Optimizing the biocatalytic productivity of an engineered sialidase from Trypanosoma rangeli for 3'-sialyllactose production.

An engineered sialidase, Tr6, from Trypanosoma rangeli was used for biosynthetic production of 3'-sialyllactose, a human milk oligosaccharide case compound, from casein glycomacropeptide (CGMP) and lactose, components abundantly present in industrial dairy side streams. Four different enzyme re-use methods were compared to optimize the biocatalytic productivity, i.e. 3'-sialyllactose formation per amount of Tr6 employed: (i) His-tag immobilization on magnetic Cu²âº-iminodiacetic acid-functionalized nanoparticles (MNPs), (ii) membrane immobilization, (iii) calcium alginate encapsulation of cross-linked Tr6, and (iv) Tr6 catalysis in a membrane reactor. Tr6 immobilized on MNPs gave a biocatalytic productivity of 84 mg 3'-sialyllactose/mg Tr6 after seven consecutive reaction runs. Calcium-alginate and membrane immobilization were inefficient. Using free Tr6 in a 10 kDa membrane reactor produced a 9-fold biocatalytic productivity increase compared to using free Tr6 in a batch reactor giving 306 mg 3'-sialyllactose/mg Tr6 after seven consecutive reaction runs. The 3'-sialyllactose yield on α-2,3-bound sialic acid in CGMP was 74%. Using circular dichroism, a temperature denaturation midpoint of Tr6, Tm, of 57.2 °C was determined. The thermal stability of free Tr6 was similarly high and the Tr6 was stable at the reaction temperature (25 °C) for at least 24 h.