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J Biol Chem. 2007 Apr 20;282(16):12066-74. Epub 2007 Feb 23.

A tomato endo-beta-1,4-glucanase, SlCel9C1, represents a distinct subclass with a new family of carbohydrate binding modules (CBM49).

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1
Department of Plant Biology, Cornell Theory Center, Cornell University, Ithaca, New York 14853, USA.

Abstract

A critical structural feature of many microbial endo-beta-1,4-glucanases (EGases, or cellulases) is a carbohydrate binding module (CBM), which is required for effective crystalline cellulose degradation. However, CBMs are absent from plant EGases that have been biochemically characterized to date, and accordingly, plant EGases are not generally thought to have the capacity to degrade crystalline cellulose. We report the biochemical characterization of a tomato EGase, Solanum lycopersicum Cel8 (SlCel9C1), with a distinct C-terminal noncatalytic module that represents a previously uncharacterized family of CBMs. In vitro binding studies demonstrated that this module indeed binds to crystalline cellulose and can similarly bind as part of a recombinant chimeric fusion protein containing an EGase catalytic domain from the bacterium Thermobifida fusca. Site-directed mutagenesis studies show that tryptophans 559 and 573 play a role in crystalline cellulose binding. The SlCel9C1 CBM, which represents a new CBM family (CBM49), is a defining feature of a new structural subclass (Class C) of plant EGases, with members present throughout the plant kingdom. In addition, the SlCel9C1 catalytic domain was shown to hydrolyze artificial cellulosic polymers, cellulose oligosaccharides, and a variety of plant cell wall polysaccharides.

PMID:
17322304
DOI:
10.1074/jbc.M607925200
[Indexed for MEDLINE]
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