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The thermostable endo‐1,5‐α‐l‐arabinanase from Bacillus thermodenitrificans TS‐3 (ABN‐TS) hydrolyzes the α‐1,5‐l‐arabinofuranoside linkages of arabinan. In this study, the crystal structures of inactive ABN‐TS mutants, D27A and D147N, were determined in complex with arabino‐oligosaccharides. The crystal structures revealed that ABN‐TS has at least six subsites in the deep V‐shaped cleft formed across one face of the propeller structure. The structural features indicate that substrate recognition is profoundly influenced by the remote subsites as well as by the subsites surrounding the active center. The 'open' structure of the substrate‐binding cleft of the endo‐acting ABN‐TS is suitable for the random binding of several sugar units in polymeric substrates. Crystal structures of D27A and D147N mutants of the endo‐1,5‐α‐l‐arabinanase from Bacillus thermodenitrificans TS‐3 in complex with arabinohexaose were determined. [ABSTRACT FROM AUTHOR]

The article discusses a study on the high-resolution structure of exo-arabinanase from Penicillium chrysogenum. The authors state that crystallization conditions giving high-quality crystals of Abnx were established successfully by what they call the novel technique referred to as COLAS. They also say that the structures presented in the article could reveal that Abnx has different mechanisms to funnel substrates to the active site and/or to stabilize the transition state compared with the arabinan-degrading enzyme Arb93A.

The crystal structure of a thermostable endo-1,5-alpha-L-arabinanase, ABN-TS, from Bacillus thermodenitrificans TS-3 was determined at 1.9 A to an R-factor of 18.3% and an R-free-factor of 22.5%. The enzyme molecule has a five-bladed beta-propeller fold. The substrate-binding cleft formed across one face of the propeller is open on both sides to allow random binding of several sugar units in the polymeric substrate arabinan. The beta-propeller fold is stabilized through a ring closure. ABN-TS exhibits a new closure-mode involving residues in the N-terminal region: Phe7 to Gly21 exhibit hydrogen bonds and hydrophobic interactions with the first and last blades, and Phe4 links the second and third blades through a hydrogen bond and an aromatic stacking interaction, respectively. The role of the N-terminal region in the thermostability was confirmed with a mutant lacking 16 amino acid residues from the N-terminus of ABN-TS.