Introduction: Interaction of surfactants with proteins can decipher important information
regarding the stability and behavior of proteins. For multi-domain proteins, these interactions vary
domain wise and these details are crucial in understanding the contribution of different domains of
the protein in its overall activity.
Objective: The objective of the present work is to study the interaction of surfactants with domain
III of Human Serum Albumin (HSA) and to compare the same with the global interaction.
Methods: Interaction of the anionic Sodium Dodecyl Sulphate (SDS) and the Cationic
Cetyltrimethylammonium Bromide (CTAB) surfactants with domain III of Human Serum Albumin
(HSA) has been studied using 8-Anilino-1-Naphthalene-Sulphonate (ANS) as a fluorescent marker.
Circular Dichroism (CD) spectroscopy has been used to study the protein-surfactant interaction for
the overall protein.
Results: SDS is found to interact sequentially with domain III of HSA having two detectable intermediate
states in the binding process. In case of CTAB, we have observed only one intermediate
state for its interaction with domain III. Although Quantum yield measurement can reflect the presence
of such intermediate state, the overall conformational change of the HSA on addition of surfactants,
studied by Circular Dichroism (CD) spectroscopy, and the ANS-Trp distance measurement
by FRET could not resolve the presence of such intermediate states. The esterase activity of
HSA in presence of different amount of surfactants is also in accordance with our above observation.
Conclusion: The interaction of both the surfactants with HSA is found to be sequential in nature.
The most important conclusion revealed from our study is that the nature of protein-surfactant interaction
is not same throughout the entire protein. Our study reveals that different parts of the
multi-domain HSA have different affinity to the surfactant molecules.