7cbd | pdb_00007cbd
Catalytic domain of Cellulomonas fimi Cel6B
Structural highlights
FunctionGUXA_CELFA This enzyme hydrolyzes 1,4-beta-D-glucosidic linkages of cellulose. Weak activity against carboxymethylcellulose, bacterial microcrystalline cellulose and barley beta-glucan. Has also weak endoglucanase activity. Hydrolyzes glucosidic bonds with inversion of anomeric configuration. Publication Abstract from PubMedCellobiohydrolases directly convert crystalline cellulose into cellobiose and are of biotechnological interest to achieve efficient biomass utilization. As a result, much research in the field has focused on identifying cellobiohydrolases that are very fast. Cellobiohydrolase A from the bacterium Cellulomonas fimi (CfCel6B) and cellobiohydrolase II from the fungus Trichoderma reesei (TrCel6A) have similar catalytic domains (CDs) and show similar hydrolytic activity. However, TrCel6A and CfCel6B have different cellulose-binding domains (CBDs) and linkers: TrCel6A has a glycosylated peptide linker, whereas CfCel6B's linker consists of three fibronectin type 3 domains. We previously found that TrCel6A's linker plays an important role in increasing the binding rate constant to crystalline cellulose. However, it was not clear whether CfCel6B's linker has similar function. Here we analyze kinetic parameters of CfCel6B using single-molecule fluorescence imaging to compare CfCel6B and TrCel6A. We find that CBD is important for initial binding of CfCel6B, but the contribution of the linker to the binding rate constant or to the dissociation rate constant is minor. The crystal structure of the CfCel6B CD showed longer loops at the entrance and exit of the substrate-binding tunnel compared with TrCel6A CD, which results in higher processivity. Furthermore, CfCel6B CD showed not only fast surface diffusion but also slow processive movement, which is not observed in TrCel6A CD. Combined with the results of a phylogenetic tree analysis, we propose that bacterial cellobiohydrolases are designed to degrade crystalline cellulose using high-affinity CBD and high-processivity CD. Domain architecture divergence leads to functional divergence in binding and catalytic domains of bacterial and fungal cellobiohydrolases.,Nakamura A, Ishiwata D, Visootsat A, Uchiyama T, Mizutani K, Kaneko S, Murata T, Igarashi K, Iino R J Biol Chem. 2020 Oct 23;295(43):14606-14617. doi: 10.1074/jbc.RA120.014792. Epub, 2020 Aug 18. PMID:32816991[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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