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Appl. Environ. Microbiol., Feb 1995, 518-525, Vol 61, No. 2
CD Skory and SN Freer
The ability of yeasts to ferment cellodextrins is rare. Candida wickerhamii
is able to use these sugars for alcohol production because of a cell-bound,
extracellular, beta-glucosidase that is unusual by not being inhibited by
glucose. A cDNA expression library in lambda phage was prepared with mRNA
isolated from cellobiose-grown C. wickerhamii. Immunological screening of
the library with polyclonal antibodies against purified C. wickerhamii
cell-bound, extracellular beta- glucosidase yielded 12 positive clones.
Restriction endonuclease analysis and sequence data revealed that the
clones could be divided into two groups, bglA and bglB, which were shown to
be genetically distinct by Southern hybridization analyses. Efforts were
directed at the study of bglB since it appeared to code for the cell-bound
beta- glucosidase. Sequence data from both cDNA and genomic clones showed
the absence of introns in bglB. Sodium dodecyl sulfate-polyacrylamide gel
electrophoresis and immunoblotting of cell lysates from Escherichia coli
bglB clones confirmed the presence of an expressed protein with an apparent
molecular mass of 72 kDa, which is consistent with that expected for an
unglycosylated form of the enzyme. Amino acid comparisons of BglB with
other beta-glucosidase sequences suggest that it is a member of family 1
glycosyl hydrolases but is unusual in that it contains an additional 100 to
130 amino acids at the N terminus. This sequence did not have homologies to
other known protein sequences and may impart unique properties to this
beta-glucosidase.
Cloning and characterization of a gene encoding a cell-bound, extracellular beta-glucosidase in the yeast Candida wickerhamii
Fermentation Biochemistry Research Unit, USDA Agricultural Research Service, Peoria, Illinois 61604, USA.
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