4BA6

High Resolution structure of the C-terminal family 65 Carbohydrate Binding Module (CBM65B) of endoglucanase Cel5A from Eubacterium cellulosolvens

Summary for 4BA6

• Entry DOI: 10.2210/pdb4ba6/pdb
• Related: 2YPJ 4AEK 4AEM 4AFD 4AFM
• Descriptor: Endoglucanase cel5A, GLYCEROL (3 entities in total)
• Functional Keywords: carbohydrate-binding protein, plant cell wall degradation, beta-jelly roll
• Biological source: Eubacterium cellulosolvens
• Total number of polymer chains: 1
• Total formula weight: 16065.66

Authors

Venditto, I.,Luis, A.S.,Basle, A.,Temple, M.,Ferreira, L.M.A.,Fontes, C.M.G.A.,Gilbert, H.J.,Najmudin, S. (deposition date: 2012-09-11, release date: 2012-12-19, Last modification date: 2023-12-20)

Primary citation

Luis, A.S.,Venditto, I.,Temple, M.J.,Rogowski, A.,Basle, A.,Xue, J.,Knox, J.P.,Prates, J.A.,Ferreira, L.M.,Fontes, C.M.,Najmudin, S.,Gilbert, H.J.
Understanding how noncatalytic carbohydrate binding modules can display specificity for xyloglucan.
J. Biol. Chem., 288:4799-4809, 2013

PubMed Abstract: Plant biomass is central to the carbon cycle and to environmentally sustainable industries exemplified by the biofuel sector. Plant cell wall degrading enzymes generally contain noncatalytic carbohydrate binding modules (CBMs) that fulfil a targeting function, which enhances catalysis. CBMs that bind β-glucan chains often display broad specificity recognizing β1,4-glucans (cellulose), β1,3-β1,4-mixed linked glucans and xyloglucan, a β1,4-glucan decorated with α1,6-xylose residues, by targeting structures common to the three polysaccharides. Thus, CBMs that recognize xyloglucan target the β1,4-glucan backbone and only accommodate the xylose decorations. Here we show that two closely related CBMs, CBM65A and CBM65B, derived from EcCel5A, a Eubacterium cellulosolvens endoglucanase, bind to a range of β-glucans but, uniquely, display significant preference for xyloglucan. The structures of the two CBMs reveal a β-sandwich fold. The ligand binding site comprises the β-sheet that forms the concave surface of the proteins. Binding to the backbone chains of β-glucans is mediated primarily by five aromatic residues that also make hydrophobic interactions with the xylose side chains of xyloglucan, conferring the distinctive specificity of the CBMs for the decorated polysaccharide. Significantly, and in contrast to other CBMs that recognize β-glucans, CBM65A utilizes different polar residues to bind cellulose and mixed linked glucans. Thus, Gln(106) is central to cellulose recognition, but is not required for binding to mixed linked glucans. This report reveals the mechanism by which β-glucan-specific CBMs can distinguish between linear and mixed linked glucans, and show how these CBMs can exploit an extensive hydrophobic platform to target the side chains of decorated β-glucans.

PubMed: 23229556
DOI: 10.1074/jbc.M112.432781

Experimental method

X-RAY DIFFRACTION (1.42 Å)