Characterization of five new low-molecular-mass trypsin inhibitors from white mustard (Sinapis alba L.) seed.
Five new low-molecular-mass trypsin inhibitors belonging to the RTI/MTI-2 family were identified from white mustard (Sinapis alba L. ; MTI-2) seed. Purified MTI-2 consisted of a peptide mixture, displaying Ile or Arg at position 43, Trp or kynurenine (Kyn) at position 44, and C-terminal ragged ends. The occurrence of Ile or Arg at position 43 suggested that MTI-2 inhibitors originated from different genes. The presence of 5-oxo-proline (pyroglutamic acid; 5-oxoPro1) and Kyn44 reflected post-translational processing of the serine proteinase inhibitor. MTI-2 showed approximately 70% amino-acid identity with low-molecular-mass trypsin inhibitors isolated from oil rape (Brassica napus var. oleifera; RTI-III) seed and with serine proteinase inhibitors mapped in Arabidopsis thaliana chromosome II (ATTI). Furthermore, MTI-2 was homologous to brazzein, the sweet-tasting protein from Pentadiplandra brazzeana Baillon fruit ( approximately 30% amino-acid identity). Although snake-venom toxins showed a low amino-acid identity (< 20%) with MTI-2, RTI-III, and ATTI, some structurally relevant residues were conserved. The disulfide bridge pattern of MTI-2 (Cys5-Cys27, Cys18-Cys31, Cys42-Cys52, and Cys54-Cys57) corresponded to that of RTI-III and of snake-venom toxins, being different from that of brazzein. Therefore, protein similarity might be attributable to the three-dimensional arrangement rather than to the amino-acid sequence. Values of Ka for MTI-2 binding to bovine beta-trypsin (trypsin) and bovine alpha-chymotrypsin were 6.3 x 109 M-1 and 2.0 x 106 M-1, respectively, at pH 8.0 and 21.0 degrees C. Moreover, values of kon for MTI-2 binding to trypsin and of koff for the dissociation of the serine proteinase:inhibitor complex were 5.6 x 105 M-1.s-1 and 8.9 x 10-5 M-1.s-1, respectively, at pH 8.0 and 21.0 degrees C. Despite the heterogeneity of the purified inhibitor peptide mixture, the inhibition properties of the different MTI-2 inhibitors were indistinguishable.
Ruoppolo
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M
Dipartimento di Chimica, Università di Salerno, Italy.
Amoresano
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A
Pucci
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Pascarella
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Polticelli
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Trovato
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Menegatti
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Ascenzi
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D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D002918:Chymotrypsin / Q000037:antagonists & inhibitors / Q000378:metabolism; D004220:Disulfides / Q000032:analysis; D010450:Endopeptidases / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009149:Mustard Plant / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D010946:Plants, Medicinal; D012639:Seeds / Q000737:chemistry*; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013816:Thermodynamics; D013820:Thermolysin / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism; D014361:Trypsin Inhibitors / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*
D004220:Disulfides; C405940:MTI2 protein, Sinapis alba; D010446:Peptide Fragments; D010940:Plant Proteins; D014361:Trypsin Inhibitors; D010450:Endopeptidases; D002918:Chymotrypsin; D014357:Trypsin; D013820:Thermolysin; C044574:lysine-C peptidase