4d5q | pdb_00004d5q
Hypocrea jecorina Cel7A (wild type) soaked with xylopentaose.
Structural highlights
Function[GUX1_HYPJE] The biological conversion of cellulose to glucose generally requires three types of hydrolytic enzymes: (1) Endoglucanases which cut internal beta-1,4-glucosidic bonds; (2) Exocellobiohydrolases that cut the dissaccharide cellobiose from the non-reducing end of the cellulose polymer chain; (3) Beta-1,4-glucosidases which hydrolyze the cellobiose and other short cello-oligosaccharides to glucose. Publication Abstract from PubMedThe filamentous fungus Hypocrea jecorina (anamorph to Trichoderma reesei) is the predominant source of enzymes for industrial saccharification of lignocellulose biomass. The major enzyme, cellobiohydrolase Cel7A, constitutes nearly half of the total protein in the secretome. The performance of the enzymes is susceptible to inhibition by compounds liberated by physico-chemical pretreatment if the biomass is kept unwashed. Xylan and xylooligosaccharides (XOS) have been proposed to play a key role for inhibition of cellobiohydrolases of glycoside hydrolase family 7. To elucidate the mechanism behind this inhibition at a molecular level, we have used X-ray crystallography to determine structures of H. jecorina Cel7A in complex with XOS. Structures with xylotriose, -tetraose, and -pentaose, reveal a predominant binding mode at the beginning of the substrate-binding tunnel of the enzyme, where each xylose residue is shifted about 2.4 A towards the catalytic center compared to the binding of cellooligosaccharides. Furthermore, partial occupancy of two consecutive xylose residues in subsites -2 and -1 suggests an alternate binding mode for XOS in the vicinity of the catalytic center. Interestingly, the -1 xylosyl unit exhibits an open aldehyde conformation in one of the structures and a regular ring-closed pyranoside in another complex. Complementary inhibition studies with p-nitrophenyl lactoside as substrate indicate mixed inhibition rather than pure competitive inhibition. This article is protected by copyright. All rights reserved. Structural insights into the inhibition of Cellobiohydrolase Cel7A by xylooligosaccharides.,Haddad Momeni M, Ubhayasekera W, Sandgren M, Stahlberg J, Hansson H FEBS J. 2015 Mar 12. doi: 10.1111/febs.13265. PMID:25765184[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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