mRNA secondary structure engineering of Thermobifida fusca endoglucanase (Cel6A) for enhanced expression in Escherichia coli

Characterization and synergistic activity of heterologously expressed microbial-derived endoglucanase and bifunctional cellulase on wheat straw

Cellulases are divided into endoglucanase, exoglucanase, and β-glucosidase based on their catalytic activity. Eight cellulases were recombinantly expressed in Escherichia coli BL21 to investigate their effects on the enzymatic hydrolysis of wheat straw. Among them, cellulase 2006 exhibited the highest endoglucanase activity (432.25 U/mg), while Bf1 displayed superior exoglucanase and β-glucosidase activities (577.46 and 1991.63 U/mg respectively). Bioinformatic and enzymatic analyses revealed that both cellulases displayed notable thermal and pH stability. The enzyme kinetics parameters revealed that Km values for cellulases 2006 and Bf1 were 15.98 and 14.19 mg/mL, respectively, with Vmax values of 20.78 and 16.38 μmol/min/mg. In a prokaryotic co-expression system, the mixed cellulase Bf2006 exhibited endoglucanase, exoglucanase, and β-glucosidase activities (130.78, 1406.36, and 1119.25 U/mg, respectively). The enzymatic hydrolysis assay revealed that these three cellulases acted on the cellulose macromolecules in wheat straw, increasing reducing sugar content and decreasing crystallinity. Endoglucanase 2006 acted on various organic compounds rich in phenols and aromatic heterocycles, while Bf1 primarily acted on compounds containing glucose units. Bf2006 significantly affected the content of lignin, neutral detergent fiber, acid detergent fiber, and the microstructure of wheat straw, with degradation products primarily consisting of disaccharides, oligosaccharides, polysaccharides, glycosides, and other carbohydrates. This study provides theoretical guidance for the production and application of mixed cellulase Bf2006, serving as a reference for the industrial use of different cellulase types.

The Effects of Carbon Source and Growth Temperature on the Fatty Acid Profiles of Thermobifida fusca

The aerobic, thermophilic Actinobacterium, Thermobifida fusca has been proposed as an organism to be used for the efficient conversion of plant biomass to fatty acid-derived precursors of biofuels or biorenewable chemicals. Despite the potential of T. fusca to catabolize plant biomass, there is remarkably little data available concerning the natural ability of this organism to produce fatty acids. Therefore, we determined the fatty acids that T. fusca produces when it is grown on different carbon sources (i.e., glucose, cellobiose, cellulose and avicel) and at two different growth temperatures, namely at the optimal growth temperature of 50°C and at a suboptimal temperature of 37°C. These analyses establish that T. fusca produces a combination of linear and branched chain fatty acids (BCFAs), including iso-, anteiso-, and 10-methyl BCFAs that range between 14- and 18-carbons in length. Although different carbon sources and growth temperatures both quantitatively and qualitatively affect the fatty acid profiles produced by T. fusca, growth temperature is the greater modifier of these traits. Additionally, genome scanning enabled the identification of many of the fatty acid biosynthetic genes encoded by T. fusca.

Recombinant cellobiohydrolase of Myceliophthora thermophila: characterization and applicability in cellulose saccharification

A codon optimized cellobiohydrolase (CBH) encoding synthetic gene of 1188 bp from a thermophilic mold Myceliophthora thermophila (MtCel6A) was cloned and heterologously expressed in Escherichia coli for the first time. In silico analysis suggested that MtCel6A is a GH6 CBH and belongs to CBHII family, which is structurally similar to Cel6A of Humicola insolens. The recombinant MtCel6A is expressed as active inclusion bodies, and the molecular mass of the purified enzyme is ~ 45 kDa. The rMtCel6A is active in a wide range of pH (4-12) and temperatures (40-100 °C) with optima at pH 10.0 and 60 °C. It exhibits T1/2 of 6.0 and 1.0 h at 60 and 90 °C, respectively. The rMtCel6A is an extremozyme with organic solvent, salt and alkali tolerance. The Km, Vmax, kcat and kcat/Km values of the enzyme are 3.2 mg mL-1, 222.2 μmol mg-1 min-1, 2492 s-1 and 778.7 s-1 mg-1 mL-1, respectively. The product analysis of rMtCel6A confirmed that it is an exoenzyme that acts from the non-reducing end of cellulose. The addition of rMtCel6A to the commercial cellulase mix (Cellic CTec2) led to 1.9-fold increase in saccharification of the pre-treated sugarcane bagasse. The rMtCel6A is a potential CBH that finds utility in industrial processes such as in bioethanol, paper pulp and textile industries.

Enhanced Thermostability and Enzymatic Activity of Cel6A Variants from Thermobifida fusca by Empirical Domain Engineering (Short Title: Domain Engineering of Cel6A)

Cellulases are a set of lignocellulolytic enzymes, capable of producing eco-friendly low-cost renewable bioethanol. However, low stability and hydrolytic activity limit their wide-scale applicability at the industrial scale. In this work, we report the domain engineering of endoglucanase (Cel6A) of Thermobifida fusca to improve their catalytic activity and thermal stability. Later, enzymatic activity and thermostability of the most efficient variant named as Cel6A.CBC was analyzed by molecular dynamics simulations. This variant demonstrated profound activity against soluble and insoluble cellulosic substrates like filter paper, alkali-treated bagasse, regenerated amorphous cellulose (RAC), and bacterial microcrystalline cellulose. The variant Cel6A.CBC showed the highest catalysis of carboxymethyl cellulose (CMC) and other related insoluble substrates at a pH of 6.0 and a temperature of 60 °C. Furthermore, a sound rationale was observed between experimental findings and molecular modeling of Cel6A.CBC which revealed thermostability of Cel6A.CBC at 26.85, 60.85, and 74.85 °C as well as structural flexibility at 126.85 °C. Therefore, a thermostable derivative of Cel6A engineered in the present work has enhanced biological performance and can be a useful construct for the mass production of bioethanol from plant biomass.