EPR and Circular Dichroism Solution Studies on the Interactions of Bovine Serum Albumin with Ionic Surfactants and β-Cyclodextrin

Abstract

The interactions of bovine serum albumin (BSA) with ionic surfactants (sodium dodecyl sulfate, SDS, and cetyltrimethylammonium bromide, CTAB) and β-cyclodextrin (β-CD) have been investigated by electron paramagnetic resonance (EPR) and circular dichroism measurements. The spin probe selected to report on the interaction of albumin with surfactants and/or β-CD was 4-N,N-dimethyl hexadecyl ammonium-2,2,6,6-tetramethylpiperidine-1-oxyl iodide (CAT16), on account of (a) its balance between electrostatic and hydrophobic character and (b) the ability of BSA to form complexes with various organic molecules. The distribution of the spin probe among different environments in solutions containing only BSA was confirmed by the existence of two components in the EPR spectra: one revealing a restricted mobility of the spin probe, attributed to the protein-spin probe complex, and another one showing free movement, attributed to the spin probe in solution. The presence of surfactants and/or β-CD alters the distribution of CAT16 between various compartments in each system. Formation of protein aggregates as a result of thermal denaturation was evidenced by the appearance of an immobilized component in the EPR spectrum. This component is not present in the EPR spectra of CAT16 in protein/surfactant or protein/cyclodextrin solutions. Circular dichroism spectra of BSA provided information about changes in the secondary structure of the protein induced by the presence of surfactants and/or cyclodextrin in solution. The results demonstrate that β-CD hinders the interaction between the employed surfactants and the protein. The cationic surfactant (CTAB) induces changes in protein conformation at a lower concentration compared to the anionic surfactant (SDS).

Interactions of Boron Clusters and their Derivatives with Serum Albumin

“…The CD spectrum of native BSA (25 °C, NaHCO 3 10 mM) exhibited two negative minima at 208 and 222 nm and a maximum at 192 nm, which is in good agreement with previous studies 51 and characteristic for proteins with high helical content. The CD spectra of native BSA in the presence of an increasing concentration of selected boron cluster (from 0 to 1000 molar excess) are represented in Fig.…”

Tuning of protein-surfactant interaction to modify the resultant structure

“…The ionic micelles are found to have the prolate ellipsoidal core-shell structure with semiminor axis, semimajor axis and shell thickness as 16.7, 28.6, and 5.0Å, respectively, for SDS and 16.7, 20.5, and 5.8Å, respectively, for DTAB. 28 The SDS and DTAB micelles have aggregation numbers of 95 and 68 with total charge on them −23.8 and +19.7 e.u., respectively. The lower effective size of the head group gives rise to a higher value of aggregation for SDS than DTAB.…”

“…These complexes are referred as bead-necklace structures [5][6][7]. There is also interest in knowing innovative ways by virtue of which an unfolded protein can fold back or prevent protein unfolding [16,[27][28][29]. The competition of electrostatic and hydrophobic interactions plays an important role for this purpose [30,31].…”

Reversibility of the interactions between a novel surfactant derived from lysine and biomolecules

“…This effect can be attributed to the stronger and more specific ␤-CD-LYCL hydrophobic interactions. ␤-CD does not associate to either the BSA or the ctDNA [49], but its non polar cavity has a high affinity for binding the hydrophobic chain of the LYCl. As a consequence, ␤-CD is able to strip the bound LYCl from the biomolecules.…”