Comparative studies on the heterogeneity of plasma-derived and recombinant human albumins in laboratory use

Structural and mechanistic insights into the transport of aristolochic acids and their active metabolites by human serum albumin

Aristolochic acids I and II (AA-I/II) are carcinogenic principles of Aristolochia plants, which have been employed in traditional medicinal practices and discovered as food contaminants. While the deleterious effects of AAs are broadly acknowledged, there is a dearth of information to define the mechanisms underlying their carcinogenicity. Following bioactivation in the liver, N-hydroxyaristolactam and N-sulfonyloxyaristolactam metabolites are transported via circulation and elicit carcinogenic effects by reacting with cellular DNA. In this study, we apply DNA adduct analysis, X-ray crystallography, isothermal titration calorimetry, and fluorescence quenching to investigate the role of human serum albumin (HSA) in modulating AA carcinogenicity. We find that HSA extends the half-life and reactivity of N-sulfonyloxyaristolactam-I with DNA, thereby protecting activated AAs from heterolysis. Applying novel pooled plasma HSA crystallization methods, we report high-resolution structures of myristic acid-enriched HSA (HSAMYR) and its AA complexes (HSAMYR/AA-I and HSAMYR/AA-II) at 1.9 Å resolution. While AA-I is located within HSA subdomain IB, AA-II occupies subdomains IIA and IB. ITC binding profiles reveal two distinct AA sites in both complexes with association constants of 1.5 and 0.5 · 106 M-1 for HSA/AA-I versus 8.4 and 9.0 · 105 M-1 for HSA/AA-II. Fluorescence quenching of the HSA Trp214 suggests variable impacts of fatty acids on ligand binding affinities. Collectively, our structural and thermodynamic characterizations yield significant insights into AA binding, transport, toxicity, and potential allostery, critical determinants for elucidating the mechanistic roles of HSA in modulating AA carcinogenicity.

Comprehensive profiling and kinetic studies of glycated lysine residues in human serum albumin

Lysine residues of proteins slowly react with glucose forming Amadori products. In hyperglycemic conditions, such as diabetes mellitus, this non-enzymatic glycation becomes more pervasive causing severe medical complications. The structure and conformation of a protein predisposes lysine sites to differing reactivity influenced by their steric availability and amino acid microenvironment. The goal of our study was to identify these sites in albumin and measure glycation affinities of lysine residues. We applied a bottom-up approach utilizing a combination of three LC-MS instruments: timsTOF, Orbitrap, and QTRAP. To prove applicability to samples of varying glycemic status, we compared in vitro glycated and non-glycated HSA, as well as diabetic and non-diabetic individual samples. The analysis of lysine glycation affinities based on peptide intensities provide a semi-quantitative approach, as the results depend on the mass spectrometry platform used. We found that glycation levels based on multiple reaction monitoring (MRM) quantitation better reflect individual glycemic status and that the glycation percentage for each site is in linear relation to all other sites. To develop an approach which more accurately reflects glycation affinity, we developed a kinetics model which uses results from stable isotope dilution HPLC-MRM methodology. Through glycation of albumin at different glucose concentrations, we determine the rate constants of glycation for every lysine residue by simultaneous comparative analysis.

Blood serum denaturation profile examined by differential scanning calorimetry reflects the effort put into ultramarathon by amateur long-distance runners

The impact of participation in the ultramarathon on the health and mental and physical condition is very complex. Undoubtedly, exercise brings many benefits but also involves health risks. Especially such an extreme effort as the one associated with finishing the ultramarathon run, can be dangerous to the health of the runner. With the variety of possible biomarkers of excessive fatigue that threaten health and life, a question arises which of them are the best and which should be considered in amateur long-distance runners showing particularly high individual variability. In this study differential scanning calorimetry (DSC) has been applied to show the overall effect of the 12-h run on blood sera of participants. Serum samples were obtained from the blood of ten male amateur long-distance runners, collected before and immediately after the run. Distinct changes in the shape of DSC curves have been observed for serum after finishing the run relative to pre-race serum. Statistically significant differences between stages "before" and "after" ultramarathon running have been found for parameters of the endothermic transition associated with denaturation of serum proteins. An increase in the temperature (from 70.9 ± 0.9 to 75.8 ± 2.9 °C) and excess heat capacity (from 0.859 ± 0.201 to 1.102 ± 0.226 Jg-1 °C-1) at peak maximum, the enthalpy of serum denaturation (from 18.55 ± 6.52 to 22.08 ± 5.61 Jg^-1) and the first moment of the thermal transition with respect to the temperature (from the value of 67.0 ± 2.1 to 72.6 ± 2.1 °C) has been observed. These results show a clear impact of running an ultramarathon on the participant's blood serum.

Analysis of the conformation and thermal stability of the high-affinity IgE Fc receptor β chain polymorphic proteins

The high-affinity IgE Fc receptor (FcεRI) β chain acts as a signal amplifier through the immunoreceptor tyrosine-based activation motif in its C-terminal intracellular region. Polymorphisms in FcεRI β have been linked to atopy, asthma, and allergies. We investigated the secondary structure, conformation, and thermal stability of FcεRI β polymorphic (β-L172I, β-L174V, and β-E228G) proteins. Polymorphisms did not affect the secondary structure and conformation of FcεRI β. However, we calculated Gibbs free energy of unfolding (ΔGunf) and significant differences were observed in ΔGunf values between the wild-type FcεRI β (β-WT) and β-E228G. These results suggested that β-E228G affected the thermal stability of FcεRI β. The role of β-E228G in biological functions and its involvement in allergic reactions have not yet been elucidated in detail; therefore, differences in the thermal stability of β-E228G may affect the function of FcεRI β.

Design of protein homocystamides with enhanced tumor uptake properties for (19)F magnetic resonance imaging

Straightforward and reliable tools for in vivo imaging of tumors can benefit the studies of cancer development, as well as contribute to successful diagnosis and treatment of cancer. (19)F NMR offers an exceptional quantitative way of in vivo imaging of the infused agents because of the lack of (19)F signals from the endogenous molecules in the body. The purpose of this study is to develop molecular probes with appropriate NMR characteristics and the biocompatibility for in vivo applications using (19)F MRI. We have studied the reaction between perfluorotoluene and homocysteine thiolactone resulting in the formation of N-substituted homocysteine thiolactone derivative. It has been shown that the reaction occurs selectively at the para position. This fluorine-labeled homocysteine thiolactone has been employed for the introduction of a perfluorotoluene group as a (19)F-containing tag into human serum albumin. The modified protein has been studied in terms of its ability to aggregate and promote the formation of free radicals. By comparing the properties of N-perfluorotoluene-homocystamide of albumin with N-homocysteinylated albumin, it has been revealed that blocking of the alpha-amino group of the homocysteine residue in the fluorinated albumin conjugate inhibits the dangerous aggregation process, as well as free radical formation. A dual-labeled albumin-based molecular probe for (19)F MRI and fluorescence microscopy has been obtained by functionalizing the protein with both maleimide of a fluorescent dye and a fluorinated thiolactone derivative. The incubation of cells with this conjugate did not reveal any significant reduction in cell viability with respect to the parent albumin. The perfluorotoluene-labeled albumin has been demonstrated to act as a promising agent for in vivo (19)F MRI.