Project description:The acetylxylan esterases (AXEs) classified into carbohydrate esterase family 4 (CE4) are metalloenzymes that catalyze the deacetylation of acetylated carbohydrates. AXE from Caldanaerobacter subterraneus subsp. tengcongensis (TTE0866), which belongs to CE4, is composed of three parts: a signal sequence (residues 1-22), an N-terminal region (NTR; residues 23-135) and a catalytic domain (residues 136-324). TTE0866 catalyzes the deacetylation of highly substituted cellulose acetate and is expected to be useful for industrial applications in the reuse of resources. In this study, the crystal structure of TTE0866 (residues 23-324) was successfully determined. The crystal diffracted to 1.9 Å resolution and belonged to space group I212121. The catalytic domain (residues 136-321) exhibited a (β/α)7-barrel topology. However, electron density was not observed for the NTR (residues 23-135). The crystal packing revealed the presence of an intermolecular space without observable electron density, indicating that the NTR occupies this space without a defined conformation or was truncated during the crystallization process. Although the active-site conformation of TTE0866 was found to be highly similar to those of other CE4 enzymes, the orientation of its Trp264 side chain near the active site was clearly distinct. The unique orientation of the Trp264 side chain formed a different-shaped cavity within TTE0866, which may contribute to its reactivity towards highly substituted cellulose acetate.
Project description:Caldanaerobacter subterraneus subsp. keratinolyticus subsp. nov. strain KAk was isolated from a geothermal hot spring located in Kazakhstan. Growth occurred at temperatures ranging from 50 to 80 °C, with approximately 70 °C as optimum. It also thrived in pH conditions ranging from 4.0 to 9.0, with the best growth occurring at 6.8. Under optimal conditions in a glucose-containing medium, the cells were predominantly observed singly, in pairs, or less frequently in chains, and did not form endospores. However, under conditions involving growth with merino wool or feathers, or under suboptimal conditions, the cells of strain KAk exhibited a notably elongated and thinner morphology, with lengths ranging from 5 to 8 µm, and spores were observed. The KAk strain exhibited efficient degradation of feather keratin and merino wool at temperatures ranging from 65 to 70 °C. Analysis of the 16S rRNA gene sequence placed KAk within the genus Caldanaerobacter, family Thermoanaerobacteraceae, with the highest similarity to C. subterraneus subsp. tengcongensis MB4T (98.84% sequence identity). Furthermore, our analysis of the draft genome sequence indicated a genome size of 2.4 Mbp, accompanied by a G+C value of 37.6 mol%. This study elucidated the physiological and genomic characteristics of strain KAk, highlighting its keratinolytic capabilities and distinctiveness compared to other members of the genus Caldanaerobacter.
Project description:Acetylxylan esterase from Caldanaerobacter subterraneus subsp. tengcongensis (TTE0866) has an N-terminal region (NTR; residues 23-135) between the signal sequence (residues 1-22) and the catalytic domain (residues 136-324), which is of unknown function. Our previous study revealed the crystal structure of the wild-type (WT) enzyme containing the NTR and the catalytic domain. Although the structure of the catalytic domain was successfully determined, that of the NTR was undetermined, as its electron density was unclear. In this study, we investigated the role of the NTR through functional and structural analyses of NTR truncation mutants. Based on sequence and secondary structure analyses, NTR was confirmed to be an intrinsically disordered region. The truncation of NTR significantly decreased the solubility of the proteins at low salt concentrations compared with that of the WT. The NTR-truncated mutant easily crystallized in a conventional buffer solution. The crystal exhibited crystallographic properties comparable with those of the WT crystals suitable for structural determination. These results suggest that NTR plays a role in maintaining the solubility and inhibiting the crystallization of the catalytic domain.
Project description:Two novel genes encoding for heat and solvent stable lipases from strictly anaerobic extreme thermophilic bacteria Thermoanaerobacter thermohydrosulfuricus (LipTth) and Caldanaerobacter subterraneus subsp. tengcongensis (LipCst) were successfully cloned and expressed in E. coli. Recombinant proteins were purified to homogeneity by heat precipitation, hydrophobic interaction, and gel filtration chromatography. Unlike the enzymes from mesophile counterparts, enzymatic activity was measured at a broad temperature and pH range, between 40 and 90 degrees C and between pH 6.5 and 10; the half-life of the enzymes at 75 degrees C and pH 8.0 was 48 h. Inhibition was observed with 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride and phenylmethylsulfonylfluorid indicating that serine and thiol groups play a role in the active site of the enzymes. Gene sequence comparisons indicated very low identity to already described lipases from mesophilic and psychrophilic microorganisms. By optimal cultivation of E. coli Tuner (DE3) cells in 2-l bioreactors, a massive production of the recombinant lipases was achieved (53-2200 U/l) Unlike known lipases, the purified robust proteins are resistant against a large number of organic solvents (up to 99%) and detergents, and show activity toward a broad range of substrates, including triacylglycerols, monoacylglycerols, esters of secondary alcohols, and p-nitrophenyl esters. Furthermore, the enzyme from T. thermohydrosulfuricus is suitable for the production of optically pure compounds since it is highly S-stereoselective toward esters of secondary alcohols. The observed E values for but-3-yn-2-ol butyrate and but-3-yn-2-ol acetate of 21 and 16, respectively, make these enzymes ideal candidates for kinetic resolution of synthetically useful compounds.
Project description:The project was designed to explore biological rhythms in the hydrothermal vent mussel Bathymodiolus azoricus. The experiment provides the first high-resolution temporal transcriptomes of an hydrothermal species, both in situ and in the laboratory. For each condition, 5 mussels were sampled every 2h 4min for 24h 48min.