3H3K image
Entry Detail
PDB ID:
3H3K
Keywords:
Title:
Structure of A. acidocaldarius cellulase CelA in complex with cellotetraose
Biological Source:
Host Organism:
PDB Version:
Deposition Date:
2009-04-16
Release Date:
2009-10-13
Method Details:
Experimental Method:
Resolution:
2.10 Å
R-Value Free:
0.21
R-Value Work:
0.18
R-Value Observed:
0.18
Space Group:
P 21 21 2
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Cellulase
Chain IDs:A
Chain Length:537
Number of Molecules:1
Biological Source:Alicyclobacillus acidocaldarius
Primary Citation
Crystal structures of A. acidocaldarius endoglucanase Cel9A in complex with Cello-oligosaccharides: strong -1 and -2 subsites mimic cellobiohydrolase activity
J.Mol.Biol. 394 61 70 (2009)
PMID: 19729024 DOI: 10.1016/j.jmb.2009.08.060

Abstact

Alicyclobacillus acidocaldarius endoglucanase Cel9A (AaCel9A) is an inverting glycoside hydrolase with beta-1,4-glucanase activity on soluble polymeric substrates. Here, we report three X-ray structures of AaCel9A: a ligand-free structure at 1.8 A resolution and two complexes at 2.66 and 2.1 A resolution, respectively, with cellobiose obtained by co-crystallization and with cellotetraose obtained by the soaking method. AaCel9A forms an (alpha/alpha)(6)-barrel like other glycoside hydrolase family 9 enzymes. When cellobiose is used as a ligand, three glucosyl binding subsites are occupied, including two on the glycone side, while with cellotetraose as a ligand, five subsites, including four on the glycone side, are occupied. A structural comparison showed no conformational rearrangement of AaCel9A upon ligand binding. The structural analysis demonstrates that of the four minus subsites identified, subsites -1 and -2 show the strongest interaction with bound glucose. In conjunction with the open active-site cleft of AaCel9A, this is able to reconcile the previously observed cleavage of short-chain oligosaccharides with cellobiose as main product with the endo mode of action on larger polysaccharides.

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