Industrially important enzyme bovine liver catalase forms amyloid in the presence of 14-4-14 Gemini surfactant at physiological pH

Bovine liver catalase (BLC), a homotetramer (Mr = 28,000), is an industrially and pharmaceutically important enzyme. A cationic Gemini surfactant (tetramethylene-1,4-bis(dimethyltetradecylammonium bromide); 14-4-14) was found to induce aggregation in BLC, as confirmed by Rayleigh light scattering and dynamic light scattering up to ∼150 μM, at a critical micellar concentration (CMC) at physiological pH. On further increasing, the Gemini concentration aggregate disappeared. Secondary and tertiary structural studies confirmed that BLC structure perturbation occurs in two phases: first, loss of both secondary and tertiary structures till the CMC of 14-4-14; and second, recovery of the secondary structure above the CMC, unlike the tertiary structure that showed further solvent accessibility of tryptophan residues, which resulted in unfolding. Moreover, 14-4-14 may have unfolded the enzyme by either directly interacting or opening the hydrophobic patches or engineering solvent shells and reversibly disrupting helical structures until the concentration reaches the CMC. However, above the CMC, with the probable steric hindrance in 14-4-14 active groups due to polymerization, the BLC secondary structure recovered. The thioflavin T fluorescence and transmission electron microscopy results showed that the aggregates were amyloid in nature. Molecular docking analysis also confirmed that 14-4-14 interacted with BLC mainly through hydrophobic interactions, along with a minor contribution of electrostatic interactions. Thus, this study showed how to reverse the surfactant induced BLC amyloid at physiological pH and 298 K, which could be exploited industrially.