AmyP is an α-amylase which shows preferential degradation to soluble starch. In this
substrate preference its Starch Binding Domain (SBD), which was recently assigned to a new
Carbohydrate Binding Module (CBM) family 69, plays an important role. In the present study,
the SBD of AmyP (AmyP-SBD) was recombinantly expressed, purified, and structurally characterized.
Using Circular Dichroism (CD), intrinsic fluorescence, and nuclear magnetic resonance
(NMR) spectroscopy, the structures of AmyP-SBD in the absence and presence of substrate analogue
β-cyclodextrin were measured. The results intriguingly showed that free form AmyP-SBD
is partially unfolded, like a compact molten globule, and could be induced by the ligand to fold
into a relatively rigid state. Further structure determination for folded AmyP-SBD revealed a topology
distinctive from those of SBDs from other CBM families. Our data indicate AmyP-SBD is
a structurally novel SBD, and this may be helpful for understanding the properties of AmyP-SBD
and CBM69 and elucidation of functioning mechanism of AmyP.
Keywords: Starch binding domain, molten globule, ligand induced folding, carbohydrate binding module family 69, AmyP,
nuclear magnetic resonance.
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