3GZK

Crystal structures of A. acidocaldarius endoglucanase Cel9A in complex with cello-oligosaccharides: strong -1 and -2 subsites mimic cellobiohydrolase activity

(2009) J Mol Biol 394: 61-70

• PubMed: 19729024 Search on PubMed
• DOI: https://doi.org/10.1016/j.jmb.2009.08.060
• Primary Citation of Related Structures:  
  3GZK, 3H2W, 3H3K


• PubMed Abstract: 
  

  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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Organizational Affiliation: 

Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.