Triticum aestivum L. endoxylanase inhibitor (TAXI) consists of two inhibitors, TAXI I and TAXI II, with different specificities

Abstract

The Triticum aestivum L. endoxylanase inhibitor (TAXI) discovered by Debyser and Delcour [(1997) Eur. Pat. filed April 1997, published as WO 98/49278] and Debyser, Derdelinckx and Delcour [(1997) J. Am. Soc. Brew. Chem. 55, 153-156] seems to be a mixture of two different endoxylanase inhibitors, called TAXI I and TAXI II. By using Aspergillus niger as well as Bacillus subtilis endoxylanases for assaying inhibition activity, both inhibitors could be purified to homogeneity from wheat (Triticum aestivum L., var. Soissons). TAXI I and TAXI II have similar molecular structures. They both have a molecular mass of approx. 40.0 kDa, are not glycosylated and occur in two molecular forms, i.e. a non-proteolytically processed one and a proteolytically processed one. However, the pI of TAXI II (at least 9.3) is higher than that of TAXI I (8.8). TAXI I and TAXI II clearly show different inhibition activities towards different endoxylanases. The N-terminal amino acid sequences of both inhibitors show a high degree of identity, which might indicate that there is an evolutionary relationship between them.

Molecular identification of wheat endoxylanase inhibitor TAXI‐I1, member of a new class of plant proteins

“…The inhibition activities against xylanases from Aspergillus niger (SWISS-PROT P55329, xylanase M4, Megazyme, Bray, Ireland) and B. subtilis (Puratos, Groot-Bijgaarden, Belgium) were determined with a variant of the colorimetric Xylazyme-AX method of Megazyme as described by Gebruers et al [13]. One enzyme unit corresponds to an increase in absorbance at 590 nm of 1.0 under the conditions of the assay.…”

“…One inhibition unit (IU) is the amount of inhibitor that, under the conditions of the assay, reduces the A 590 nm of one enzyme unit by 50% (to 0.5). SDS^PAGE and isoelectric focusing analysis of the recombinant inhibitor were performed as described earlier [13].…”

“…Enzymatic digestion, peptide puri¢cation and Edman degradation of puri¢ed natural TAXI-I protein yielded, besides the previously identi¢ed N-terminal amino acid sequences [13], novel amino acid sequences of three internal peptides. All sequences were used to screen Triticeae expressed sequence tag (EST) sequence databases with tBLASTn [24] yielding ¢ve matching wheat nucleotide sequences (Table 1).…”

“…Our group previously discovered and partially characterized proteinaceous xylanase inhibitors in wheat (Triticum aestivum) [10,11] and denominated them TAXIs (for T. aestivum endoxylanase inhibitors) [12]. Wheat contains TAXI-I and TAXI-II protein types [13], which di¡er in enzyme inhibition speci-¢city. Both types have similar structures and N-terminal amino acid sequences and occur in two forms, A and B.…”

Characterization of a newly identified rice chitinase-like protein (OsCLP) homologous to xylanase inhibitor

“…These proteins are thought as “defense molecules” that protect plant cells from attack by pathogenic hydrolytic enzymes [11]. Two types of plant xylanase inhibitors have been well studied, i.e., xylanase-inhibiting protein (XIP)-type inhibitors [12] and Triticum aestivum xylanase inhibitor (TAXI)-type inhibitors [13,14]. Biochemical analysis revealed that a wheat XIP specifically inhibits the expression of family-10 and −11 xylanases from Aspergillus nidulans and Aspergillus niger , respectively [15], while a TAXI inhibits the expression of the family-11 xylanase (but not the family-10 xylanase) of A. niger and Bacillus subtilis [13,16].…”