Stability studies on a lipase from Bacillus subtilis in guanidinium chloride

Lipase from Bacillus subtilis is a "lidless" lipase that does not show interfacial activation. Due to exposure of the active site to solvent, the lipase tends to aggregate. We have investigated the solution properties and unfolding of the lipase in guanidinium chloride (GdmCl) to understand its aggregation behavior and stability. Dynamic light scattering (DLS), near- and far-UV circular dichroism, activity and intrinsic fluorescence of lipase suggest that the protein undergoes unfolding between 1 M and 2 M GdmCl. The polarity sensitive dye, 1,1',-bis-(4anilino)naphthalene-5,5"-disulfonic acid (bis-ANS), a probe for hydrophobic pockets, binds cooperatively to the native lipase. An intermediate populated in 1.75 M GdmCl that strongly binds bis-ANS was identified. Tendency of the native protein to aggregate in solution and specific binding to bis-ANS confirms that the lipase has exposed hydrophobic pockets and this surface hydrophobicity strongly influences the unfolding pathway of the lipase in GdmCl.