Wheat endoxylanase inhibitor TAXI-I inhibits microbial glycoside hydro-lase family 11 endoxylanases. Crystallographic data of an Aspergillus niger endoxylanase-TAXI-I complex showed His374 of TAXI-I to be a key resi-due in endoxylanase inhibition [Sansen S, De Ranter CJ, Gebruers K, Brijs K, Courtin CM, Delcour JA & Rabijns A (2004)J Biol Chem279, 36022– 36028]. Its role in enzyme–inhibitor interaction was further investigated by site-directed mutagenesis of His374 into alanine, glutamine or lysine
