Effect of Vitreoscilla Hemoglobin and Culture Conditions on Production of Bacterial l-Asparaginase, an Oncolytic Enzyme

L-Asparaginase from Penicillium sizovae Produced by a Recombinant Komagataella phaffii Strain

L-asparaginase is an important enzyme in the pharmaceutical field used as treatment for acute lymphoblastic leukemia due to its ability to hydrolyze L-asparagine, an essential amino acid synthesized by normal cells, but not by neoplastic cells. Adverse effects of L-asparaginase formulations are associated with its glutaminase activity and bacterial origin; therefore, it is important to find new sources of L-asparaginase produced by eukaryotic microorganisms with low glutaminase activity. This work aimed to identify the L-asparaginase gene sequence from Penicillium sizovae, a filamentous fungus isolated from the Brazilian Savanna (Cerrado) soil with low glutaminase activity, and to biosynthesize higher yields of this enzyme in the yeast Komagataella phaffii. The L-asparaginase gene sequence of P. sizovae was identified by homology to L-asparaginases from species of Penicillium of the section Citrina: P. citrinum and P. steckii. Partial L-asparaginase from P. sizovae, lacking the periplasmic signaling sequence, was cloned, and expressed intracellularly with highest enzymatic activity achieved by a MUT⁺ clone cultured in BMM expression medium; a value 5-fold greater than that obtained by native L-asparaginase in P. sizovae cells. To the best of our knowledge, this is the first literature report of the heterologous production of an L-asparaginase from a filamentous fungus by a yeast.

l-asparaginase production and enhancement by Sarocladium strictum: In vitro evaluation of anti-cancerous properties

AIMS

Utilization of l-asparaginase has been one of the effective strategies for the treatment of lymphoblastic leukaemia. Since the currently used bacterial l-asparaginase causes side effects, searching for new enzyme sources has been an active field of research. This study focuses on the characterization of an l-asparaginase-producing fungal strain.

METHODS AND RESULTS

Sarocladium strictum was identified as a potent enzyme-producing strain. For the enhancement of enzyme production, we used two-level factorial design and response surface methodology. The optimization of significant factors showed a 1·84-fold increase in enzyme production. The K_m and V_max values of the enzyme were 9·74 mmol l^-1 and 8·19 μmol min^-1 . The toxicity of the produced l-asparaginase was measured on K562 and HL60 cancer cell lines and L6 as normal cells. The IC₅₀ values were calculated as 0·4 and 0·5 IU ml^-1 for K562 and HL60 respectively and no significant effect was observed in L6. BrdU proliferation and caspase-3 activity assay in l-asparaginase treated HL60 and K562 cells indicated that cell proliferation rates and apoptotic cell death were reduced.

CONCLUSIONS

The cytotoxic properties of the produced fungal enzyme indicated significant growth inhibition in cancer cells while having a little toxic effect on normal cells. The possibility of mass production alongside having suitable cytotoxic and kinetic properties suggest the probable use of the produced l-asparaginase for further researches as a potential chemotherapeutic agent.

SIGNIFICANCE AND IMPACT OF THE STUDY

The lack of significant l-glutaminase activity and promising toxicity properties in S. strictum and the closer evolutionary relativeness of fungi enzymes to human enzymes compared to bacterial enzymes suggest a new source with lower toxicity and anti-cancerous properties, causing less side effect problems.

Recent applications of Vitreoscilla hemoglobin technology in bioproduct synthesis and bioremediation

Since its first use in 1990 to enhance production of α-amylase in E. coli, engineering of heterologous hosts to express the hemoglobin from the bacterium Vitreoscilla (VHb) has become a widely used strategy to enhance production of a variety of bioproducts, stimulate bioremediation, and increase growth and survival of engineered organisms. The hosts have included a variety of bacteria, yeast, fungi, higher plants, and even animals. The beneficial effects of VHb expression are presumably the result of one or more of its activities. The available evidence indicates that these include oxygen binding and delivery to the respiratory chain and oxygenases, protection against reactive oxygen species, and control of gene expression. In the past 4 to 5 years, the use of this "VHb technology" has continued in a variety of biotechnological applications in a wide range of organisms. These include enhancement of production of an ever wider array of bioproducts, new applications in bioremediation, a possible role in enhancing aerobic waste water treatment, and the potential to enhance growth and survival of both plants and animals of economic importance.