Solvent perturbation was used to study variations in structure of Arisaema helliborifolium
lectin (AHL) with the help of circular dichroism (CD), intrinsic fluorescence (IF), extrinsic fluorescence,
quenching and dynamic light scattering (DLS). AHL was studied under acidic, alkaline and 6
M guanidine hydrochloride (GuHCl) equilibrium states. Three structural states were identified for
AHL at different conditions, that are native (N; pH 7.0), molten globule (MG; pH 2.0) and unfolded
(U; pH 12.0). CD analysis revealed that 50% of secondary structure of AHL was -sheet component.
A complete loss of secondary structure was observed at GuHCl treatment. The tertiary structural changes as studied by
changes in microenvironment of trp residues also suggested a pH induced MG state as in case of CD. Parameter-A analysis
pointed at the multi-step unfolding process of lectin under varying pH (pH 1-13). A comparision of CD and IF data
further indicated that different pathways were followed for secondary and tertiary structure unfolding. Tryptophans of native
AHL were only partially exposed to solvent belonging to Class II. Hydrodynamic diameter (Dh ) measurements of
AHL via DLS also confirmed of a pH induced molten globule. A thermally induced molten globule was identified for
AHL between 54-60 °C as monitored by DLS. An irreversible thermal denaturation was observed with the formation of a
large aggregate. The Dh of AHL at neutral pH was confirmed by transmission electron microscopy (TEM).
Keywords: Circular dichroism, Dynamic light scattering, Fluorescence, Guanidine hydrochloride, Lectin, Molten globule, pH
denaturation, Thermal unfolding, Transmission electron microscopy.
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