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JXB Advance Access published online on January 6, 2009
Journal of Experimental Botany, doi:10.1093/jxb/ern333
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© The Author [2009]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

REVIEW-ARTICLE

Structural insights into glycoside hydrolase family 32 and 68 enzymes: functional implications

Willem Lammens1,2, Katrien Le Roy1, Lindsey Schroeven1, André Van Laere1, Anja Rabijns2 and Wim Van den Ende1,*

1Laboratorium voor Moleculaire Plantenfysiologie, Faculteit Wetenschappen, Departement Biologie, K. U. Leuven, Kasteelpark Arenberg 31, bus 2434, B-3001 Heverlee, Belgium
2Laboratorium voor Biokristallografie, Faculteit Farmaceutische Wetenschappen, K. U. Leuven, Herestraat 49, O&N II, bus 822, B-3000 Leuven, Belgium

* To whom correspondence should be addressed: E-mail: wim.vandenende{at}bio.kuleuven.be

Glycoside hydrolases (GH) have been shown to play unique roles in various biological processes like the biosynthesis of glycans, cell wall metabolism, plant defence, signalling, and the mobilization of storage reserves. To date, GH are divided into more than 100 families based upon their overall structure. GH32 and GH68 are combined in clan GH-J, not only harbouring typical hydrolases but also non-Leloir type transferases (fructosyltransferases), involved in fructan biosynthesis. This review summarizes the recent structure–function research progress on plant GH32 enzymes, and highlights the similarities and differences compared with the microbial GH32 and GH68 enzymes. A profound analysis of ligand-bound structures and site-directed mutagenesis experiments identified key residues in substrate (or inhibitor) binding and recognition. In particular, sucrose can bind as inhibitor in Cichorium intybus 1-FEH IIa, whereas it binds as substrate in Bacillus subtilis levansucrase and Arabidopsis thaliana cell wall invertase (AtcwINV1). In plant GH32, a single residue, the equivalent of Asp239 in AtcwINV1, appears to be important for sucrose stabilization in the active site and essential in determining sucrose donor specificity.

Key words: β-fructosidase, clan GH-J, exo-inulinase, fructan exohydrolase, glycoside hydrolase family 32, glycoside hydrolase family 68, invertase, levansucrase

Received 9 October 2008; Revised 21 November 2008 Accepted 25 November 2008


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