Question

5. Human serum albumin (MW 66.5 kDa) is the most abundant protein in human blood plasma. Considering that the behavior of HAS in aqueous media can be satisfactory described as that of a sphere:

(Calculate the rotational correlation time of HAS in water at 37 ^oC.  To this end, consider that the specific volume of HAS is 0.73 mL/g, and that its hydration is 0.23 g H₂O per gram of protein. Given:  viscosity of water at 37 ^oC  = 0.691 centipoise; R = 8.31 x 10⁷erg Mol^-1K^-1.Calculate the anisotropy that can be expected from samples of HAS covalently tagged with the following two distinct fluorescent dyes. In the first sample HAS is tagged with a fluorescent dye that shows fundamental anisotropy equal to 0.37 and 18 ns lifetime. In the second sample HAS is tagged with a fluorescent dye that shows fundamental anisotropy equal to 0.40 and 1.0 ns lifetime. Which one of the HAS-tagged samples considered above would be preferable for use is studies dealing with the binding of HAS to other large biomolecules (if any). In other words, in which case the dynamic range associated with the experimental measurements would be larger. Explain your rational.  Here assume that the lifetime of the tagging dye does not change upon binding of the respective HAS-tagged adduct to other biomolecules.

Answer 1

Kinetics of binding of dyes at different sites of human serum albumin (HSA) has been studied by single molecule spectroscopy. the protein was immobilized on a glass sueface . to probe different binding site ( Hydrophilic and hydrophobic) two dyes. Coumarin 153(C153 neutral) and Rhodamine 6G(R6G, Cationic) were chosen. for the both the dyes Amajor 98% and minor 3% binding sites were detected .Rate constant of association and disassociation were simultaneouly determined from directly measuring fluctuations in florescence intensity. fluorecence life time at individual sites were obtained from brust integrated life time analysis. distributions of life time histograms for both the probes exhibit two maxima, which indicates the presence of two binding domains in the protein. unfolding of the protein has been studied by adding Guanidinium hydrochloride(GdnHCl) to the solution.