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. 2010 Jun;153(2):456-66.
doi: 10.1104/pp.110.156844. Epub 2010 Apr 26.

The XTH gene family: an update on enzyme structure, function, and phylogeny in xyloglucan remodeling

Jens M Eklöf  1 , Harry Brumer
Affiliations

The XTH gene family: an update on enzyme structure, function, and phylogeny in xyloglucan remodeling

Jens M Eklöf et al. Plant Physiol. 2010 Jun.
No abstract available

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Figures

Figure 1.
Figure 1.
The evolution of GH16 and grouping of XTH genes in publicly available plant genomes. A, The proposed evolution of clan B containing GH7 and GH16 (updated from Michel et al. [2001]). B, A simplified tree showing the genome representatives of the Plantae (top) and a diagram showing the distribution of XTH genes into groups (bottom), with the number of genes from each organism at the top of each column (only XTH genes predicted to encode functional XTH gene products [i.e. containing a complete active-site motif] are included). The groups are colored as follows: group 1, black; group II, light gray; group III-A, white; group III-B, dark gray. The Chlorophyta are represented by the genomes of Chlamydomonas reinhardtii (http://phytozome.org/), Micromonas pusilla (Worden et al., 2009), Ostreococcus tauri (Derelle et al., 2006), and Ostreococcus lucimarinus (Palenik et al., 2007). All other genome data are available via http://www.phytozome.org/ (accessed March 2010).
Figure 2.
Figure 2.
Structures of XTH gene products and a closely related GH16 β-1,3;1,4-glucanase. A, Surface representation of PttXET16-34 (PDB ID 1un1, 1umz) in silver (C-terminal extension in copper) with XLLGXLLG octadecasaccharide bound (glucosyl backbone in blue and xylosyl and galactosyl units in gold; based on data from Mark et al. [2009]). B, Surface representation of a β-1,3;1,4-glucanase in silver, with the loop narrowing the negative subsites in copper (PDB ID 1u0a). C, Cartoon of PttXET16-34 showing the structure of the C-terminal extension (copper) and the catalytic amino acids (green) with a bound XLLGXLLG octadecasaccharide. D, Overlay of a XET, PttXET16-34 (silver with red loops), and an XEH, TmNXG1 (gold with blue loops; PDB ID 2uwa, 2vh9).
Figure 3.
Figure 3.
A schematic representation of the mechanism used by XETs and XEHs. Left, xyloglucan binds to XETs and XEHs in both negative and positive subsites (glucosyl units of xyloglucan in blue and xylosyl units in orange; subsite nomenclature of Davies et al. [1997]). After binding, the substrate is cleaved, resulting in a covalent glycosyl-enzyme intermediate (bond indicated in red). Right, in the last step, the glycosyl-enzyme is broken down by an incoming acceptor, either water (XEH activity) or the nonreducing end of a xyloglucan molecule (XET activity).
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