Schwanniomyces occidentalis invertase is an extracellular
enzyme that hydrolizes sucrose and releases -fructose from
various oligosaccharides and essential storage fructan polymers
such as inulin. We report here the three-dimensional structure
of Sw. occidentalis invertase at 2.9A˚ resolution and its complex
with fructose at 1.9 A˚ resolution. The monomer presents a
bimodular arrangement common to other GH32 enzymes, with
an N-terminal 5-fold -propeller catalytic domain and a C-terminal
-sandwich domain for which the function has been
unknown until now. However, the dimeric nature of Sw. occidentalis
invertase reveals a unique active site cleft shaped by
both subunits that may be representative of other yeast enzymes
reported to be multimeric. Binding of the tetrasaccharide nystose
and the polymer inulin was explored by docking analysis,
which suggested that medium size and long substrates are recognized
by residues from both subunits. The identified residues
were mutated, and the enzymatic activity of the mutants against
sucrose, nystose, and inulin were investigated by kinetic analysis.
The replacements that showed the largest effect on catalytic
efficiency were Q228V, a residue putatively involved in nystose
and inulin binding, and S281I, involved in a polar link at the
dimer interface. Moreover, a significant decrease in catalytic
efficiency against inulin was observed in the mutants Q435A
and Y462A, both located in the -sandwich domain of the second
monomer. This highlights the essential function that oligomerization
plays in substrate specificity and assigns, for the first
time, a direct catalytic role to the supplementary domain of a
GH32 enzyme.
Fructans, the fru
Schwanniomyces occidentalis invertase is an extracellular
enzyme that hydrolizes sucrose and releases -fructose from
various oligosaccharides and essential storage fructan polymers
such as inulin. We report here the three-dimensional structure
of Sw. occidentalis invertase at 2.9A˚ resolution and its complex
with fructose at 1.9 A˚ resolution. The monomer presents a
bimodular arrangement common to other GH32 enzymes, with
an N-terminal 5-fold -propeller catalytic domain and a C-terminal
-sandwich domain for which the function has been
unknown until now. However, the dimeric nature of Sw. occidentalis
invertase reveals a unique active site cleft shaped by
both subunits that may be representative of other yeast enzymes
reported to be multimeric. Binding of the tetrasaccharide nystose
and the polymer inulin was explored by docking analysis,
which suggested that medium size and long substrates are recognized
by residues from both subunits. The identified residues
were mutated, and the enzymatic activity of the mutants against
sucrose, nystose, and inulin were investigated by kinetic analysis.
The replacements that showed the largest effect on catalytic
efficiency were Q228V, a residue putatively involved in nystose
and inulin binding, and S281I, involved in a polar link at the
dimer interface. Moreover, a significant decrease in catalytic
efficiency against inulin was observed in the mutants Q435A
and Y462A, both located in the -sandwich domain of the second
monomer. This highlights the essential function that oligomerization
plays in substrate specificity and assigns, for the first
time, a direct catalytic role to the supplementary domain of a
GH32 enzyme.
Fructans, the fru
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