Sorghum (Sorghum bicolor L. Moench) contains a XIP-type xylanase inhibitor but none of the TAXI- and TLXI-types

A xylanase inhibitor of the xylanase-inhibiting protein (XIP) type was detected in sorghum (Sorghum bicolor L. Moench) whole meal using Western blot and immunoprobing with polyclonal anti-XIP antibodies. No detectable levels of Triticum aestivum xylanase inhibitor (TAXI) and thaumatin-like xylanase inhibitor (TLXI) type xylanase inhibitors were present. Trichoderma longibrachiatum xylanase affinity chromatography (AC) was used for the purification of sorghum XIP. Biochemical characteristics and protein sequence data show that sorghum XIP strongly corresponds to wheat (T. aestivum L.) XIP-I. Like wheat XIP-I, it inhibits both glycoside hydrolase family (GH) 10 and 11 xylanases, indicating that the XIP-I active site residues are well conserved in sorghum XIP. However, in contrast to wheat XIP-I, the inhibitor is unable to affect Aspergillus niger GH 11 xylanase activity. Its specific inhibition activities towards the other xylanases tested are comparable to those of wheat XIP-I. Based on the available sorghum expressed sequence tag (EST) database, XIP is expressed in sorghum in different tissues and developmental stages. Also expression in the presence of several plant hormones and under biotic as well as abiotic stress conditions is suggested.