Background: Pullulanase is broadly used in saccharification process for glucose, maltose,
maltotriose, and fructose production. The in silico investigation can be a useful approach to
screen an enzyme with suitable characteristics for application in industry.
Objective: The aim of this study was an in silico
characterization and functional analysis of pullulanases
from different Bacillus
Method: A total number of 38 amino acid sequences of pullulanase were selected from different
species, and were investigated from the view of physiochemical properties, phylogenetic
relation, and domain architecture.
Results: Computational analyses showed that the pI values of the pullulanases were in the range of
4-7, which indicated that the enzyme is active in acidic to neutral environments. The pI value
greater than 7 belongs to pullulanase of Bacillus psychrosaccharolyticus and Bacillus flexus (8.19
and 8.55, respectively), which indicated the basic properties of the enzymes in these two species.
Their aliphatic indexes were in the range of 68-92. The pullulanase of Bacillus vireti had the highest
aliphatic index and thermostability value. The enzymes half-lives were more than 16 h, except
for Bacillus subtilis and Bacillus amyloliquefaciens (<5 h). All species had several domains with
common α -amylase catalytic motif containing conserved Glu/Asp residues. Four domains were
observed in the tertiary structure of Bacillus vireti pullulanase that were built by Swiss-model
server. Two domains, CBM and α-amylase, were conserved among the studied species.
Conclusion: Our study revealed that the Bacillus vireti
pullulanase had the higher thermostability
and half-life compared to the other species. Therefore, pullulanase of Bacillus vireti
is suggested as
a suitable candidate for industrial usages. In this case, investigating the physiochemical characterstics,
phylogenetic relation, secondary and tertiary structures of the enzyme can help us to improve
the properties of enzyme that is important for industrial applications.