Vibrio vulnificus MO6-24/O has three genes annotated as
debranching enzymes or pullulanase genes. Among them,
the gene encoded by VVMO6_03032 (vvde1) shares a higher
similarity at the amino acid sequence level to the glycogen
debranching enzymes, AmyX of Bacillus subtilis (40.5%) and
GlgX of Escherichia coli (55.5%), than those encoded by the
other two genes. The vvde1 gene encoded a protein with a molecular
mass of 75.56 kDa and purified Vvde1 efficiently hydrolyzed
glycogen and pullulan to shorter chains of maltodextrin
and maltotriose (G3), respectively. However, it hydrolyzed
amylopectin and soluble starch far less efficiently,
and β-cyclodextrin (β-CD) only rarely. The optimal pH and
temperature of Vvde1 was 6.5 and 25°C, respectively. Vvde1
was a cold-adapted debranching enzyme with more than 60%
residual activity at 5°C. It could maintain stability for 2 days
at 25°C and 1 day at 35°C, but it destabilized drastically at
40°C. The Vvde1 activity was inhibited considerably by Cu2+,
Hg2+, and Zn2+, while it was slightly enhanced by Co2+, Ca2+,
Ni2+, and Fe2+. The vvde1 knock-out mutant accumulated more
glycogen than the wild-type in media supplemented with 1.0%
maltodextrin; however, the side chain length distribution of
glycogen was similar to that of the wild-type except G3, which
was much more abundant in the mutant. Therefore, Vvde1
seemed to debranch glycogen with the degree of polymerization
3 (DP3) as the specific target branch length. Virulence
of the pathogen against Caenorhabditis elegans was attenuated
significantly by the vvde1 mutation. These results suggest
that Vvde1 might be a unique glycogen debranching enzyme
that is involved in both glycogen utilization and shaping of
glycogen molecules, and contributes toward virulence of the
pathogen.
Citations
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