to cysteine endopeptidase family. It is used extensively in food processing especially in tenderization of meat. In this study, we have made an attempt to show the structure activity relationship of this enzyme and the role of calcium and magnesium ions in the activity and stability of the enzyme. Results of activation and stabilization of the enzyme by these cations showed concentration dependent effect. The enzymatic activity of papain increases to a maximum of 18% and 24% in presence of calcium and magnesium ions at 1 x 10(-3) M concentration, respectively. Thermal denaturation studies showed that the binding of calcium and magnesium ions bring about change in the thermal stability of papain at various concentrations of these metal ions. Far ultraviolet circular dichroic studies showed no significant change in the alpha-helix and beta-sheet structure of the papain upon binding of these metal ions. The mechanism underlying the structure activity relationship of papain in presence of these metal ions have been discussed here with reference to the ionic radii, ligand binding preference, coordination numbers and the electrostatic forces between the protein molecule and cations present in the microenvironment of the enzyme.

Kinetics studies with fruit bromelain (Ananas comosus) in the presence of cysteine and divalent ions

“…The effects of different concentrations of Ca 2+ on fruit bromelain activity implied that the trend of the response to increasing ion concentration was consistent. These results corroborate the earlier observations ( (Kaul et al 2002;Wang et al 2009), which implied that calcium ions promote the bromelain activity by stabilizing the secondary structure of enzyme. The hydrolysis of gelatin was enhanced by 37.52 % at 0.3 mM-0.5 mM Ca 2+ ions (Fig.…”

Colorimetric detection of mercury, lead and copper ions simultaneously using protein-functionalized gold nanoparticles

“…It is a single polypeptide chain containing 212 residues, having seven cysteine residues, which may selectively interact with mercury ions (Kaul et al, 2002). Therefore, we supposed that if we functionalized AuNPs with papain, we could detect Hg 2+ using P-AuNPs just by our naked eyes.…”

Metal-Mediated Modulation of Streptococcal Cysteine Protease Activity and Its Biological Implications

“…These studies revealed that the proteolytic activity of caspase 6 can indeed be inhibited by direct binding of zinc to an exosite distal to the active site (48), whereas caspase 9, which harbors two zinc binding sites, namely, an active site and an exosite, was shown to be inhibited to a greater extent following the biding of zinc to the active site that harbors the catalytic dyad 287 Cys and 237 His (44). Similar studies done on papain, a cysteine protease derived from the papaya plant, reported that calcium and/or magnesium enhances the proteolytic activity of papain (45), whereas zinc and/or cadmium was shown to inhibit its activity (47). We can conclude that metal (especially zinc)-mediated inhibition of proteolytic activity of cysteine proteases has been a topic of thorough investigation; however, to our knowledge, metal-mediated inhibition of pathogenic bacterial proteases, and GAS in particular, is a novel mode of inhibition that we report here for the first time.…”

“…Nonetheless, several other laboratories reported the regulation of other cysteine proteases by metal ions, including zinc (44)(45)(46)(47)(48). For example, human apoptotic caspases, a family of cysteine proteases involved in apoptosis, are a recognized model for studying zinc-mediated inhibition of proteolytic activity (44,46,48).…”