Isolation and some properties of two extracellular β-glucosidases from Trichosporon adeninovorans

Expression and characterization of Pichia etchellsii beta-glucosidase in Escherichia coli

The beta-glucosidase enzyme is important as the terminal enzyme involved in hydrolysis of cellobiose and short-chain cellodextrins generated during enzymatic cellulose degradation. Under controlled reaction conditions the enzyme also displays cello-oligosaccharide synthesizing ability (based on either the thermodynamic or kinetic approach). We present here the purification of the enzyme beta-glucosidase (BGL) of Pichia etchellsii from recombinant pBG55 Escherichia coli clone. The kinetic parameters, substrate specificity and oligosaccharide synthesizing ability of the purified enzyme are also reported. The purified 200-kDa protein (tetramer of 50 kDa) was identified as a broad-substrate-specificity enzyme exhibiting increased temperature and glucose tolerance compared to the native yeast enzyme. Temperature directed substrate specificity for aryl beta,1-4 linkage, and beta (1-2), beta(1-4), beta(1-6) and beta(2-1) linkages in various natural disaccharides was observed. Glycosylation of the enzyme was found to be unimportant for enzyme activity. With both cellobiose and glucose, oligosaccharide synthesis was detected. The implications of this information with regard to cellulose hydrolysis and oligosaccharide synthesis are discussed.

Temperature-dependent dimorphism of the yeast Arxula adeninivorans Ls3

Arxula adeninivorans Ls3 is described as an ascomycetous, arthroconidial, anamorphic, xerotolerant yeast, which was selected from wood hydrolysates in Siberia. By using minimal salt medium or yeast-extract-peptone-medium with glucose or maltose as carbon source it was shown that this yeast is able to grow at up to 48 degrees C. Increasing temperatures induce changes in morphology from the yeast phase to mycelia depending on an altered programme of gene expression. This dimorphism is an environmentally conditioned (reversible) event and the mycelia can be induced at a cultivation temperature of 45 degrees C. Depending on the morphology of strain Ls3 (yeast phase or mycelia) the secretion behaviour as well as the spectrum of polypeptides accumulated in the culture medium changed. The activities of the accumulated extracellular enzymes glucoamylase and invertase were 2 to 3 times higher in cultures grown at 45 degrees C than in those grown at 30 degrees C. While the level of the glucoamylase protein secreted from mycelia between 45 and 70 hours did not change, biochemical activity decreased after a cultivation time of 43 hours. It was shown that this effect depended on both the catabolic repression of the glucoamylase by glucose and the thermal inactivation of this enzyme in media without or with low concentrations of starch or maltose.

Characterization of Arxula adeninivorans strains from different habitats

Some Arxula adeninivorans strains selected from wood hydrolysates in Siberia, from soil in South Africa and from maize silage and soil in The Netherlands were compared. DNA-fingerprinting, pulse field gel electrophoresis as well as analysis of secretory proteins have been chosen to describe the similarities among the strains. Combination of the three methods allowed identification of each strain. Strains from the same origin show extensive similarities. The results of the DNA-fingerprints indicate that the strain isolated in Siberia belongs to the group of strains originated from South Africa. However, it differed in the molecular weight of the third chromosome and in the pattern of secretory proteins from the South African isolates.

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).