Project description:Glycoside hydrolases (GHs), the enzymes that break glycosidic bonds, are ubiquitous in the ecosystem, where they perform a range of biological functions. As an interesting glycosidase family, Glycoside hydrolase family 97 (GH97) contains α-glucosidase, α-galactosidase, and glucoamylase. Only ten members of GH97 have been characterized so far. It is critical to explore novel members to elucidate the catalytic mechanism and application potential of GH97 family. In this study, a novel glucoamylase QsGH97a from Qipengyuania seohaensis SW-135 was cloned and expressed in E. coli. Sequence analysis and NMR results show that QsGH97a is classified into GH97a, and adopts inverting mechanism. The biochemical characterization indicates that QsGH97a shows the optimal activity at 50 °C and pH 8.0. Ca2+ has little effect on the catalytic activity; however, the activity can be substantially increased by 8-13 folds in the presence of Ba2+ or Sr2+. Additionally, the metal content of QsGH97a assay showed a high proportion of Sr2+. The specific metal activity was initially revealed in glucoamylases, which is not found in other members. These results imply that QsGH97a not only is a new member of GH97, but also has potential for industrial applications. Our study reveals that Ba2+ or Sr2+ may be involved in the catalytic mechanism of glucoamylase, laying the groundwork for a more complete knowledge of GH97 and its possible industrial application.
Project description:The α-glucosidases play indispensable roles in the metabolic mechanism of organism, prevention, and treatment of the disease, and sugar hydrolysis, and are widely used in chemical synthesis, clinical diagnosis, and other fields. However, improving their catalytic efficiency and production to meet commercial demand remains a huge challenge. Here we detected a novel GH13 family α-glucosidase, QsGH13, from the deep-sea bacterium Qipengyuania seohaensis sp. SW-135. QsGH13 is highly substrate specific and only hydrolyzes sugars containing alpha-1,4 glucoside bonds. For example, its enzymatic activity for p-nitrophenyl-α-D-glucopyranoside was 25.41 U/mg, and the K m value was 0.2952 ± 0.0322 mM. The biochemical results showed that the optimum temperature of QsGH13 is 45°C, the optimum pH is 10.0, and it has excellent biological characteristics such as alkali resistance and salt resistance. The crystal structure of QsGH13 was resolved with a resolution of 2.2 Å, where QsGH13 is composed of a typical TIM barrel catalytic domain A, a loop-rich domain B, and a conserved domain C. QsGH13 crystal belonged to the monoclinic space group P212121, with unit-cell parameters a = 58.816 Å, b = 129.920 Å, c = 161.307 Å, α = γ = β = 90°, which contains two monomers per asymmetric unit. The β → α loop 4 of QsGH13 was located above catalytic pocket. Typical catalytic triad residues Glu202, Asp266, and Glu329 were found in QsGH13. The biochemical properties and structural analysis of QsGH13 have greatly improved our understanding of the catalytic mechanism of GH13 family. This study provides new ideas to broaden the application of α-glucosidase in alcohol fermentation, glycolysis, and other industries.
Project description:A novel esterase gene, e69, was cloned from Erythrobacter seohaensis SW-135, which was isolated from a tidal flat sediment of the Yellow Sea in Korea. This gene is 825 bp in length and codes for a 29.54 kDa protein containing 274 amino acids. Phylogenetic analysis showed that E69 is a new member of the bacterial lipolytic enzyme family IV. This enzyme exhibited the highest level of activity toward p-nitrophenyl (NP) butyrate but little or no activity toward the other p-NP esters tested. The optimum temperature and pH of the catalytic activity of E69 were 60°C and pH 10.5, respectively. The enzyme exhibited stable activity over a wide range of alkaline pH values (7.5-9.5). In addition, E69 was found to be a halotolerant esterase as it exhibited the highest hydrolytic activity in the presence of 0.5 M NaCl and was still active in the presence of 3 M NaCl. Moreover, it possessed some degree of tolerance to Triton X-100 and several organic solvents. Through homology modeling and comparison with other esterases, it was suggested that the absence of the cap domain and its narrow substrate-binding pocket might be responsible for its narrow substrate specificity. Sequence and structural analysis results suggested that its high ratio of negatively to positively charged residues, large hydrophobic surface area, and negative electrostatic potential on the surface may be responsible for its alkaline adaptation. The results of this study provide insight into marine alkaliphilic esterases, and the unique properties of E69 make it a promising candidate as a biocatalyst for industrial applications.