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Three‐dimensional structure of endo‐1,4‐beta‐xylanase II from Trichoderma reesei: two conformational states in the active site.
Author(s) -
Törrönen A.,
Harkki A.,
Rouvinen J.
Publication year - 1994
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1994.tb06536.x
Subject(s) - trichoderma reesei , antiparallel (mathematics) , chemistry , stereochemistry , crystallography , physics , biochemistry , enzyme , cellulase , quantum mechanics , magnetic field
The three‐dimensional structure of endo‐1,4‐beta‐xylanase II (XYNII) from Trichoderma reesei has been determined by X‐ray diffraction techniques and refined to a conventional R‐factor of 18.3% at 1.8 A resolution. The 190 amino acid length protein was found to exist as a single domain where the main chain folds to form two mostly antiparallel beta‐sheets, which are packed against each other in parallel. The beta‐sheet structure is twisted, forming a large cleft on one side of the molecule. The structure of XYNII resembles that of Bacillus 1,3‐1,4‐beta‐glucanase. The cleft is an obvious suggestion for an active site, which has putative binding sites for at least four xylose residues. The catalytic residues are apparently the two glutamic acid residues (Glu86 and Glu177) in the middle of the cleft. One structure was determined at pH 5.0, corresponding to the pH optimum of XYNII. The second structure was determined at pH 6.5, where enzyme activity is reduced considerably. A clear structural change was observed, especially in the position of the side chain of Glu177. The observed conformational change is probably important for the mechanism of catalysis in XYNII.