Abstract:
BACKGROUND: β-Fructofuranosidases (or invertases) catalyse the commercially-important biotransformation of
sucrose into short-chain fructooligosaccharides with wide-scale application as a prebiotic in the functional foods
and pharmaceutical industries.
RESULTS: We identified a β-fructofuranosidase gene (CmINV) from a Ceratocystis moniliformis genome sequence
using protein homology and phylogenetic analysis. The predicted 615 amino acid protein, CmINV, grouped with an
existing clade within the glycoside hydrolase (GH) family 32 and showed typical conserved motifs of this enzyme
family. Heterologous expression of the CmINV gene in Saccharomyces cerevisiae BY4742Δsuc2 provided further
evidence that CmINV indeed functions as a β-fructofuranosidase. Firstly, expression of the CmINV gene complemented
the inability of the Δsuc2 deletion mutant strain of S. cerevisiae to grow on sucrose as sole carbohydrate source.
Secondly, the recombinant protein was capable of producing short-chain fructooligosaccharides (scFOS) when
incubated in the presence of 10% sucrose. Purified deglycosylated CmINV protein showed a molecular weight of ca.
66 kDa and a Km and Vmax on sucrose of 7.50 mM and 986 μmol/min/mg protein, respectively. Its optimal pH and
temperature conditions were determined to be 6.0 and 62.5°C, respectively. The addition of 50 mM LiCl led to a 186%
increase in CmINV activity. Another striking feature was the relatively high volumetric production of this protein in
S. cerevisiae as one mL of supernatant was calculated to contain 197 ± 6 International Units of enzyme.
CONCLUSION: The properties of the CmINV enzyme make it an attractive alternative to other invertases being used
in industry.
