Abstract
The high resolution (1.2-1.4 ?) complex three-dimensional structures of xylanase (family 11) provide the xylooligosaccharide substrates binding information by X-ray crystallography. The electron density of xylohexaose from two xylotriose show GH-11 xylanase have glycosyltransferase activity in the xylotriose soaking data. It is the first time to capture that the 6 subsites abound with substrates. Arg122 changed the orientation to offer a hydrogen bond to fix xylooligosaccharides in the catalytic site. Other residues were close to the catalytic pocket also form hydrogen bonds to stabilize the substrates. W18, Y179 and Y96 interact with the xylopyranose rings by aromatic stacking at the subsite (-2,+2 and +3) to recognize substrate binding actions. Two glutamic acids, Glu86 and Glu177 are a nucleophile (base) and a proton donor (acid), interact with substrates at subsite (-1) to build up a glycosidic bond to connect two xylotriose sugars. Other complex structure datas confirm previous reports. The structural information can explain the GH-11 xylanase kinetic data and offer a direction to improve the specify activity, heat tolerant and glycosynthase activity.