Interactions of Globular Proteins with Surfactants Studied with Fluorescence Probe Methods

Abstract

Steady-state and dynamic fluorescence measurements were used to investigate the interactions and structures of complexes formed between bovine serum albumin (BSA) and anionic, cationic, and nonionic surfactants: sodium dodecyl sulfate (SDS), N-cetyl-N,N,N-trimethylammonium bromide (CTAB), and octaoxyethylene glycol n-dodecyl ether (C12E8), respectively. The lysozyme (Lys)−SDS complex was also studied. The measurements were carried out at different pH's and ionic strengths. In all systems, micelle-like clusters adsorbed on protein were evidenced. The average aggregate numbers are smaller than those of free micelles and are not strongly influenced by pH and ionic strength. The fluorescence lifetime of pyrene in BSA/surfactant complexes was constant at low surfactant concentrations, started to decrease at approximately the same protein−surfactant ratio (0.15 mM BSA/1 mM surfactant) regardless of the surfactant type or pH buffer, and, at high surfactant concentrations, merged to the lifetime values corresponding to free micelles. The results of the fluorescence techniques support a “necklace and bead” model of the complex for BSA/surfactant systems, with protein wrapped around the micelles. For the Lys/SDS complex, the model essentially is the same; however, some differences, due to their different sizes, appear. Lysozyme is smaller and more rigid and does not wrap up well around the micelle.

Biopolymer Surfactant Interactions

“…DLS studies of CTABGelatin interaction [74,75] showed that beyond critical aggregation concentration gelatin -CTAB complexes were observed to grow significantly and were in equilibrium with CTAB micelles. The micellar shapes were found to be oblate ellipsoidal for CTAB micelles which were explained through the necklace -bead model through co-operative bonding [76]. Hydrophobic interaction may be operating between the hydrophobic part of CTAB and hydrophobic sites on the gelatin chain.…”

“…An abrupt increase in, ηr, can be due to the incorporation of halide ion leading to the screening of the electrostatic interaction of surfactant head groups. Decreased head group repulsion favors closer packing of the surfactant monomers and hence induces sphere → rod transition in micelles [76,77]. At higher [CTAB+ NaCl], further increase in size is observed due to formation of polymer -micelle complex.…”

Research progress of surfactant

“…Because human serum albumin is physiologically important and easy to isolate and purify, it is often used as a model globulin to study its interaction with surfactants [15][16][17][18]. The thermodynamic properties of the interaction of HSA with two quaternary ammonium gemini surfactants in buffer solution (pH =7.0) were studied by isothermal 030008-2 titration calorimetry at 298.15 K. The results showed that the secondary structure of HSA was changed by the addition of surfactants.…”

Giant Extracellular Hemoglobin of Glossoscolex paulistus: An excellent Prototype of Biosensor and Blood Substitute

“…Surfactants are widely employed in biochemistry and biotechnology for the purpose of protein solubilization, purification, characterization, and protein structure determination (Miksovska, et al, 2006). Surfactant-protein interactions are very common in the fields of medicine, chemistry, biology and so on (Liu et al, 2007;van der Veen et al, 2004;Orioni et al, 2006;Vasilescu et al, 1999;Stenstam et al, 2003). Many approaches have been focused such as the kind of protein-surfactant interaction, the influence of the aggregation state of the surfactant (monomer, pre-micellar aggregate and micelle) on the protein structure, the properties of the surfactant-protein system, the characterization of the interaction sites on the protein surface, the identification of the intermediate protein conformations, etc (Liu et al, 2007;Liu et al, 2005;Ajloo et al, 2002).…”