Development of a large scale process for the conversion of polysialogangliosides to monosialotetrahexosylganglioside with a novel strain of Brevibacterium casei producing sialidase

Preparation of Ganglioside GM1 by Supercritical CO2 Extraction and Immobilized Sialidase

Monosialotetrahexosylganglioside (GM1) has good activity on brain diseases and was developed to be a drug applied in clinics for neurological disorders and nerve injury. It is difficult to isolate GM1 in industry scale from the brains directly. In this work, a simple and highly efficient method with high yield was developed for the isolation, conversion, and purification of GM1 from a pig brain. Gangliosides (GLS) were first extracted by supercritical CO₂ (SCE). The optimum extraction time of GLS by SCE was 4 h, and the ratio of entrainer to acetone powder from the pig brain was 3:1 (v/w). GM1 was then prepared from GLS by immobilized sialidase and purified by reverse-phase silica gel. Sodium alginate embedding was used for the immobilization of sialidase. Under the optimized method, the yield of high-purity GM1 was around 0.056%. This method has the potential to be applied in the production of GM1 in the industry.

Cloning, expression, and characterization of a novel sialidase from Brevibacterium casei

The sialidase gene from Brevibacterium casei was cloned in pET28a and overexpressed as a histidine-tagged protein in Escherichia coli BL21(DE3). The histidine-tagged sialidase protein was purified and characterized from the crude cell extracts of isopropyl-β-d-thiogalactopyranoside-induced cells using Ni-NTA agarose chromatography. SDS-PAGE using the purified sialidase indicated a single band at 116 kDa. This sialidase showed maximum activity at a pH of 5.5 and temperature of 37 °C. The kinetic parameters K_m and V_max for the artificial substrate 2'-(4-methylumbelliferyl)-α-d-N-acetyl-neuraminic acid sodium salt hydrate were 1.69 × 10^-3 mM and 244 mmol·Min^-1 ·mg^-1 , respectively. The sialidase may catalyze the hydrolysis of terminal sialic acids linked by the α-(2,3) and α-(2,8) linkage of polysialogangliosides, but it does not act on monosialotetrahexosylganglioside (GM1), which offers it a great potential for commercially producing GM1 from polysialogangliosides.

Efficient biotransformation of polysialogangliosides for preparation of GM1 by Cellulosimicrobium sp. 21

A new ganglioside transformed strain isolated from soil was identified as Cellulosimicrobium sp. 21. It produced a sialidase which transformed polysialo-gangliosides GD1 and GT1 into a monosialoterahexosylganglioside, i.e., ganglioside GM1. The sialidase had both NeuAc-α-2,3- and NeuAc-α-2,8-sialidase activity without producing asiolo-GM1. The optimum conditions were evaluated and it was found that the transformation was optimally performed at 30 °C and pH 7.0. The substrate should be added at the beginning of the reaction and the concentration of substrate was 3% (w/v). Under these optimum conditions, Cellulosimicrobium sp. 21 converted GD1 and GT1 into GM1 in inorganic medium in a 5 L bioreactor with the recovery rate of 69.3%. The product contained 50.3% GM1 and was purified on silica to give the product with 95% of GM1 with a recovery rate of 30.5%. Therefore, Cellulosimicrobium sp. 21 has potential to be applied in the production of GM1 in the pharmaceutical industry.

Development of a cell immobilization technique for the conversion of polysialogangliosides to monosialotetrahexosylganglioside

CONTEXT

Monosialotetrahexosylganglioside (GM₁) prepared from the brain of pig or bovine is an effective clinical drug in the treatment of different nervous system diseases. Generally, polysialogangliosides are transformed into GM₁ by enzymic or chemical hydrolysis due to the very poor level of natural GM₁.

OBJECTIVE

To continuously obtain GM₁ by cell immobilization in a packed-bed reactor.

MATERIALS AND METHODS

Brevibacterium casei, which is Gram-positive bacteria belonging to the order Actinomyces and family Brevibacteriaceae, can produce high-activity sialidase, are encapsulated in silk fibroin hydrogel, and subsequently packed into a reactor. The crude ganglioside is pumped into the reactor and continuously turned to GM₁.

RESULTS

The optimal silk fibroin concentration for hydrogel preparation is 6.0% (w/v). The optimal initial biomass for immobilization is ~12% (wet weight). The optimal conversion conditions are 35 °C and 6  mL/min of flow rate. Under above conditions, the maximum GM₁ productive strength and conversion ratio can reach to 4.2 g/L·h and 313.5%, respectively.

DISCUSSION

Silk fibroin is a promising material for cell immobilization because it has predominant characteristics of higher permeability and intensity. Cell immobilization for continuous GM₁ transformation could eliminate the asialo GM₁ and decrease the foreign matter from transfer medium and metabolism product.

CONCLUSION

In the packed-bed reactor, continuous production of GM₁ had been under effective running at least for 15 days indicating a potential for industrial production. It is significant that this is a first report on cell immobilization for GM₁ production.

Efficient conversion from polysialogangliosides to monosialotetrahexosylganglioside using Oerskovia xanthineolytica YZ-2

A new sialidase-producing strain isolated from soil was identified as Oerskovia xanthineolytica YZ-2. Sialidase was produced when Oerskovia xanthineolytica YZ-2 was exposed to polysialogangliosides. The sialidase of Oerskovia xanthineolytica YZ-2 hydrolyzed sialic acid linkages in polysialogangliosides, and released monosialotetrahexosylganglioside (GM1). The sialidase had the capability of product specificity because it did not attack the sialic acid linkage in GM1. Therefore, Oerskovia xanthineolytica YZ-2 was used for GM1 production from polysialogangliosides. In flasks cultivation phase, it was proved that Oerskovia xanthineolytica YZ-2 could convert polysialogangliosides to GM1 efficiently. Scaling-up the bioprocess with 8% crude ganglioside, polysialogangliosides was converted to GM1 by Oerskovia xanthineolytica YZ-2 in 30 L bioreactor after 18 h. The relative content of GM1 increased from 16.3% in crude ganglioside to 83.7% after Oerskovia xanthineolytica YZ-2 conversion. Therefore, a simple, large-scale conversion process for GM1 production from polysialogangliosides was achieved using Oerskovia xanthineolytica YZ-2 as a biocatalyst.