Ionization of tyrosine residues in human serum albumin and in its complexes with bilirubin and laurate

Synergistic effect of chlorogenic acid and vitamin D3 (cholecalciferol) on in-vitro glycation may assist in prevention of polycystic ovarian syndrome (PCOS) progression - A biophysical, biochemical and in-silico study

Advanced glycation end products (AGEs) are formed through non-enzymatic glycation, that have been linked to various diseases, including polycystic ovarian syndrome (PCOS) playing a critical role leading to secondary comorbidities such as diabetes-related problems, cardiovascular complications, infertility, etc. As a result, there has been a lot of research into AGE-inhibiting phytochemicals for the remediation and obstruct progression of glycation-related illnesses. The current study is based on in-vitro protein model, in which human serum albumin have been used to investigate the cumulative effect of chlorogenic acid (CGA) and cholecalciferol (vitamin D) on glycation and evaluate their inhibitory impact on AGEs production in the presence of methylglyoxal. Through the application of several biochemical and biophysical techniques, we were able to examine the synergistic impact of both the compounds on albumin structure and its biochemical properties during different stages of glycation. According to Nitro-blue tetrazolium assay results indicate that CGA and vitamin D inhibited fructosamine (early glycation product) production. Moreover, free thiol and lysine residues were significantly increased whereas protein carbonyl levels were significantly decreased. Additive effect of CGA and vitamin D were associated with reduced AGEs fluorescence and increased tryptophan and tyrosine fluorescence. Amadori-albumin after treatment showed some evidence of regaining its alpha-helicity as measured by far-UV CD spectrum. Furthermore, secondary structural alterations were confirmed by Fourier transform infrared spectroscopy (FTIR). ANS (1-anilinonaphthalene-8-sulfonic acid) fluorescence spectra also displayed less revelation of hydrophobic patches. Bilirubin binding capacity was also restored which showed functional recovery of HSA. The electrophoretic mobility was also restored which is portrayed by SDS-PAGE. Additionally, to predict the anti-aggregation potential of CGA and vitamin D, congo red assay and ThT fluorescence was performed which reveal low aggregate formation after treatment. These results corroborated with scanning electron microscopy and confocal microscopy. Docking and simulation results also reveal spontaneous binding of CGA and vitamin D on subdomain IIA of HSA favoring their binding thermodynamically. All the findings suggest that chlorogenic acid and cholecalciferol given in combination might help in prevention of PCOS progression and its related complications.

PHEPS: web-based pH-dependent Protein Electrostatics Server

PHEPS (pH-dependent Protein Electrostatics Server) is a web service for fast prediction and experiment planning support, as well as for correlation and analysis of experimentally obtained results, reflecting charge-dependent phenomena in globular proteins. Its implementation is based on long-term experience (PHEI package) and the need to explain measured physicochemical characteristics at the level of protein atomic structure. The approach is semi-empirical and based on a mean field scheme for description and evaluation of global and local pH-dependent electrostatic properties: protein proton binding; ionic sites proton population; free energy electrostatic term; ionic groups proton affinities (pK_a,i) and their Coulomb interaction with whole charge multipole; electrostatic potential of whole molecule at fixed pH and pH-dependent local electrostatic potentials at user-defined set of points. The speed of calculation is based on fast determination of distance-dependent pair charge-charge interactions as empirical three exponential function that covers charge–charge, charge–dipole and dipole–dipole contributions. After atomic coordinates input, all standard parameters are used as defaults to facilitate non-experienced users. Special attention was given to interactive addition of non-polypeptide charges, extra ionizable groups with intrinsic pK_as or fixed ions. The output information is given as plain-text, readable by ‘RasMol’, ‘Origin’ and the like. The PHEPS server is accessible at .

Palmitate and stearate binding to human serum albumin. Determination of relative binding constants

Multiple binding equilibria of two apparently insoluble ligands, palmitate and stearate, to defatted human serum albumin were studied in a 66 mM sodium phosphate buffer (pH 7.4) at 37 degrees C, by determination of dialytic exchange rates of ligands among identical equilibrium solutions. The experimental data were analysed by a computerised curve fitting procedure using equilibrium equations for multiple binding of ligands, containing relative binding constants, valid whether the ligands are truly insoluble or are slightly soluble and irrespective of aggregation in aqueous solution. A best-fit set of relative binding constants was found, and subsequently 30 sets of acceptable constants for each set of data in order to evaluate the variation. The data were first fitted by the relative Scatchard's equation, then by the relative, stoichiometric equation. Scatchard's equation is deduced on the presumption that cooperativity is absent while the stoichiometric equation is valid even when cooperativity is present. It was found with palmitate as well as with stearate that the two equations fitted the data equally well, and it was concluded that the observations were compatible with absence of cooperativity. The relative Scatchard binding constants were converted to relative, stoichiometric constants and it was found that the variations of the latter were slight.

New procedure for analysing drug binding data, exemplified by warfarin binding to human serum albumin

Determination of binding constants for multiple binding of a ligand usually results in highly variable figures. We have found that the variations depend mainly upon cooperativity of ligand binding, and that cooperativity is generally absent on binding to human serum albumin. When this is taken into account it becomes possible to obtain binding constants with only slight variation. A computerized curve fitting procedure for analysing binding data has been established consisting of the following steps. (1) Fitting of Scatchard's equation to observed binding equilibrium data to obtain a best-fit set of Scatchard binding constants. (2) Repetition of the fitting procedure, not to obtain a best fit but to generate 30 acceptable sets of Scatchard binding constants. (3) Fitting of Adair's equation to the observed points to obtain a best fit. If the sum of weighted and squared deviations is significantly smaller than the fitting of Scatchard's equation, cooperativity should be considered. If not, cooperativity cannot be demonstrated and the binding constants obtained by fitting Scatchard's equation can be accepted, with the variations found. (4) Final transformation of all Scatchard constants to Adair's. To illustrate the method warfarin data obtained by equilibrium dialysis was used.