Identification of structural determinants for inhibition strength and specificity of wheat xylanase inhibitors TAXI‐IA and TAXI‐IIA

Abstract

Triticum aestivum xylanase inhibitor (TAXI)-type inhibitors are active against microbial xylanases from glycoside hydrolase family 11, but the inhibition strength and the specificity towards different xylanases differ between TAXI isoforms. Mutational and biochemical analyses of TAXI-I, TAXI-IIA and Bacillus subtilis xylanase A showed that inhibition strength and specificity depend on the identity of only a few key residues of inhibitor and xylanase [Fierens K et al. Crystallographic analysis of the structures of TAXI-IA and TAXI-IIA in complex with glycoside hydrolase family 11 B. subtilis xylanase A now provides a substantial explanation for these observations and a detailed insight into the structural determinants for inhibition strength and specificity. Structures of the xylanase-inhibitor complexes show that inhibition is established by loop interactions with active-site residues and substrate-mimicking contacts in the binding subsites. The interaction of residues Leu292 of TAXI-IA and Pro294 of TAXI-IIA with the )2 glycon subsite of the xylanase is shown to be critical for both inhibition strength and specificity. Also, detailed analysis of the interaction interfaces of the complexes illustrates that the inhibition strength of TAXI is related to the presence of an aspartate or asparagine residue adjacent to the acid ⁄ base catalyst of the xylanase, and therefore to the pH optimum of the xylanase. The lower the pH optimum of the xylanase, the stronger will be the interaction between enzyme and inhibitor, and the stronger the resulting inhibition.

Secretome analysis reveals effector candidates associated with broad host range necrotrophy in the fungal plant pathogen Sclerotinia sclerotiorum

“…It may therefore be hypothesized that a subset of S. sclerotiorum critical secreted enzymes are engaged in an evolutionary arms race with plant pattern recognition receptors, driving opposing forces of natural selection S. sclerotiorum effector genes. Since plant inhibitors are known for many fungal cell wall degrading enzymes, it is also possible that an evolutionary arms race with plant inhibitors drives the evolution of some S. sclerotiorum effector candidates [53, 62, 63]. Remarkably, we also identified 14.4% of species-specific SPEP genes.…”

Crystal structure of basic 7S globulin, a xyloglucan‐specific endo‐β‐1,4‐glucanase inhibitor protein‐like protein from soybean lacking inhibitory activity against endo‐β‐glucanase

“…In contrast, Leu292 in IL‐1 of TAXI‐IA undergoes a hydrophobic interaction with Tyr10 of ANXY. The interactions mimic those in the enzyme–substrate complexes (PDB ID 1BCX and 2QZ2) [7,9]. In addition, His374 of TAXI‐IA interacts with Asp37 of ANXY.…”

“…The structure of TAXI‐IA in complex with Aspergillus niger xylanase (ANXY), a GH11 xylanase from Aspergillus niger , coupled with functional studies, has revealed that His374 of TAXI‐IA plays a significant role in the inhibition of ANXY, where His374 interacts with the catalytic Glu79 and Glu170 of ANXY [7,8]. Furthermore, it has been reported that the hydrophobic interaction of Leu292 of TAXI‐IA with Pro294 of TAXI‐IIB regulates the strength of inhibition and specificity for GH11 xylanases [9].…”

Cloning, Expression, and Purification of Xylanase Gene from Bacillus licheniformis for Use in Saccharification of Plant Biomass

“…The flasks were then incubated in a rotary incubator at 200 rpm at 37°C. Various parameters, such as pH (4)(5)(6)(7)(8), temperature (16-42°C), effect of time of induction (1-7 h), and effect of different IPTG concentrations (0.1 to 0.6 mM) were studied for the optimum production of the xylanase enzyme.…”

“…Two main families of glycosyl hydrolases, family 10 and family 11, represent the endoxylanases, categorized on the basis of their sequence similarities and hydrophobic cluster analysis [8]. These two families of endoxylanases are further differentiated on the bases of their molecular weights, e.g., family 10 comprises endoxylanases of larger molecular weights higher than 40 kDa and family 11 belongs to endoxylanases with smaller molecular weights (<20 kDa).…”