The Location of the Ligand-binding Site of Carbohydrate-binding Modules That Have Evolved from a Common Sequence Is Not Conserved

Czjzek, Mirjam, Bolam, David N., Mosbah, Amor, Allouch, Julie, Fontes, Carlos, Ferreira, Luis, Bornet, Olivier, Zamboni, Véronique, Darbon, Hervé, Smith, Nicola L., Black, Gary, Henrissat, Bernard and Gilbert, Harry J. (2001) The Location of the Ligand-binding Site of Carbohydrate-binding Modules That Have Evolved from a Common Sequence Is Not Conserved. The Journal of Biological Chemistry, 276 (51). pp. 48580-48587. ISSN 0021-9258

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Abstract

Polysaccharide-degrading enzymes are generally modular proteins that contain non-catalytic carbohydrate-binding modules (CBMs), which potentiate the activity of the catalytic module. CBMs have been grouped into sequence-based families, and three-dimensional structural data are available for half of these families. Clostridium thermocellum xylanase 11A is a modular enzyme that contains a CBM from family 6 (CBM6), for which no structural data are available. We have determined the crystal structure of this module to a resolution of 2.1 Å. The protein is a β-sandwich that contains two potential ligand-binding clefts designated cleft A and B. The CBM interacts primarily with xylan, and NMR spectroscopy coupled with site-directed mutagenesis identified cleft A, containing Trp-92, Tyr-34, and Asn-120, as the ligand-binding site. The overall fold of CBM6 is similar to proteins in CBM families 4 and 22, although surprisingly the ligand-binding site in CBM4 and CBM22 is equivalent to cleft B in CBM6. These structural data define a superfamily of CBMs, comprising CBM4, CBM6, and CBM22, and demonstrate that, although CBMs have evolved from a relatively small number of ancestors, the structural elements involved in ligand recognition have been assembled at different locations on the ancestral scaffold.

Item Type:	Article
Subjects:	C700 Molecular Biology, Biophysics and Biochemistry
Department:	Faculties > Health and Life Sciences > Applied Sciences
Depositing User:	Becky Skoyles
Date Deposited:	12 Feb 2015 14:44
Last Modified:	12 Oct 2019 17:29
URI:	http://nrl.northumbria.ac.uk/id/eprint/19346

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