Protein-surfactant interactions: a tale of many states.

Spectroscopic analysis on the binding interaction of biologically active pyrimidine derivative with bovine serum albumin.

A simple intramolecular charge transfer (ICT) compound, 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME), has been documented to be a potential molecular reporter for probing microheterogeneous environments of a model transport protein bovine serum albumin (BSA) using spectroscopic techniques. Meteoric modifications to the emission profile of DPDAME upon addition of BSA come out to be a result of its binding to hydrophobic subdomain IIA. The highly polarity-sensitive ICT emission of DPDAME is found to be a proficient extrinsic molecular reporter for efficient mapping of native, intermediate, unfolded, and refolded states of the protein. Experimental data coupled with a reinforcing support from theoretical simulation using CHARMM22 software confirm the binding site of the probe to be the subdomain IIA of BSA, while FRET study reveals a remarkably close approach of our extrinsic molecular reporter to Trp-212 (in domain IIA): the distance between DPDAME and Trp-212 is 1.437 nm. The caliber of DPDAME as an external fluorescence marker also extends to the depiction of protein-surfactant (BSA-SDS) interaction to commendable fruition. Additionally, the protective action of small amounts of SDS on urea-denatured protein is documented by polarity-sensitive ICT emission of the probe. The present study also reflects the enhancement of the stability of BSA with respect to chemically induced denaturation by urea as a result of binding to the probe DPDAME.

Exploring hydrophobic subdomain IIA of the protein bovine serum albumin in the native, intermediate, unfolded, and refolded states by a small fluorescence molecular reporter

Fluorescence probing of albumin-surfactant interaction.

The effect of the anionic surfactant sodium dodecyl sulfate (SDS) on the protein human serum albumin (HSA) was studied using steady-state spectroscopy, time-resolved measurements, and circular dichroism spectroscopy. The binding of SDS to the domain IIA of HSA, housing the single tryptophan amino acid residue (Trp214), was monitored, and it was found that this addition of the surfactant takes place in a sequential manner depending upon the concentration of the added surfactant. Both fluorescence intensity and lifetimes of HSA decreased with the increasing concentration of SDS, and the surfactant molecules serve the role of a quencher for the fluorescence of Trp214. Circular dichroism data also support the structural changes induced by SDS. The 17 disulfide bridges present in HSA provide the necessary structural rigidity to the protein. Stern-Volmer plots and thermodynamic parameters have been used to characterize the sequential binding of SDS to HSA, and these parameters not only confirm that the binding is spontaneous in nature but also is quite strong, depending on the concentration of the added surfactant.

Spectroscopic Probing of the Microenvironment in a Protein−Surfactant Assembly

Upon the addition of small amounts of sodium dodecyl sulfate (SDS), the helicity of human serum albumin (HSA), lost in the urea denaturation, was mostly recovered. The profile of the recovery differed depending on the urea concentration. Then the urea concentrations were divided into three ranges:  [1] a range below 3 M where the helicity only decreased as in the absence of urea (the helicity decreased down to 49% in the SDS solution); [2] a range between 4 and 8 M where the helicity initially increased up to 66% (this was the same as in the native state) and then sharply decreased; [3] a range above 9 M where the helicity only increased with an increase in added SDS concentration. When SDS was added prior to the urea denaturation, the same helicity was obtained at each surfactant concentration. Thus the SDS denaturation finally predominates over the urea denaturation. In the middle range, profiles of the structural change were rather complicated. The increase and decrease of helicity were accomplished be...

Re-formation of the Helical Structure of Human Serum Albumin by the Addition of Small Amounts of Sodium Dodecyl Sulfate after the Disruption of the Structure by Urea. A Comparison with Bovine Serum Albumin

The interaction between sodium dextran sulfate (DxS) and alkyltrimethylammonium bromides was studied by means of potentiometric titration and electrophoretic light scattering methods in the phospha...

Yoshiko Moriyama and

Papers

Re-formation of the Helical Structure of Human Serum Albumin by the Addition of Small Amounts of Sodium Dodecyl Sulfate after the Disruption of the Structure by Urea. A Comparison with Bovine Serum Albumin

Electrophoretic Behavior of Complexes between Sodium Dextran Sulfate and Cationic Surfactants