This domain is found C-terminal in some aspartic proteinases and in xylanase inhibitors. The activity of these proteins is vital for plant-survival as xylanase produced by phytopathogens destroys plant cells. In TAXI-type inhibitors, this domain is important for the differences in xylanase specificity [1-3].

1: Molecular identification of wheat endoxylanase inhibitor TAXI-I1, member of a new class of plant proteins. Fierens K, Brijs K, Courtin CM, Gebruers K, Goesaert H, Raedschelders G, Robben J, Van Campenhout S, Volckaert G, Delcour JA; FEBS Lett. 2003;540:259-263. PMID:12681519

2: Structural basis for inhibition of Aspergillus niger xylanase by triticum aestivum xylanase inhibitor-I. Sansen S, De Ranter CJ, Gebruers K, Brijs K, Courtin CM, Delcour JA, Rabijns A; J Biol Chem. 2004;279:36022-36028. PMID:15166216

3: Identification of structural determinants for inhibition strength and specificity of wheat xylanase inhibitors TAXI-IA and TAXI-IIA. Pollet A, Sansen S, Raedschelders G, Gebruers K, Rabijns A, Delcour JA, Courtin CM; FEBS J. 2009;276:3916-3927. PMID:19769747