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From Proteopedia
Xyloglucan endotransglycosylase in complex with the xyloglucan nonasaccharide XLLG.
Structural highlights
FunctionXTH34_POPPZ Catalyzes xyloglucan endotransglycosylation (XET). Cleaves and religates xyloglucan polymers (PubMed:12595718, PubMed:15020748, PubMed:16014999, PubMed:15804235, PubMed:15125664). Does not catalyze xyloglucan endohydrolysis (XEH) (PubMed:15804235). Involved in early phases of secondary (S) cell wall formation in fibers of the xylem and phloem vascular tissues of wood stems. May play a role in restructuring primary cell walls, possibly creating and reinforcing the connections between the primary and S cell wall layers (PubMed:12468728). Functions in the gelatinous (G) layers of the tension wood fibers that are involved in bending of the wood stems. May play a role in G fiber shrinking by repairing broken xyloglucan cross-links between G and S2 cell wall layers via its XET activity to maintain connections between the layers (PubMed:17504814).[1] [2] [3] [4] [5] [6] [7] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedXyloglucan endotransglycosylases (XETs) cleave and religate xyloglucan polymers in plant cell walls via a transglycosylation mechanism. Thus, XET is a key enzyme in all plant processes that require cell wall remodeling. To provide a basis for detailed structure-function studies, the crystal structure of Populus tremula x tremuloides XET16A (PttXET16A), heterologously expressed in Pichia pastoris, has been determined at 1.8-A resolution. Even though the overall structure of PttXET16A is a curved beta-sandwich similar to other enzymes in the glycoside hydrolase family GH16, parts of its substrate binding cleft are more reminiscent of the distantly related family GH7. In addition, XET has a C-terminal extension that packs against the conserved core, providing an additional beta-strand and a short alpha-helix. The structure of XET in complex with a xyloglucan nonasaccharide, XLLG, reveals a very favorable acceptor binding site, which is a necessary but not sufficient prerequisite for transglycosylation. Biochemical data imply that the enzyme requires sugar residues in both acceptor and donor sites to properly orient the glycosidic bond relative to the catalytic residues. Crystal structures of a poplar xyloglucan endotransglycosylase reveal details of transglycosylation acceptor binding.,Johansson P, Brumer H 3rd, Baumann MJ, Kallas AM, Henriksson H, Denman SE, Teeri TT, Jones TA Plant Cell. 2004 Apr;16(4):874-86. Epub 2004 Mar 12. PMID:15020748[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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