Highly stable glycosylated serine protease from the medicinal plant Euphorbia milii

• Published in: Phytochemistry (Oxford) 2006-07, Vol.67 (14), p.1414-1426
• Main Authors: Yadav, Subhash C., Pande, Monu, Jagannadham, M.V.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; amino acid sequences; Amino Acids - chemistry; Anti-milin; Biological and medical sciences; carbohydrates; casein; Catalysis; Chromatography, Liquid; enzyme activity; enzyme inhibition; Enzyme Stability; enzyme substrates; Enzymes; Euphorbia; Euphorbia - enzymology; Euphorbia milii; Euphorbiaceae; Fundamental and applied biological sciences. Psychology; glycoproteins; Glycosylation; Hydrogen-Ion Concentration; Isoelectric Focusing; medicinal plants; Metabolism; Milin; Molecular Sequence Data; Molecular Weight; plant biochemistry; Plant endopeptidases; Plant physiology and development; Plants, Medicinal - enzymology; proteolysis; sequence analysis; Serine Endopeptidases - chemistry; Serine Endopeptidases - isolation & purification; Serine Endopeptidases - metabolism; Serine proteases; serine proteinases; Substrate Specificity; Temperature
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2006.06.002

A glycosylated serine protease from the latex of medicinal plant Euphorbia milii has been isolated, and comprehensively studied. Its activity over a broad range of pH and temperature, high stability against the chemical and physiological denaturants and less susceptibility to autodigestion makes the enzyme applicable in biotechnology industries. A serine protease, named as “Milin” was purified to homogeneity from the latex of Euphorbia milii, a medicinal plant of Euphorbiaceae family. The molecular mass (SDS–PAGE), optimum pH and temperature of the enzyme were 51 kDa, pH 8.0 and 60 °C, respectively. Milin retains full proteolytic activity over a wide range of pH (5.5–12) and temperature (up to 65 °C) with casein and azoalbumin as substrates. The activity of milin is inhibited by serine proteases inhibitors like PMSF, APMSF and DFP, but not by any other protease inhibitors such as E-64 and PCMB. Like the other serine proteases from the genus Euphorbia, the activity of milin was not inhibited by the proteinaceous inhibitor soyabean trypsin inhibitor (SBTI) even at very high concentrations that is naturally present in plants. The specific extinction coefficient ( ε 280 nm 1 % ), molar extinction coefficient ( a m) and isoelectric point of the enzyme were found to be 29, 152,500 M −1 cm −1 and pH 7.2, respectively. The enzyme is a glycoprotein with detectable carbohydrate moiety (7–8%) in its constitution, which is essential for the activity. The numbers of tryptophan, tyrosine and cysteine residues in the sequence of milin were estimated chemically and are 23, 14 and 14, respectively. Of the 14-cysteine residues, 12 constituted 6-disulfide linkages while two are free cysteines. The N-terminal sequence (first 12 amino acid residues) was determined and does not match with any sequence of known plant serine proteases. Perturbation studies by temperature, pH and chaotropes of the enzyme also reveal its high stability as seen by CD, fluorescence and proteolytic activity. Thus, this serine protease may have potential applications in food industry.