β-Galactosidase from Kluyveromyces lactis: Characterization, production, immobilization and applications - A review

A review on the enzyme β-galactosidase from Kluyveromyces lactis is presented, from the perspective of its structure and mechanisms of action, the main catalyzed reactions, the key factors influencing its activity, and selectivity, as well as the main techniques used for improving the biocatalyst functionality. Particular attention was given to the discussion of hydrolysis, transglycosylation, and galactosylation reactions, which are commonly mediated by this enzyme. In addition, the products generated from these processes were highlighted. Finally, biocatalyst improvement techniques are also discussed, such as enzyme immobilization and protein engineering. On these topics, the most recent immobilization strategies are presented, emphasizing processes that not only allow the recovery of the biocatalyst but also deliver enzymes that show better resistance to high temperatures, chemicals, and inhibitors. In addition, genetic engineering techniques to improve the catalytic properties of the β-galactosidases were reported. This review gathers information to allow the development of biocatalysts based on the β-galactosidase enzyme from K. lactis, aiming to improve existing bioprocesses or develop new ones.

Preparation of CLEAs and magnetic CLEAs of a recombinant l-arabinose isomerase for d-tagatose synthesis

The insolubilization of a recombinant l-arabinose isomerase (l-AI) from Enterococcus faecium by cross-linked enzyme aggregates (CLEA) was investigated, aiming the biochemical production of d-tagatose from d-galactose. d-tagatose is a functional sweetener that has many health benefits, sweetening properties and lower calorific value. Different precipitants (ammonium sulfate, ethanol, acetone, polyethylene glycol 4000) were used in the first step of the protocol, in order to establish the precipitation conditions, and the best results of yield and activity were achieved with ammonium sulfate. In order to facilitate the recovery of the biocatalyst, a new strategy for immobilization of the multimeric enzyme l-arabinose isomerase was proposed. Magnetic cross-linked enzyme aggregates (m-CLEA) were obtained using ammonium sulfate as precipitant and magnetic nanoparticles (MNP) functionalized with APTES (3- Aminopropyltriethoxysilane). Another immobilization strategy was to immobilize the enzyme onto MNP-APTES, as a control. The best results were achieved when the m-CLEA was produced with 20 mg of MNP, 7.69 U. g^-1 of enzymatic activity, 7.61 % of recovered activity, 99 % of yield of immobilization. On the other hand, the enzyme immobilized onto MNP-APTES, presented only 2.12 U. g^-1 of enzymatic activity, 32.3 % of recovered activity, and 15 % of yield of immobilization.

One-Step Immobilization and Stabilization of a Recombinant Enterococcus faecium DBFIQ E36 L-Arabinose Isomerase for D-Tagatose Synthesis

A recombinant L-arabinose isomerase from Enterococcus faecium DBFIQ E36 was immobilized onto multifunctional epoxide supports by chemical adsorption and onto a chelate-activated support via polyhistidine-tag, located on the N-terminal (N-His-L-AI) or on the C-terminal (C-His-L-AI) sequence, followed by covalent bonding between the enzyme and the support. The results were compared to reversible L-AI immobilization by adsorption onto charged agarose supports with improved stability. All the derivatives presented immobilization yields of above 75%. The ionic interaction established between agarose gels containing monoaminoethyl-N-aminoethyl structures (MANAE) and the enzyme was the most suitable strategy for L-AI immobilization in comparison to the chelate-activated agarose. In addition, the immobilized biocatalysts by ionic interaction in MANAE showed to be the most stable, retaining up to 100% of enzyme activity for 60 min at 60 °C and with K_m values of 28 and 218 mM for MANAE-N-His-L-AI and MANAE-C-His-L-AI, respectively.

Engineering the l-Arabinose Isomerase from Enterococcus Faecium for d-Tagatose Synthesis

l-Arabinose isomerase (EC 5.3.1.4) (l-AI) from Enterococcus faecium DBFIQ E36 was overproduced in Escherichia coli by designing a codon-optimized synthetic araA gene. Using this optimized gene, two N- and C-terminal His-tagged-l-AI proteins were produced. The cloning of the two chimeric genes into regulated expression vectors resulted in the production of high amounts of recombinant N-His-l-AI and C-His-l-AI in soluble and active forms. Both His-tagged enzymes were purified in a single step through metal-affinity chromatography and showed different kinetic and structural characteristics. Analytical ultracentrifugation revealed that C-His-l-AI was preferentially hexameric in solution, whereas N-His-l-AI was mainly monomeric. The specific activity of the N-His-l-AI at acidic pH was higher than that of C-His-l-AI and showed a maximum bioconversion yield of 26% at 50 °C for d-tagatose biosynthesis, with Km and Vmax parameters of 252 mM and 0.092 U mg^-1, respectively. However, C-His-l-AI was more active and stable at alkaline pH than N-His-l-AI. N-His-l-AI follows a Michaelis-Menten kinetic, whereas C-His-l-AI fitted to a sigmoidal saturation curve.

Ecotaxis: the principle and its application to the study of Hodgkin's disease

A study of the function, characterization and distribution of T and B lymphocytes in five children with Hodgkin's disease is presented. The results, indicating that lymphocyte depletion in the peripheral blood does not necessarily reflect an overall lack of circulating lymphocytes, are presented to demonstrate that failure of ecotaxis (normal lymphocyte migration and distribution) can occur in man. The underlying reasons for such failure and their relevance to the pathogenesis of Hodgkin's disease are discussed.

Chronic mucocutaneous candidiasis treated with transfer factor

A patient with chronic mucocutaneous candidiasis resistant to all tropical therapy has had extensive tests of immunological function carried out before and after administration of transfer factor. Immunological testing has been both specific, directed at responses to candida antigen, and non-specific, directed at general assessment of the patient's immune status. Transfer factor has been administered on three occasions in the past year. After each treatment temporary clinical improvement accompanied by changes in both specific and non-specific immunological responses have been observed. The possible mode of action of transfer factor in this case is discussed.