Dispersin B (DspB) from Aggregatibacter actinomycetemcomitans is
a p-hexosaminidase exhibiting biofilm detachment activity. A
series of beta-(1 -> 6)-linked N-acetyl-D-glucosamine thiophenyl
glycosides with degree of polymerisation (DP) of 2, 3, 4 and 5
were synthesized, and substrate specificity of DspB was studied
on the obtained oligosaccharides. For oligomer synthesis a 1+2,
2+2, 1+4 coupling strategy was applied, using bromo-sugars as
glycosyl donors. The formation of 1,2-trans interglycosidic bond
has been ensured by 2-phtalimido protecting group: chloroacetyl
group was installed to mask temporarily the 6-hydroxyl and
acetate esters were applied as permanent protecting groups.
Enzymatic studies revealed that DP of the GlcNAc oligomers
strongly affected the hydrolysis rate, and the hydrolytic
activity of DspB on the tetramer and pentamer have been found to
be approximately 10-fold higher than that of the dimer. This
fact indicates that four units are required for a strong binding
at the active centre of DspB. The role of aromatic amino acids
W237, Y187 and Y278 in substrate specificity and catalysis was
also examined using mutant enzymes. (C) 2011 Elsevier Ltd. All
rights reserved.
