Journal of Physical Chemistry B, Vol.123, No.16, 3397-3408, 2019
Structure, Activity, and Dynamics of Human Serum Albumin in a Crowded Pluronic F127 Hydrogel
Structure, activity, and dynamics of a plasma protein, human serum albumin (HSA), inside a crowded environment of F127 gel are studied by circular dichroism (CD), fluorescence correlation spectroscopy (FCS), and picosecond time-resolved fluorescence spectroscopy. For this purpose, the protein is covalently labeled by a maleimide dye, 7-(diethylamino)-3-(4-maleimidylphenyl)-4-methyl-coumarin (CPM). The circular dichroism (CD) spectra suggest that the protein is more structured in the gel reflecting about the biological activities of the protein. FCS results demonstrate that compared to that in bulk water (buffer solution), translational diffusion is about 59 times slower inside the F127 gel. This indicates higher translational friction (viscosity) sensed by the probe (CPM). On the contrary, rotational relaxation (and hence, rotational friction) is more or less similar in F127 gel and in bulk water. FCS results further indicate that the time scales of conformational relaxation of the protein are substantially slow inside the crowded environment of F127 gel. The fast component of conformational relaxation is retarded by similar to 55 times, and the slow component by similar to 20 times. Fluorescence maximum of CPM bound to HSA show a similar to 5 nm red shift, implying that the microenvironment of the probe, CPM, is more polar inside the gel. Solvation dynamics of CPM-labeled HSA inside the gel ( similar to 300 ps) is faster compared to that for the protein in bulk water ( similar to 600 ps).