The role of hydrophobic interactions in the molten globule state of globular protein modulated by surfactants

In order to highlight the role of hydrophobic interactions in the molten globule (MG) state of globular protein modulated by surfactants, the interactions of bovine a-lactalbumin (alpha-LA) with alkyl trimethylammonium bromides (C(n)TAB, n = 10, 12, 14, and 16) have been studied by experimental and theoretical techniques. Isothermal titration calorimetry (ITC) showed that the enthalpy changes (Delta H) and area of the enthalpogram increased with increasing the chain length of C(n)TAB. The result of fluorescence, circular dichroism (CD) and H-1 nuclear magnetic resonance (NMR) spectrum suggested that C10TAB and C12TAB unfolded alpha-LA partially, C14TAB reconstructed protein with a native-like secondary structure content, and C16TAB induced an MG state alpha-LA. The SAXS results confirmed that the tertiary structure of a-LA was disrupted by C16TAB forming an MG state complex with a micelle-like structure even at the surfactants concentrations below CMC. As indicated by MD results, the beta-domain and unstructured region(s) were involved in the MG state alpha-LA modulated by C(n)TAB. This work not only provides molecular insights into the role of hydrophobic interactions in the MG state of a globular protein but also helps understand the mechanism of preparing a-LA based biomacromolecule modulated by hydrophobic interactions.