CONICET | Buscador de Institutos y Recursos Humanos

The Arabidopsis thaliana genome codifies for the xylanase (RefSeq=NP_176133) AtXyn1, which is predominantly expressed in vascular bundles, but not in vessel cells (1). Like many polysaccharide-degrading enzymes AtXyn1 displays a modular structure in which a catalytic domain (C-terminal) is attached to three in tandem non-catalytic modules (2). Those modules where classified in the family 22 (previously family 4_9) of carbohydrate binding modules (CBM) (http://www.cazy.org/CBM22.html), according to sequence similarity (1). Strikingly, it shows the same modular organization than Starch Synthase III (SeqRef: NP_172637.1) from Arabidopsis, previously characterized in our laboratory, which is also capable to bind xylanes, among others carbohydrates (3). The Clostridium thermocellum xylanase (XylY) (UniProt=XYNY_CLOTM) 3D structure is available, showing two CBMs classified in the family 22, shearing a 17% of identity (residues 4-160) with the module Xyl2 from AtXyn1. Although there is a sequence classification of this modules, we introduce an homology model of Xyl1, Xyl2 and Xyl3 that was built by using the crystallographic structure of XylY (PDB= 1H6Y), achieving a good quality model, consisting in a β-sandwich (classic β -jelly roll) with a shallow surface groove that forms the xylotetraose-binding site (2).References:1. Suzuki, M., Kato, A., Nagata, N., and Komeda, Y. (2002). Plant Cell Physiol 43, 759-767.2. Charnock, S. , Bolam, D., Turkenburg, J. P., Gilbert, H. J., Ferreira, L. M., Davies, G. J., and Fontes, C. M. (2000). Biochemistry 39, 5013-5021.3. Palopoli, N., Busi, M. V., Fornasari, M. S., Gomez-Casati, D., Ugalde, R., and Parisi, G. (2006). Proteins 65, 27-31.