Dynamic and thermodynamic effects of glycerol on bovine serum albumin in aqueous solution: a tryptophan phosphorescence study

Nano-second protein dynamics of key residue at Position 38 in catechol-O-methyltransferase system: a time-resolved fluorescence study

Human catechol-O-methyltransferase, a key enzyme related to neurotransmitter metabolism, catalyses a methyl transfer from S-adenosylmethionine to catechol. Although extensive studies aim to understand the enzyme mechanisms, the connection of protein dynamics and enzyme catalysis is still not clear. Here, W38in (Trp143Phe) and W38in/Y68A (Trp143Phe with Tyr68Ala) mutants were carried out to study the relationship of dynamics and catalysis in nano-second timescale using time-resolved fluorescence lifetimes and Stokes shifts in various solvents. The comprehensive data implied the mutant W38in/Y68A with lower activity is more rigid than the ‘WT’−W38in, suggesting the importance of flexibility at residue 38 to maintain the optimal catalysis.

Dynamics of hemoglobin in human erythrocytes and in solution: influence of viscosity studied by ultrafast vibrational echo experiments

Ultrafast spectrally resolved stimulated vibrational echo experiments are used to measure the vibrational dephasing of the CO stretching mode of hemoglobin-CO (HbCO) inside living human erythrocytes (red blood cells), in liquid solutions, and in a glassy matrix. A method is presented to overcome the adverse impact on the vibrational echo signal from the strong light scattering caused by the cells. The results from the cytoplasmic HbCO are compared to experiments on aqueous HbCO samples prepared in different buffers, solutions containing low and high concentrations of glycerol, and in a solid trehalose matrix. Measurements are also presented that provide an accurate determination of the viscosity at the very high Hb concentration that is found inside the cells. It is demonstrated that the dynamics of the protein, as sensed by the CO ligand, are the same inside the erythrocytes and in aqueous solution and are independent of the viscosity. In solutions that are predominantly glycerol, the dynamics are modified somewhat but are still independent of viscosity. The experiments in trehalose give the dynamics at infinite viscosity and are used to separate the viscosity-dependent dynamics from the viscosity-independent dynamics. Although the HbCO dynamics are the same in the red blood cell and in the equivalent aqueous solutions, differences in the absorption spectra show that the distribution of a protein's equilibrium substates is sensitive to small pH differences.

Analysis of kinetics using a hybrid maximum-entropy/nonlinear-least-squares method: application to protein folding

A hybrid analysis that combines the maximum entropy method (MEM) with nonlinear least squares (NLS) fitting has been developed to interpret a general time-dependent signal. Data that include processes of opposite sign and a slow baseline drift can be inverted to obtain both a continuous distribution of lifetimes and a sum of discrete exponentials. Fits by discrete exponentials are performed with initial parameters determined from the distribution of lifetimes obtained with the MEM. The regularization of the parameter space achieved by the MEM stabilizes the introduction of each successive exponential in the NLS fits. This hybrid approach is particularly useful when fitting by a large number of exponentials. Revision of the MEM "prior" based on features in the data can improve the lifetime distribution obtained. Standard errors in the mean are estimated automatically for raw data. The results presented for simulated data and for fluorescence measurements of protein folding illustrate the utility and accuracy of the hybrid algorithm. Analysis of the folding of dihydrofolate reductase reveals six kinetic processes, one more than previously reported.