HEXAFLUOROISOPROPANOL-INDUCED SECONDARY STRUCTURE PERTURBATION OF SOYBEAN AGGLUTININ

Abstract

Fluoroalcohols like 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) are widely used as cosolvent along with the biological solvent water to perturb the native protein molecules. The non native states obtained are of immense importance in the field of protein structure and folding, since these states may be present in the protein folding pathway or in the off pathway which leads to amyloid formation. In this study, HFIP-induced structure perturbation at secondary level of the tetrameric legume lectin, soybean agglutinin (SBA) is examined by far-UV circular dichroism (CD) spectroscopy. Like other member of the legume lectin family, native SBA is also an all β-sheet protein. Analysis of the far-UV CD spectra shows formation of α-helix rich conformations at the expense of native β-sheet in presence of higher concentration (50% or more) of HFIP. Visible aggregation is noticed at lower HFIP concentration (~10%) which disappears at higher concentration of HFIP with concomitant induction of the α-helical secondary structure. The results confirm about the helix propensity of amino acid sequence of SBA and helical intermediates may be involved in the early stage of its folding process.