Indicain, a dimeric serine protease from Morus indica cv. K2 |
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Authors: | Singh Vijay Kumar Patel Ashok Kumar Moir A J Jagannadham Medicherla V |
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Affiliation: | Molecular Biology Unit, Institute of Medical Sciences, Banaras Hindu University, Varanasi 221 005, India. |
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Abstract: | A high molecular mass serine protease has been purified to homogeneity from the latex of Morus indica cv. K2 by the combination of techniques of ammonium sulfate precipitation, hydrophobic interaction chromatography, and size-exclusion chromatography. The protein is a dimer with a molecular mass of 134.5 kDa and with two monomeric subunits of 67.2 kDa and 67.3 (MALDI-TOF), held by weak bonds susceptible to disruption on exposure to heat and very low pH. Isoelectric point of the enzyme is pH 4.8. The pH and temperature optima for caseinolytic activity were 8.5 and 80 degrees C, respectively. The extinction coefficient (epsilon280(1%)) of the enzyme was estimated as 41.24 and the molecular structure consists of 52 tryptophan, 198 tyrosine and 42 cysteine residues. The enzyme activity was inhibited by phenylmethylsulfonylflouride, chymostatin and mercuric chloride indicating the enzyme to be a serine protease. The enzyme is fairly stable and similar to subtilases in its stability toward pH, strong denaturants, temperature, and organic solvents. Polyclonal antibodies specific to enzyme and immunodiffusion studies reveal that the enzyme has unique antigenic determinants. The enzyme has activity towards broad range of substrates comparable to those of subtilisin like proteases. The N-terminal residues of indicain (T-T-N-S-W-D-F-I-G-F-P) exhibited considerable similarity to those of other known plant subtilases, especially with cucumisin, a well-characterized plant subtilase. This is the first report of purification and characterization of a subtilisin like dimeric serine protease from the latex of M. indica cv. K2. Owing to these unique properties the reported enzyme would find applications in food and pharma industry. |
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Keywords: | BAPA, NR-benzoylarginine p-nitroanilide BLAST, basic local alignment search tool BSA, bovine serum albumin DFP, diisopropylfluorophosphate DMSO, dimethyl sulfoxide DTNB, 5,5μ-dithiobis(2-nitrobenzoic acid) E-64, 3S)-3-(N-{(S)-1-[N-(4-guanidinobutyl)carbamoyl]3-ethylbutyl}carbamoyl)oxirane-2-carboxylic acid EDTA, ethylene diammine tetra acetic acid EGTA, ethylene glycol-bis(α-amino ethyl ether)tetraacetic acid GuHCl, guanidine hydrochloride GuSCN, guanidine isothiocynate IAA, iodoacetic acid MALDI-TOF, matrix assisted laser desorption/ionization time-of-flight MES, 2-(N-morpholino)ethanesulfonic acid NCBI, National Center for Biotechnology Information NEM, N-ethyl maleimide PAGE, polyacrylamide gel electrophoresis PCMB, p-chloromercuribenzoate PMSF, phenylmethanesulfonyl fluoride SBTI, soybean trypsin inhibitor SDS, sodium dodecyl sulfate |
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