Microbial glucoamylases: structural and functional properties and biotechnological uses.

Glucoamylases (GAs) are one of the principal groups of enzymes involved in starch hydrolysis and belong to the glycosylhydrolase family. They are classified as exo-amylases due to their ability to hydrolyze α-1,4 glycosidic bonds from the non-reducing end of starch, maltooligosaccharides, and related substrates, releasing ß-D-glucose. Structurally, GAs possess a characteristic catalytic domain (CD) with an (α/α)6 fold and exhibit five conserved regions within this domain. The CD may or may not be linked to a non-catalytic domain with variable functions depending on its origin. GAs are versatile enzymes with diverse applications in food, biofuel, bioplastic and other chemical industries. Although fungal GAs are commonly employed for these purposes, they have limitations such as their low thermostability and an acidic pH requirement. Alternatively, GAs derived from prokaryotic organisms are a good option to save costs as they exhibit greater thermostability compared to fungal GAs. Moreover, a group of cold-adapted GAs from psychrophilic organisms demonstrates intriguing properties that make them suitable for application in various industries. This review provides a comprehensive overview of the structural and sequential properties as well as biotechnological applications of GAs in different industrial processes.

Identification, molecular and biochemical characterization of a novel thermoactive and thermostable glucoamylase from Thermoanaerobacter ethanolicus.

PURPOSE: We identified a new glucoamylase (TeGA) from Thermoanaerobacter ethanolicus, a thermophilic anaerobic bacterium. Structural studies suggest that TeGA belongs to the family 15 of glycosylhydrolases (GH15). METHODS: The expression of this enzyme was optimized in E. coli (BL21) cells in order to have the highest amount of soluble protein (around 3 mg/l of culture medium). RESULTS: TeGA showed a high optimum temperature of 75 °C. It also showed one of the highest specific activities reported for a bacterial glucoamylase (75.3 U/mg) and was also stable in a wide pH range (3.0-10.0). Although the enzyme was preferentially active with maltose, it was also able to hydrolyze different soluble starches such as those from potato, corn or rice. TeGA showed a high thermostability up to around 70 °C, which was increased in the presence of PEG8000, and also showed to be stable in the presence of moderate concentrations of ethanol. CONCLUSION: We propose that TeGA could be suitable for use in different industrial processes such as biofuel production and food processing.

Characterization of SdGA, a cold-adapted glucoamylase from Saccharophagus degradans.

We investigated the structural and functional properties of SdGA, a glucoamylase (GA) from Saccharophagus degradans, a marine bacterium which degrades different complex polysaccharides at high rate. SdGA is composed mainly by a N-terminal GH15_N domain linked to a C-terminal catalytic domain (CD) found in the GH15 family of glycosylhydrolases with an overall structure similar to other bacterial GAs. The protein was expressed in Escherichia coli cells, purified and its biochemical properties were investigated. Although SdGA has a maximum activity at 39 °C and pH 6.0, it also shows high activity in a wide range, from low to mild temperatures, like cold-adapted enzymes. Furthermore, SdGA has a higher content of flexible residues and a larger CD due to various amino acid insertions compared to other thermostable GAs. We propose that this novel SdGA, is a cold-adapted enzyme that might be suitable for use in different industrial processes that require enzymes which act at low or medium temperatures.

A combined experimental and molecular simulation study of factors influencing interaction of quinoa proteins-carrageenan.

The interaction between quinoa proteins isolate (QP isolate) and the negatively charged polysaccharide ι-Carragennan (Carr) as a function of pH was studied. Experimental measurements as turbidity, hydrophobic surface, ζ-potential, and hydrodynamic size were carried out. Associative interaction between QP and Carr was found in the pH range between 1 and 2.9. When both molecules are negatively charged (pH>5,5), a pure Coulombic repulsion regime is observed and the self-association of QP due to the Carr exclusion is proposed. In the intermediate pH range, the experimental data suggests that the charge regulation mechanism can overcome the electrostatic repulsion that may take place (and an attraction between QP and Carr can still be observed). Computational simulations by means of free energy derivatives using the Monte Carlo method were carried out to better understand the interaction mechanism between QP and Carr. QP was modeled as a single protein using one of the major proteins, Chenopodin (Ch), and Carr was modeled as a negatively charged polyelectrolyte (NCP) chain, both in the cell model framework. Simulation results showed attractive interactions in agreement with the experimental data.