The Complete Amino Acid Sequence of Rice Bran Trypsin Inhibitor1

Abstract

The complete amino acid sequence of a double-headed trypsin inhibitor (RBTI) from rice bran was determined by a combination of limited proteolysis of the native inhibitor with Streptomyces griseus trypsin at pH 3 and conventional methods. RBTI consists of 133 amino acid residues including 18 half-cystine residues which are involved in 9 disulfide bridges in the molecule. The limited proteolysis at pH 3 produced a major split of Lys(83)-Met(84) and a minor split of Arg(107)-Val(108) together with a non-enzymatic hydrolysis of Asp(19)-Pro(20) in the molecule. The established sequence showed that RBTI is composed of 4 domains, domains I and III, and domains II and IV being homologous to the first and the second domains of soybean Bowman-Birk inhibitor, respectively, indicating that RBTI has a duplicated structure of the Bowman-Birk type inhibitor.

The amino acid sequence of a cereal Bowman‐Birk type trypsin inhibitor from seeds of Jobs' tears (Coix lachryma‐jobi L.)

“…The composition calculated from the sequence is also very similar to that reported for the Coix 12 kDa trypsin inhibitor by Ohtsubo et al [24] when the latter is recalculated for a protein of 7 kDa. Fig.3 shows the clear sequence homology which exists between the Coix trypsin inhibitor, rice bran inhibitor [23], wheat germ inhibitors [22] and Bowman-Birk proteinase inhibitors from a number of legumes [31][32][33][34][35][36][37]. The legume inhibitors have …”

“…Homology of the amino acid sequences of the Bowman-Birk family of proteinase inhibitors from legumes and cereals. (1) Inhibitor CII from soybean (Giycine max) [31]; (2) inhibitor AII from peanut (Arachis hypogaea) [32]; (3) adzuki bean (Phaseolus angularis) [33]; (4) Macrotyioma axiilare [34]; (5) Vicia angustifolia [35]; (6) mung bean (Phaseolus radiata) [36]; (7) alfalfa leaf (Medicago sativa) [37]; (8) rice bran (Oryza sativa) residues 1-69 [23], residues 70-133 are an internal duplication homologous with residues 3-69, and are shown as 8*; (9) wheat germ (Triticum aestivum) II-4 incomplete sequence [22]; (10) wheat I-2h incomplete sequence [22]; (11) Jobs' tears (Coix lachryma-jobO. On the numbering of the soybean (top line) and the Coix (bottom) sequences are shown.…”

“…The rice bran inhibitor on the other hand appears to ex-ist only in the inhibitor I (14.5 kDa duplicated) form [23]. Other workers have recently reported the isolation of a 12 kDa trypsin inhibitor from seeds of the cereal crop Jobs' tears (Coix lachryma-jobO [24], which they suggest might be similar to the inhibitor I forms in wheat germ and rice bran.…”

“…The sequences of probable tr-amylase/proteinase inhibitors from barley [17,18] and rice [19] suggest that they should be included with the ragi I-2 a-amylase inhibitor [20] as a separate family. The diversity of structures to be found amongst the enzyme inhibitors has been further emphasized by the recent report that a maize inhibitor of trypsin and insect a~-amylases [21] has strong homology with the sweet protein thaumatin and a pathogenesisrelated protein induced in tobacco by infection with tobacco mosaic virus, and the finding that trypsin inhibitors from wheat germ [22] and rice bran [23] have strong structural affinities with the Bowman-Birk family of proteinase inhibitors from legumes.…”

“…The larger type I inhibitor of rice bran [23] differs in the presence of an internal duplication, residues 70-133 (8* in fig.3) corresponding to residues 3-69 (8 in fig.3). The sequences reported for the type I and II inhibitors of wheat are incomplete, but an internal duplication also appears to be present in the former [22].…”