Characterization of extracellular acid phosphatases from the yeast Arxula adeninivorans

Acid phosphatase production by recombinant Arxula adeninivorans

Acid phosphatase production by recombinant Arxula adeninivorans was carried out in submerged fermentation. Using the Plackett-Burman design, three fermentation variables (pH, sucrose concentration, and peptone concentration) were identified to significantly affect acid phosphatase and biomass production, and these were optimized using response surface methodology of central composite design. The highest enzyme yields were attained in the medium with 3.9% sucrose and 1.6% peptone at pH 3.8. Because of optimization, 3.86- and 4.19-fold enhancement in enzyme production was achieved in shake flasks (17,054 U g(-1) DYB) and laboratory fermenter (18,465 U g(-1) DYB), respectively.

Application of a wide-range yeast vector (CoMed) system to recombinant protein production in dimorphic Arxula adeninivorans, methylotrophic Hansenula polymorpha and other yeasts

BACKGROUND

Yeasts provide attractive expression platforms in combining ease of genetic manipulation and fermentation of a microbial organism with the capability to secrete and to modify proteins according to a general eukaryotic scheme. However, early restriction to a single yeast platform can result in costly and time-consuming failures. It is therefore advisable to assess several selected systems in parallel for the capability to produce a particular protein in desired amounts and quality. A suitable vector must contain a targeting sequence, a promoter element and a selection marker that function in all selected organisms. These criteria are fulfilled by a wide-range integrative yeast expression vector (CoMed) system based on A. adeninivorans- and H. polymorpha-derived elements that can be introduced in a modular way.

RESULTS

The vector system and a selection of modular elements for vector design are presented. Individual single vector constructs were used to transform a range of yeast species. Various successful examples are described. A vector with a combination of an rDNA sequence for genomic targeting, the E. coli-derived hph gene for selection and the A. adeninivorans-derived TEF1 promoter for expression control of a GFP (green fluorescent protein) gene was employed in a first example to transform eight different species including Hansenula polymorpha, Arxula adeninivorans and others. In a second example, a vector for the secretion of IL-6 was constructed, now using an A. adeninivorans-derived LEU2 gene for selection of recombinants in a range of auxotrophic hosts. In this example, differences in precursor processing were observed: only in A. adeninivorans processing of a MFalpha1/IL-6 fusion was performed in a faithful way.

CONCLUSION

rDNA targeting provides a tool to co-integrate up to 3 different expression plasmids by a single transformation step. Thus, a versatile system is at hand that allows a comparative assessment of newly introduced metabolic pathways in several organisms or a comparative co-expression of bottleneck genes in cases where production or secretion of a certain product is impaired.

A novel estrogen sensor based on recombinant Arxula adeninivorans cells

A novel yeast cell-based assay was developed for the detection of estrogenic activity in wastewater. Recombinant Arxula adeninivorans strains were engineered to co-express the human estrogen receptor alpha (hERalpha) and a Klebsiella-derived phytase (phyK) reporter gene under the control of an A. adeninivorans-derived glucoamylase (GAA) promoter which had been modified by the insertion of estrogen-responsive elements (EREs). In the presence of estrogenic compounds, hERalpha dimerizes and binds to the estrogen. Reporter gene expression is induced by subsequent binding of the hERalpha-dimer/estrogen complex to estrogen responsive elements (ERE) in the promoter. The insertion of different numbers of EREs in three alternative promoter positions and its effect on reporter gene expression were assessed. In one of the constructs, a detection limit of 5 ng l(-1) and a determination limit of 10 ng l(-1) for 17beta-estradiol-like activity was achieved. The photometric assay used enabled estrogen determination in sewage samples within 30 h.

Comparative biochemical, genetical and immunological studies of glucoamylase producing Arxula adeninivorans yeast strains

Seven Arxula adeninivorans strains originating from The Netherlands (CSIR 1136, CSIR 1138 and CBS 8244T), South Africa (CSIR 1147, CSIR 1148 and CSIR 1149) and Siberia (Ls3) were compared concerning their secretory glucoamylase. Within the spectrum of secretory polypeptides obtained by SDS-polyacrylamide gel electrophoresis, the glucoamylase corresponding polypeptide, could be identified by means of specific antibodies directed against the glucoamylase of strain Ls3. The molecular masses of the glucoamylases vary from 84 to 95 kDa. After endoglycosidase F treatment of the secretory proteins, the N-linked carbohydrate content for each glucoamylase could be quantified at about 25%. Glucoamylase activity staining of secretory proteins separated under nondenaturing conditions revealed one glucoamylase active protein for the Dutch strains and two active forms for the strains originating from South Africa and Siberia. Highest activities of glucoamylase can be measured at the end of the exponential growth phase for each strain. The Dutch strain CSIR 1138 secretes the highest activity. Optimum values for temperature and pH were determined and compared. By means of pulsed field gel electrophoresis and Southern analysis, the glucoamylase corresponding gene could be localized on the second of the four chromosomes of each yeast strain.

Comparison of the phosphate-repressible and-constitutive acid phosphatases of Yarrowia lipolytica

The phosphate-repressible acid phosphatase from Yarrowia lipolytica cells was more thermostable but more sensitive to urea denaturation and to the effect of Triton X-100 than the constitutive counterpart. The K m values of the repressible and constitutive enzymes for p-nitrophenyl phosphate were 3.6 mM and 7.4 mM, respectively. They are judged to be distinct proteins.

Purification and characterization of beta-xylosidase activities from the yeast Arxula adeninivorans

beta-Xylosidase activity has been detected in cell-free extracts, in culture fluids and as cell wall-bound enzyme of Arxula adeninivorans. With chromatographic procedures used to purify the activity two different forms of beta-xylosidase (denoted beta X-1 and beta X-2) from the cell-free extract and from the culture medium could be separated, but only one form (beta X-2) was present in the cell wall. Both forms are glycoproteins and were deglycosylated by endoglycosidase H treatment. The molecular masses of the enzymes under native and denaturing conditions suggest that beta X-2 is the dimer of beta X-1. M(r) of the native beta X-1 was 60 kDa and after deglycosylation 39 kDa determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Some enzymatic properties of beta X-1 and beta X-2 and of their deglycosylated products were studied and showed, with one exception, wide similarities. The maximum activity was reached at pH 5.0 and 60 degrees C. The enzymes hydrolyze only beta-glycosidic bound beta-xylopyranosides and the Km values for p-nitrophenyl-beta-xylopyranoside were determined to be 0.23-0.33 mM. The beta-xylosidase activity was inhibited competitively by xylose. The deglycosylated enzymes were, however, stronger inhibited (Ki = 2.1 mM) as their glycosylated ones (Ki = 5.8 mM).