TY - JOUR
T1 - Xyloglucan is recognized by carbohydrate-binding modules that interact with β-glucan chains
AU - Najmudin, Shabir
AU - Guerreiro, Catarina I. P. D.
AU - Carvalho, Ana L.
AU - Prates, José A. M.
AU - Correia, Márcia A. S.
AU - Alves, Victor D.
AU - Ferreira, Luís M. A.
AU - Romão, Maria J.
AU - Gilbert, Harry J.
AU - Bolam, David N.
AU - Fontes, Carlos M. G. A.
N1 - Biotechnology and Biological Sciences Research Council
(BB/C005074/1)
PY - 2006/3/31
Y1 - 2006/3/31
N2 - Enzyme systems that attack the plant cell wall contain noncatalytic carbohydrate-binding modules (CBMs) that mediate attachment to this composite structure and play a pivotal role in maximizing the hydrolytic process. Although xyloglucan, which includes a backbone of β-1,4-glucan decorated primarily with xylose residues, is a key component of the plant cell wall, CBMs that bind to this polymer have not been identified. Here we showed that the C-terminal domain of the modular Clostridium thermocellum enzyme CtCel9D-Cel44A (formerly known as CelJ) comprises a novel CBM (designated CBM44) that binds with equal affinity to cellulose and xyloglucan. We also showed that accommodation of xyloglucan side chains is a general feature of CBMs that bind to single cellulose chains. The crystal structures of CBM44 and the other CBM (CBM30) in CtCel9D-Cel44A display a β-sandwich fold. The concave face of both CBMs contains a hydrophobic platform comprising three tryptophan residues that can accommodate up to five glucose residues. The orientation of these aromatic residues is such that the bound ligand would adopt the twisted conformation displayed by cello-oligosaccharides in solution. Mutagenesis studies confirmed that the hydrophobic platform located on the concave face of both CBMs mediates ligand recognition. In contrast to other CBMs that bind to single polysaccharide chains, the polar residues in the binding cleft of CBM44 play only a minor role in ligand recognition. The mechanism by which these proteins are able to recognize linear and decorated β-1,4-glucans is discussed based on the structures of CBM44 and the other CBMs that bind single cellulose chains.
AB - Enzyme systems that attack the plant cell wall contain noncatalytic carbohydrate-binding modules (CBMs) that mediate attachment to this composite structure and play a pivotal role in maximizing the hydrolytic process. Although xyloglucan, which includes a backbone of β-1,4-glucan decorated primarily with xylose residues, is a key component of the plant cell wall, CBMs that bind to this polymer have not been identified. Here we showed that the C-terminal domain of the modular Clostridium thermocellum enzyme CtCel9D-Cel44A (formerly known as CelJ) comprises a novel CBM (designated CBM44) that binds with equal affinity to cellulose and xyloglucan. We also showed that accommodation of xyloglucan side chains is a general feature of CBMs that bind to single cellulose chains. The crystal structures of CBM44 and the other CBM (CBM30) in CtCel9D-Cel44A display a β-sandwich fold. The concave face of both CBMs contains a hydrophobic platform comprising three tryptophan residues that can accommodate up to five glucose residues. The orientation of these aromatic residues is such that the bound ligand would adopt the twisted conformation displayed by cello-oligosaccharides in solution. Mutagenesis studies confirmed that the hydrophobic platform located on the concave face of both CBMs mediates ligand recognition. In contrast to other CBMs that bind to single polysaccharide chains, the polar residues in the binding cleft of CBM44 play only a minor role in ligand recognition. The mechanism by which these proteins are able to recognize linear and decorated β-1,4-glucans is discussed based on the structures of CBM44 and the other CBMs that bind single cellulose chains.
UR - http://www.scopus.com/inward/record.url?scp=33646840847&partnerID=8YFLogxK
U2 - 10.1074/jbc.M510559200
DO - 10.1074/jbc.M510559200
M3 - Article
C2 - 16314409
AN - SCOPUS:33646840847
VL - 281
SP - 8815
EP - 8828
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 13
ER -