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

Triticum aestivum endoxylanase inhibitors (TAXIs) are wheat proteins that inhibit family 11 endoxylanases commonly used in different (bio)technological processes. Here, we report on the identification of the TAXI-I gene which encodes a mature protein of 381 amino acids with a calculated molecular mass of 38.8 kDa. When expressed in Escherichia coli, the recombinant protein had the specificity and inhibitory activity of natural TAXI-I, providing conclusive evidence that the isolated gene encodes an endoxylanase inhibitor. Bioinformatical analysis indicated that no conserved domains nor motifs common to other known proteins are present. Sequence analysis revealed similarity with a glycoprotein of carrot and with gene families in Arabidopsis thaliana and rice, all with unknown functions. Our data indicate that TAXI-I belongs to a newly identified class of plant proteins for which a molecular function as glycoside hydrolase inhibitor can now be suggested.