Pseudo-esterase activity of human albumin: slow turnover on tyrosine 411 and stable acetylation of 82 residues including 59 lysines

Effective parallel evaluation of molecular design, expression and bioactivity of novel recombinant butyrylcholinesterase medical countermeasures

Current medical countermeasures (MCMs) for nerve agent poisoning have limited efficacy, and can cause serious adverse effects, prompting the requirement for new broad-spectrum therapeutics. Human plasma-derived butyrylcholinseterase (huBChE) is a promising novel bioscavenger MCM which has shown potential in animal studies, however, is economically prohibitive to manufacture at scale. This study addresses current challenges for the economical production of a bioactive and long-acting recombinant huBChE (rBChE) in mammalian cells by being the first to directly compare novel rBChE design strategies. These include co-expression of a proline rich attachment domain (PRAD) and fusion of BChE with a protein partner. Additionally, a pre-purification screening method developed in this study enables parallel comparison of the expression efficiency, activity and broad-spectrum binding to nerve agents for ten novel rBChE molecular designs. All designed rBChE demonstrated functionality to act as broad-spectrum MCMs to G, V and A series nerve agents. Expression using the ExpiCHO™ Max protocol provided greatest expression levels and activity for all constructs, with most rBChE expressing poorly in Expi293™. Fc- or hSA-fused rBChE significantly outperformed constructs designed to mimic huBChE, including PRAD-BChE, and proved an effective strategy to significantly improve enzyme activity and expression. Choice of protein partner, directionality and the addition of a linker also impacted fusion rBChE activity and expression. Overall, hSA fused rBChE provided greatest expression yield and activity, with BChE-hSA the best performing construct. The purified and characterised BChE-hSA demonstrated similar functionality to huBChE to be inhibited by GD, VX and A-234, supporting the findings of the pre-screening study and validating its capacity to assess and streamline the selection process for rBChE constructs in a cost-effective manner. Collectively, these outcomes contribute to risk mitigation in early-stage development, providing a systematic method to compare rBChE designs and a focus for future development.

Computational Study of Molecular Mechanism for the Involvement of Human Serum Albumin in the Renin-Angiotensin-Aldosterone System

Human serum albumin (HSA) is an endogenous inhibitor of angiotensin I-converting enzyme (ACE) and, thus, plays a key role in the renin-angiotensin-aldosterone system (RAAS). However, little is known about the mechanism of interaction between these proteins, and the structure of the HSA-ACE complex has not yet been obtained experimentally. The purpose of the presented work is to apply computer modeling methods to study the interaction of HSA with ACE in order to obtain preliminary details about the mechanism of their interaction. Ten possible HSA-ACE complexes were obtained by the procedure of macromolecular docking. Based on the number of steric and polar contacts between the proteins, three leading complexes were selected, the stabilities of which were then tested by molecular dynamics (MD) simulation. Based on the results of MD simulation, the two most probable conformations of the HSA-ACE complex were selected. The analysis of these conformations revealed that the processes of oxidation of the thiol group of Cys34 of HSA and the binding of albumin to ACE can reciprocally affect each other. Known point mutations in the albumin molecules Glu82Lys, Arg114Gly, Glu505Lys, Glu565Lys and Lys573Glu can also affect the interaction with ACE. According to the result of MD simulation, the known ACE mutations, albeit associated with various diseases, do not affect the HSA-ACE interaction. A comparative analysis was performed of the resulting HSA-ACE complexes with those obtained by AlphaFold 3 as well as with the crystal structure of the HSA and the neonatal Fc receptor (FcRn) complex. It was found that domains DI and DIII of albumin are involved in binding both ACE and FcRn. The obtained results of molecular modeling outline the direction for further study of the mechanisms of HSA-ACE interaction in vitro. Information about these mechanisms will help in the design and improvement of pharmacotherapy aimed at modulation of the physiological activity of ACE.

Excreted albumin of diabetic microalbuminuria cases exhibits pseudo esterase activity: A new way to explore microalbuminuria, perhaps with more information

BACKGROUND

Microalbuminuria is associated with several clinical conditions of public health concern. Particularly in diabetic patients, there is routine microalbuminuria screening to understand whether the renal complication has progressed to the microalbuminuria stage or not. Therefore, microalbuminuria detection is a matter of considerable interest. For such detection, the clinical labs rely on immunochemical methods. Nevertheless, the immunochemical methods are believed to be less sensitive for the purpose. So, the need arises for continuous research in the field. We believe that pseudoesterase activity of the excreted albumin in microalbuminuria cases is a potential target. This aspect is investigated here and it is shown that the excreted albumin in diabetic microalbuminuria cases retains its pseudoesterase activity, unlike the overt albuminuria cases.

METHODS

The cases of diabetic nephropathy and healthy controls were included in the study. The patients were divided into diabetic controls microalbuminuria, and overt albuminuria group considering the albumin to creatinine ratio (ACR). The urinary proteins of the cases were isolated by centrifugation. The obtained protein pellet was then checked for pseudoesterase activity by electrophoretic and fluorescence-based methods. The CD spectroscopy and LC-MS study was carried out to show the suitability of the substrate for the detection of albumin pseudoesterase activity. To further, understand the structure-function relation, molecular docking studies were carried out.

RESULTS

From the CD and LC-MS study the suitability of the used substrate was confirmed. The electrophoretic and fluorescence study showed that the protein of the microalbuminuria group retained the pseudoesterase activity whereas the same is lost in the overt albuminuria group. The molecular docking studies indicated that a change in albumin structure may result in a change in its pseudoesterase activity.

CONCLUSION

The urinary protein of diabetic microalbuminuria cases exhibits pseudoesterase activity. It distinguishes the excreted protein in the diabetic albuminuria group and the overt albuminuria group. This is the first study that showed the retention of pseudoesterase property in excreted albumin. Further, in this study a simple test is developed that distinguishes the excreted albumin in the microalbuminuria group and overt albuminuria group.

Sequence-encoded bioactive protein-multiblock polymer conjugates via quantitative one-pot iterative living polymerization

Protein therapeutics are essential in treating various diseases, but their inherent biological instability and short circulatory half-lives in vivo pose challenges. Herein, a quantitative one-pot iterative living polymerization technique is reported towards precision control over the molecular structure and monomer sequence of protein-polymer conjugates, aiming to maximize physicochemical properties and biological functions of proteins. Using this quantitative one-pot iterative living polymerization technique, we successfully develop a series of sequence-controlled protein-multiblock polymer conjugates, enhancing their biostability, pharmacokinetics, cellular uptake, and in vivo biodistribution. All-atom molecular dynamics simulations are performed to disclose the definite sequence-function relationship of the bioconjugates, further demonstrating their sequence-encoded cellular uptake behavior and in vivo biodistribution in mice. Overall, this work provides a robust approach for creating precision protein-polymer conjugates with defined sequences and advanced functions as a promising candidate in disease treatment.

Interactions of three berberine mid-chain fatty acid salts with bovine serum albumin (BSA): Spectroscopic analysis and molecular docking

In this paper, the interaction of three berberine mid-chain fatty acid salts ([BBR][FAs]), viz. berberine caproate ([BBR][CAP]), berberine heptylate ([BBR][HEP]) and berberine octoate ([BBR][OCT]), with bovine serum albumin (BSA) was studied by means of UV-visible absorption spectroscopy, fluorescence spectroscopy, fourier transform infrared spectroscopy (FT-IR) and molecular docking techniques. Fluorescence experiments revealed that three berberine salts quench the fluorescence of BSA by static quenching mechanism resulted from a stable [BBR][FAs]-BSA complex formation. The stoichiometric numbers of [BBR][FAs]-BSA complexes were found to be 1:1. Synchronous and three-dimensional fluorescence spectra as well as FT-IR demonstrated that the binding of [BBR][FAs] altered the microenvironment and conformation of BSA. The binding average distance from [BBR][FAs] to BSA (3.2-3.5 nm) was determined according to Förster energy transfer theory. Site probe investigation showed that [BBR][FAs] bound to BSA active site I (sub-domain IIA). The binding promotes the esterase-like activity of BSA. The molecular docking results confirmed the fluorescence competition findings and provided the type of binding forces. Furthermore, the relationship between the anionic chain length of [BBR][FAs] and the interaction was explored, and the positive correlation was found.

Mirror-Image Human Serum Albumin Domain III as a Tool for Analyzing Site II-Dependent Molecular Recognition

Human serum albumin (HSA) as a drug carrier can significantly improve the pharmacokinetic profiles of short-lived therapeutics. Conjugation of albumin-binding moieties (ABMs) to therapeutic agents may prolong their serum half-life by promoting their association with endogenous HSA. To discover a new molecular class of ABMs from mirror-image chemical space, a preparation protocol for bioactive HSA domain III and its d-enantiomer (d-HSA domain III) was established. Structural and functional analyses suggested that the synthetic protein enantiomers exhibited mirror-image structures and stereoselective neonatal fragement crystallizable receptor (FcRn) recognition. Additionally, the ligand-binding properties of synthetic l-HSA domain III were comparable with those of site II in native HSA, as confirmed using site II-selective fluorescent probes and an esterase substrate. Synthetic d-HSA domain III is an attractive tool for analyzing the site II-dependent molecular recognition properties of HSA.

The weakened physiological functions of human serum albumin in presence of polystyrene nanoplastics

Due to the widespread presence of nanoplastics (NPs) in daily essentials and drinking water, the potential adverse effects of NPs on human health have become a global concern. Human serum albumin (HSA), the most abundant and multi-functional protein in plasma, has been chosen to understand the biological effects of NPs after entering the blood. The esterase activity and the transport of bisphenol A in the presence of polystyrene nanoplastics (PSNPs) under physiological conditions (pH 4.0 and 7.4) have been investigated to evaluate the possible biological effects. The interactions between PSNPs and HSA have also been systematically studied by multispectral methods and dynamic light scattering techniques. The esterase activity of HSA presented a decreased trend with increasing PSNPs; conversely, higher permeabilities are accompanied by higher amounts of PSNPs. Compared with the unchanged hydrodynamic diameter and weaker interactions at pH 7.4, stronger binding between HSA and PSNPs at pH 4.0 led to a significant increase in the particle size of the PSNPs-HSA complex. The quenching mechanism belonged to the static quenching type. The electrostatic force is proposed to be the dominant factor for PSNPs binding to HSA. The work provides some information about the toxicity of NPs when exposed to humans.

Quantitative Determination of (R)-3-Hydroxybutyl (R)-3-Hydroxybutyrate (Ketone Ester) and Its Metabolites Beta-hydroxybutyrate, 1-3-Butanediol, and Acetoacetate in Human Plasma Using LC-MS

Ketone ester ((R)-3-hydroxybutyl (R)-3-hydroxybutyrate) has gained popularity as an exogenous means to achieve ketosis. Regarding its potential as a therapeutic prodrug, it will be necessary to study its pharmacokinetic profile and its proximal metabolites (beta-hydroxybutyrate, 1,3-butanediol, and acetoacetate) in humans. Here we develop and validate two LC-MS methods for quantifying KE and its metabolites in human plasma. The first assay uses a C18 column to quantitate ketone ester, beta-hydroxybutyrate, and 1,3-butanediol, and the second assay uses a hydrophilic interaction liquid chromatography (HILIC) column for the quantitation of acetoacetate. The method was partially validated for intra- and inter-day accuracy and precision based on the ICH M10 guidelines. For both the assays, the intra- and inter-run accuracy was ±15% of the nominal concentration, and the precision (%CV) was <15% for all 4 molecules being quantified. The matrix effect for all molecules was evaluated and ranged from -62.1 to 44.4% (combined for all molecules), while the extraction recovery ranged from 65.1 to 119% (combined for all molecules). Furthermore, the metabolism of ketone ester in human plasma and human serum albumin was studied using the method. Non-saturable metabolism of ketone ester was seen in human plasma at concentrations as high as 5 mM, and human serum albumin contributed to the metabolism of ketone ester. Together, these assays can be used to track the entire kinetics of ketone ester and its proximal metabolites. The reverse-phase method was used to study the metabolic profile of KE in human plasma and the plasma protein binding of 1,3-BD.

Albumin Is a Component of the Esterase Status of Human Blood Plasma

The esterase status of blood plasma can claim to be one of the universal markers of various diseases; therefore, it deserves attention when searching for markers of the severity of COVID-19 and other infectious and non-infectious pathologies. When analyzing the esterase status of blood plasma, the esterase activity of serum albumin, which is the major protein in the blood of mammals, should not be ignored. The purpose of this study is to expand understanding of the esterase status of blood plasma and to evaluate the relationship of the esterase status, which includes information on the amount and enzymatic activity of human serum albumin (HSA), with other biochemical parameters of human blood, using the example of surviving and deceased patients with confirmed COVID-19. In experiments in vitro and in silico, the activity of human plasma and pure HSA towards various substrates was studied, and the effect of various inhibitors on this activity was tested. Then, a comparative analysis of the esterase status and a number of basic biochemical parameters of the blood plasma of healthy subjects and patients with confirmed COVID-19 was performed. Statistically significant differences have been found in esterase status and biochemical indices (including albumin levels) between healthy subjects and patients with COVID-19, as well as between surviving and deceased patients. Additional evidence has been obtained for the importance of albumin as a diagnostic marker. Of particular interest is a new index, [Urea] × [MDA] × 1000/(BChEb × [ALB]), which in the group of deceased patients was 10 times higher than in the group of survivors and 26 times higher than the value in the group of apparently healthy elderly subjects.

Computational study to find the goat serum albumin (GSA) binding site as A-esterase

A-esterases are a classical term applied to enzymatic activity of the proteins by a mechanism not involving intermediate covalent phosphorylation, but requiring a divalent cation cofactor. Recently, a copper-dependent A-esterase activity has been identified in goat serum albumin (GSA) on the organophosphorus insecticide trichloronate. This hydrolysis was identified ex vivo with spectrophotometry and chromatography techniques. Albumin mechanism of action and catalytic site as Cu²⁺-dependent A-esterase are still unknown. Therefore, to know the copper bind to albumin is relevant. N-terminal sequence has been reported as the high affinity site for this cation, due to the histidine in position 3. The aim of this work In Silico is to explore how occurs this metallic binding and active the esterase catalytic function. The GSA crystallized structure (PDB: 5ORI) was chosen for molecular docking and dynamics. A site-directed docking, for N-terminal site and a blind docking was done with trichloronate as ligand. Root-mean-square deviation and frequency plot was calculated to find the most frequent predicted structure and visualize the amino acids involved in binding site. The affinity energy in the blind docking (-5.804 kcal/mol) is almost twice lower than site-directed docking (-3.816 kcal/mol) and N-terminal amino acids do not appear in the most repeated structure binding site, suggesting that the protein has a site with higher affinity to the trichloronate ligand. His145 could be involved in the binding site as has been reported in previous studies.

Deacetylation of K481 and K484 on Penaeid Shrimp Hemocyanin Is Critical for Antibacterial Activity

Although invertebrates' innate immunity relies on several immune-like molecules, the diversity of these molecules and their immune response mechanisms are not well understood. Here, we show that Penaeus vannamei hemocyanin (PvHMC) undergoes specific deacetylation under Vibrio parahaemolyticus and LPS challenge. In vitro deacetylation of PvHMC increases its binding capacity with LPS and antibacterial activity against Gram-negative bacteria. Lysine residues K481 and K484 on the Ig-like domain of PvHMC are the main acetylation sites modulated by the acetyltransferase TIP60 and deacetylase HDAC3. Deacetylation of PvHMC on K481 and K484 allows PvHMC to form a positively charged binding pocket that interacts directly with LPS, whereas acetylation abrogates the positive charge to decrease PvHMC-LPS attraction. Besides, V. parahaemolyticus and LPS challenge increases the expression of Pvhdac3 to induce PvHMC deacetylation. This work indicates that, during bacterial infections, deacetylation of hemocyanin is crucial for binding with LPS to clear Gram-negative bacteria in crustaceans.

Spontaneous desorption of protein from self-assembled monolayer (SAM)-coated gold nanoparticles induced by high temperature

The nonspecific binding of proteins with nanomaterials (NMs) is a dynamic reversible process including both protein adsorption and desorption parts, which is crucial for controlled release of protein drug loaded by nanocarriers. The nonspecific binding of proteins is susceptible to high temperature, whereas its underlying mechanism still remains elusive. Here, the binding behavior of human serum albumin (HSA) with an amino-terminated self-assembled monolayer (SAM)-coated gold (111) surface was investigated by using molecular dynamics (MD) simulations. HSA binds to the SAM surface through salt bridges at 300 K. As the temperature increases to 350 K, HSA maintains its native structure, while the salt bridges largely diminish owing to the considerable lateral diffusion of HSA on the SAM. Moreover, the interfacial water located between HSA and the SAM gets increased and prevents the reformation of the salt bridges of HSA with the SAM, which reduces the binding affinity of HSA. And HSA eventually desorbs from the SAM. The depiction of thermally induced spontaneous protein desorption enriches our understanding of reversible binding behavior of protein with NMs, and may provide new insights into the controlled release of protein drugs delivered by using nanocarriers under the regulation of high temperature.

Fluorimetric method for specific detection of human serum albumin in urine using its pseudoesterase property

Detection of microalbuminuria is an analytical challenge. There are dye-based methods and immunochemical methods. However, these methods are less specific and sensitive respectively. So, people are trying new approaches for microalbuminuria detection. In this context, we have developed a fluorescent spectroscopic method to detect human serum albumin using its pseudoesterase property. Recently, we had discovered that neostigmine does not inhibit Human serum albumin pseudoesterase activity. Using such a phenomenon, we have devised a specific fluorimetric detection method of HSA using 2NA as a substrate for the pseudoesterase activity. The developed method can sense as low as 0.1 μM of HSA in the urine matrix without dye or antibody. We have proposed a scheme of automation of the proposed method.

Esterase Activity of Serum Albumin Studied by 1H NMR Spectroscopy and Molecular Modelling

Serum albumin possesses esterase and pseudo-esterase activities towards a number of endogenous and exogenous substrates, but the mechanism of interaction of various esters and other compounds with albumin is still unclear. In the present study, proton nuclear magnetic resonance (1H NMR) has been applied to the study of true esterase activity of albumin, using the example of bovine serum albumin (BSA) and p-nitrophenyl acetate (NPA). The site of BSA esterase activity was then determined using molecular modelling methods. According to the data obtained, the accumulation of acetate in the presence of BSA in the reaction mixture is much more intense as compared with the spontaneous hydrolysis of NPA, which indicates true esterase activity of albumin towards NPA. Similar results were obtained for p-nitophenyl propionate (NPP) as substrate. The rate of acetate and propionate release confirms the assumption that there is a site of true esterase activity in the albumin molecule, which is different from the site of the pseudo-esterase activity Sudlow II. The results of molecular modelling of BSA and NPA interaction make it possible to postulate that Sudlow site I is the site of true esterase activity of albumin.

Serum Albumin in Health and Disease: Esterase, Antioxidant, Transporting and Signaling Properties

Being one of the main proteins in the human body and many animal species, albumin plays a decisive role in the transport of various ions-electrically neutral and charged molecules-and in maintaining the colloidal osmotic pressure of the blood. Albumin is able to bind to almost all known drugs, as well as many nutraceuticals and toxic substances, largely determining their pharmaco- and toxicokinetics. Albumin of humans and respective representatives in cattle and rodents have their own structural features that determine species differences in functional properties. However, albumin is not only passive, but also an active participant of pharmacokinetic and toxicokinetic processes, possessing a number of enzymatic activities. Numerous experiments have shown esterase or pseudoesterase activity of albumin towards a number of endogeneous and exogeneous esters. Due to the free thiol group of Cys34, albumin can serve as a trap for reactive oxygen and nitrogen species, thus participating in redox processes. Glycated albumin makes a significant contribution to the pathogenesis of diabetes and other diseases. The interaction of albumin with blood cells, blood vessels and tissue cells outside the vascular bed is of great importance. Interactions with endothelial glycocalyx and vascular endothelial cells largely determine the integrative role of albumin. This review considers the esterase, antioxidant, transporting and signaling properties of albumin, as well as its structural and functional modifications and their significance in the pathogenesis of certain diseases.

Serum Albumin: A Multifaced Enzyme

Human serum albumin (HSA) is the most abundant protein in plasma, contributing actively to oncotic pressure maintenance and fluid distribution between body compartments. HSA acts as the main carrier of fatty acids, recognizes metal ions, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays esterase, enolase, glucuronidase, and peroxidase (pseudo)-enzymatic activities. HSA-based catalysis is physiologically relevant, affecting the metabolism of endogenous and exogenous compounds including proteins, lipids, cholesterol, reactive oxygen species (ROS), and drugs. Catalytic properties of HSA are modulated by allosteric effectors, competitive inhibitors, chemical modifications, pathological conditions, and aging. HSA displays anti-oxidant properties and is critical for plasma detoxification from toxic agents and for pro-drugs activation. The enzymatic properties of HSA can be also exploited by chemical industries as a scaffold to produce libraries of catalysts with improved proficiency and stereoselectivity for water decontamination from poisonous agents and environmental contaminants, in the so called “green chemistry” field. Here, an overview of the intrinsic and metal dependent (pseudo-)enzymatic properties of HSA is reported to highlight the roles played by this multifaced protein.

Prediction of Human Pharmacokinetic Profiles of the Antituberculosis Drug Delamanid from Nonclinical Data: Potential Therapeutic Value against Extrapulmonary Tuberculosis

Delamanid has been studied extensively and approved for the treatment of pulmonary multidrug-resistant tuberculosis; however, its potential in the treatment of extrapulmonary tuberculosis remains unknown. We previously reported that, in rats, delamanid was broadly distributed to various tissues in addition to the lungs. In this study, we simulated human plasma concentration-time courses (pharmacokinetic profile) of delamanid, which has a unique property of metabolism by albumin, using two different approaches (steady-state concentration of plasma-mean residence time [C_ss-MRT] and physiologically based pharmacokinetic [PBPK] modeling). In C_ss-MRT, allometric scaling predicted the distribution volume at steady state based on data from mice, rats, and dogs. Total clearance was predicted by in vitro-in vivo extrapolation using a scaled albumin amount. A simulated human pharmacokinetic profile using a combination of human-predicted C_ss and MRT was almost identical to the observed profile after single oral administration, which suggests that the pharmacokinetic profile of delamanid could be predicted by allometric scaling from these animals and metabolic capacity in vitro. The PBPK model was constructed on the assumption that delamanid was metabolized by albumin in circulating plasma and tissues, to which the simulated pharmacokinetic profile was consistent. Moreover, the PBPK modeling approach demonstrated that the simulated concentrations of delamanid at steady state in the lung, brain, liver, and heart were higher than the in vivo effective concentration for Mycobacterium tuberculosis. These results indicate that delamanid may achieve similar concentrations in various organs to that of the lung and may have the potential to treat extrapulmonary tuberculosis.

Cu2+-dependent stereoselective hydrolysis of a chiral organophosphonothioate insecticide for domestic mammals' sera and its albumins

Acute toxicity of organophosphate (OPs) pesticides is a public health problem. The adverse effects are associated with the inhibition and aging of nervous system B-esterases such as acetyl cholinesterase (AChE) and neuropathic target esterase (NTE). Treatment based on A-esterases such as mammal serum paraoxonase-1 has been suggested. This ex vivo study shows the Cu²⁺-dependent hydrolysis of trichloronate (TCN), a racemic organophosphonothioate insecticide, in human and domestic mammal serum (dog, goat, pig, sheep and cow). Ca²⁺-dependent (2.5 mM) or EDTA-resistant (5 mM) activity (1-6%) was not significant (p>0.05) in all samples, except goat serum and its albumin, which showed higher levels of TCN hydrolysis (38-58%) than other mammals with 100 and 300 μM copper sulfate at physiological conditions for 60 min. Goat serum albumin (GSA) showed significant (p˂0.05) stereoselective hydrolysis (+)-TCN ˃ (-)-TCN (45% versus 33%). This suggests that GSA is the protein responsible for Cu²⁺-dependent TCNase activity in goat serum. This is the first report on Cu²⁺-dependent A-esterase activity in mammalian tissues. This goat serum cuproprotein could be considered as an alternative in future biotechnological applications including enantiomeric synthesis, bioremediation and antidotal treatment of organophosphonothioate pesticide poisoning.

Aryl N-[ω-(6-Fluoroindol-1-yl)alkyl]carbamates as Inhibitors of Fatty Acid Amide Hydrolase, Monoacylglycerol Lipase, and Butyrylcholinesterase: Structure-Activity Relationships and Hydrolytic Stability

A series of aryl N-[ω-(6-fluoroindol-1-yl)alkyl]carbamates with alkyl spacers of varying lengths between the indole and the carbamate group and with differently substituted aryl moieties at the carbamate oxygen were synthesized and tested for inhibition of the pharmacologically interesting serine hydrolases fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), butyrylcholinesterase (BuChE), and acetylcholinesterase (AChE). Furthermore, the chemical stability in an aqueous solution and the metabolic stability toward esterases in porcine liver homogenate and porcine blood plasma were determined. While most of the synthesized derivatives were potent inhibitors of FAAH, a considerable inhibition of MAGL and BuChE was elicited only by compounds with a high carbamate reactivity, as evidenced by a significant hydrolysis of these compounds in an aqueous solution. However, the high inhibitory potency of some compounds toward MAGL and BuChE, especially that of the ortho-carboxyphenyl derivative 37, could not be explained by chemical reactivity alone. Several of the carbamates studied possessed varying degrees of stability toward esterases from liver and blood plasma. In some cases, marked inactivation by the pseudo-esterase activity of plasma albumin was observed. Mass spectrometric studies showed that such carbamates formed covalent bonds with albumin at several sites.

Pseudosterase activity-based specific detection of human serum albumin on gel

Human serum albumin (HSA) has pseudoesterase activity. So far on gel specific detection of such property of HSA is never reported. Moreover, protein binding dyes are non-specific for albumin. However, many of such dyes are used for HSA detection. So, dye-based albumin detection on the gel is expected to generate false-positive results for HSA. In this context, we have discovered that Fast Blue BB (FBBB, 0.12%) stains specifically HSA pseudoesterase activity with 2 Naphthyl acetate (2NA) as an ester substrate. Further, neostigmine has not inhibited the pseudoesterase activity associated with HSA. Neostigmine is a known inhibitor of many true esterases like acetylcholinesterase. So, neostigmine addition offers specificity to the method developed for staining of HSA. Additionally, 2NA stains HSA better than bovine serum albumin (BSA). Exploring all these novel findings, we have devised a simple method of HSA detection on the gel, accurately where other esterases are not detected. To the best of our knowledge, our method is the first to detect HSA pseudoesterase activity specifically on gel without getting interfered by any other esterase activity. The method detects HSA better than BSA. We feel that this method will go a long way for the specific detection of HSA on the gel. It is also relevant for understanding the purity of donor human milk matrix and pharmaceutical preparation of HSA. Our method can detect 7 μM of added HSA in human urine. Therefore, our method can be proceeded further for microalbuminuria detection in days to come.

Super Secondary Structures of Proteins with Post-Translational Modifications in Colon Cancer

New advances in protein post-translational modifications (PTMs) have revealed a complex layer of regulatory mechanisms through which PTMs control cell signaling and metabolic pathways, contributing to the diverse metabolic phenotypes found in cancer. Using conformational templates and the three-dimensional (3D) environment investigation of proteins in patients with colorectal cancer, it was demonstrated that most PTMs (phosphorylation, acetylation, and ubiquitination) are localized in the supersecondary structures (helical pairs). We showed that such helical pairs are represented on the outer surface of protein molecules and characterized by a largely accessible area for the surrounding solvent. Most promising and meaningful modifications were observed on the surface of vitamin D-binding protein (VDBP), complement C4-A (CO4A), X-ray repair cross-complementing protein 6 (XRCC6), Plasma protease C1 inhibitor (IC1), and albumin (ALBU), which are related to colorectal cancer developing. Based on the presented data, we propose the impact of the observed modifications in immune response, inflammatory reaction, regulation of cell migration, and promotion of tumor growth. Here, we suggest a computational approach in which high-throughput analysis for identification and characterization of PTM signature, associated with cancer metabolic reprograming, can be improved to prognostic value and bring a new strategy to the targeted therapy.

Mass Spectrometry-Based Protein Footprinting for Higher-Order Structure Analysis: Fundamentals and Applications

Proteins adopt different higher-order structures (HOS) to enable their unique biological functions. Understanding the complexities of protein higher-order structures and dynamics requires integrated approaches, where mass spectrometry (MS) is now positioned to play a key role. One of those approaches is protein footprinting. Although the initial demonstration of footprinting was for the HOS determination of protein/nucleic acid binding, the concept was later adapted to MS-based protein HOS analysis, through which different covalent labeling approaches "mark" the solvent accessible surface area (SASA) of proteins to reflect protein HOS. Hydrogen-deuterium exchange (HDX), where deuterium in D2O replaces hydrogen of the backbone amides, is the most common example of footprinting. Its advantage is that the footprint reflects SASA and hydrogen bonding, whereas one drawback is the labeling is reversible. Another example of footprinting is slow irreversible labeling of functional groups on amino acid side chains by targeted reagents with high specificity, probing structural changes at selected sites. A third footprinting approach is by reactions with fast, irreversible labeling species that are highly reactive and footprint broadly several amino acid residue side chains on the time scale of submilliseconds. All of these covalent labeling approaches combine to constitute a problem-solving toolbox that enables mass spectrometry as a valuable tool for HOS elucidation. As there has been a growing need for MS-based protein footprinting in both academia and industry owing to its high throughput capability, prompt availability, and high spatial resolution, we present a summary of the history, descriptions, principles, mechanisms, and applications of these covalent labeling approaches. Moreover, their applications are highlighted according to the biological questions they can answer. This review is intended as a tutorial for MS-based protein HOS elucidation and as a reference for investigators seeking a MS-based tool to address structural questions in protein science.

Study of protective properties of butyrylcholinesterase in acute anticholinesterase poisoning on BChE-KO and BALB/c mice

Introduction: The article presents the results of studying the protective properties of recombinant human butyrylcholinesterase (rhBChE) in a model of acute anticholinesterase poisoning in mice knocked out for the BChE gene. Balb/c inbred mice were also used to demonstrate the important role of BChE.

Materials and methods: In the study, BChE-ko and Balb/c mice were used. An organophosphorus compound (OPC) paraoxon was used as a toxic agent causing acute anticholinesterase poisoning. rhBChE was used as an antidote for OPC poisoning. To obtain rhBChE, an expression system based on CHO cell lines was chosen. In order to suppress BChE in Balb/c mice, a carboxyl esterase blocker cresylbenzodioxaphosphorin oxide (CBDP) was used. Two parameters were used to study the recovery after toxicity modeling: the end time of the animal tremor and the distance covered in open-field for 3 minutes.

Results and discussion: The acute poisoning model using the CBDP blocker showed that the sensitivity of Balb/c mice increased significantly. The use of rhBChE against the background of CBDP allowed achieving 100% survival of animals with the minimum lethal dose of paraoxon. Knockout mice are expected to be more sensitive to the toxin, and the use of a biological trap in the form of rhBChE made it possible for 70% of the animals to survive with the minimum lethal dose of paraoxon. Besides, the use of rhBChE facilitated reducing the recovery time after OPC poisoning.

Conclusion: The results of the study showed that the use of rhBChE as a protective agent in acute OPC poisoning significantly increased the survival of the animals and reduced the clinical manifestations of poisoning.

Sequestration of Cetyltrimethylammonium Bromide on Gold Nanorods by Human Serum Albumin Causes Its Conformation Change

Serum albumin could potentially be exploited to form a protein corona on gold nanorods (AuNRs) for drug delivery because of its endogenous functionality as a small molecule carrier. However, the cetyltrimethylammonium bromide (CTAB) surfactant, which is a synthesis byproduct passivating AuNRs to confer colloidal stability, could also cause its conformational change upon interaction with serum albumin during the process of corona formation, thus altering its biological functions. Unfortunately, a clear understanding of how exactly human serum albumin (HSA) would change its conformation as it interacts with AuNR-CTAB is presently lacking. Here, we made use of coarse-grain molecular dynamics (CGMD) simulation to elucidate the interaction between HSA and AuNR-CTAB leading to its widely reported conformational change. We showed that HSA could sequester CTAB from the surface of AuNRs and form HSA-CTAB complexes, which could also interact with other adjacent complexes through "cross-linking" by the clusters of CTAB. Such a HSA-CTAB complex resulted in the observed conformational change of HSA, which we verified empirically with an esterase activity assay and by analyzing the root-mean-square-deviation of the HSA molecules from CGMD. The conformational change of HSA was not observed in AuNRs passivated with other negatively or positively charged surface ligands such as polystyrene sulfonate and polydiallyldimethylammonium chloride. Therefore, our study revealed that the conformational change experienced by HSA may not necessarily be attributed to protein unfolding on the surface of the AuNR due to charge interactions but rather to the instability of the surface ligands on the AuNRs which allows them to be sequestered by HSA to form HSA-CTAB complexes.

Photobinding of Triflusal to Human Serum Albumin Investigated by Fluorescence, Proteomic Analysis, and Computational Studies

Triflusal is a platelet antiaggregant employed for the treatment and prevention of thromboembolic diseases. After administration, it is biotransformed into its active metabolite, the 2-hydroxy-4-trifluoromethylbenzoic acid (HTB). We present here an investigation on HTB photobinding to human serum albumin (HSA), the most abundant protein in plasma, using an approach that combines fluorescence, MS/MS, and peptide fingerprint analysis as well as theoretical calculations (docking and molecular dynamics simulation studies). The proteomic analysis of HTB/HSA photolysates shows that HTB addition takes place at the ε-amino groups of the Lys137, Lys199, Lys205, Lys351, Lys432, Lys525, Lys541 and Lys545 residues and involves replacement of the trifluoromethyl moiety of HTB with a new amide function. Only Lys199 is located in an internal pocket of the protein, and the remaining modified residues are placed in the external part. Docking and molecular dynamic simulation studies reveal that HTB supramolecular binding to HSA occurs in the "V-cleft" region and that the process is assisted by the presence of Glu/Asp residues in the neighborhood of the external Lys, in agreement with the experimentally observed modifications. In principle, photobinding can occur with other trifluoroaromatic compounds and may be responsible for the appearance of undesired photoallergic side effects.

Interspecies differences in stability kinetics and plasma esterases involved in hydrolytic activation of curcumin diethyl disuccinate, a prodrug of curcumin

The investigation of in vitro plasma metabolism of ester prodrugs is an important part of in vitro ADME assays during preclinical drug development. Here, we show that the in vitro metabolism including plasma stability and metabolizing enzymes of curcumin diethyl disuccinate (CDD), an ester prodrug of curcumin, in dog and human plasma are similar but markedly different from those in rat plasma. HPLC and nonlinear regression analyses indicated that the hydrolysis of CDD in plasma followed a consecutive pseudo-first order reaction. The rapid hydrolytic cleavage of CDD in rat, dog, and human plasma was accelerated by plasma esterases in the following order: rat ≫ human > dog. LC-Q-TOF/MS analysis showed that the cleavage of ester bonds of CDD is preferential at the phenolic ester. Monoethylsuccinyl curcumin is the only intermediate metabolite found in plasma metabolism of CDD in all tested species. Further investigation using different esterase inhibitors revealed that carboxylesterase is the major enzyme involved in the hydrolysis of CDD in rats while multiple plasma esterases play a role in dogs and humans. Thus, the difference in the hydrolysis rates and the metabolizing enzymes of CDD metabolism in rat, dog and human plasma observed here is of benefit to further in vivo studies and provides a rationale for designing ester prodrugs of CUR with esterase-specific bioactivation.

Identification of Carboxylesterase, Butyrylcholinesterase, Acetylcholinesterase, Paraoxonase, and Albumin Pseudoesterase in Guinea Pig Plasma through Nondenaturing Gel Electrophoresis

Drugs to protect against nerve agent toxicity are tested in animals. The current preferred small animal model is guinea pigs because their plasma bioscavenging capacity resembles that of NHP. We stained nondenaturing polyacrylamide slab gels with a variety of substrates, inhibitors, and antibodies to identify the esterases in heparinized guinea pig plasma. An intense band of carboxylesterase activity migrated behind albumin. Minor carboxylesterase bands were revealed after background activity from paraoxonase was inhibited by using EDTA. The major butyrylcholinesterase band was a disulfide-linked dimer. Incubation with the antihuman butyrylcholinesterase antibody B2 18-5 shifted the butyrylcholinesterase dimer band to slower migrating complexes. Carboxylesterases were distinguished from butyrylcholinesterase by their sensitivity to inhibition by bis-p-nitrophenyl phosphate. Acetylcholinesterase tetramers formed a complex with the antihuman acetylcholinesterase antibody HR2. Organophosphorus toxicants including cresyl saligenin phosphate, dichlorvos, and chlorpyrifos oxon irreversibly inhibited the serine esterases but not paraoxonase. Albumin pseudoesterase activity was seen in gels stained with α- or β-naphthyl acetate and fast blue RR. We conclude that guinea pig plasma has 2 types of carboxylesterase, butyrylcholinesterase dimers and 5 minor butyrylcholinesterase forms, a small amount of acetylcholinesterase tetramers, paraoxonase, and albumin pseudoesterase activity. A knockout mouse with no carboxylesterase activity in plasma is available and may prove to be a better model for studies of nerve agent toxicology than guinea pigs.

Pseudoesterase activity of albumin: A probable determinant of cholesterol biosynthesis

The association between hypoalbuminemia and coronary artery disease is known from some time. However, the reason as to how such phenomenon is correlated remains unknown. We have observed from published scientific literature that HSA has the potential to control cholesterol biosynthesis due to its pseudoesterase activity. In-silico observations have supported our view since acetyl coA, the precursor molecule of cholesterol biosynthesis is shown to bind with Tyr 411 of HSA. Incidentally, Tyr411 is a critical moiety for pseudoesterase activity of albumin. With this frame of reference in mind we hypothesize that pseudoesterase activity of HSA is an important determinant of lipid metabolism including cholesterol biosynthesis. Therefore, albumin has the potential to influence the atherosclerotic state important for pathogenesis of coronary artery diseases.

Understanding the fate of human serum albumin upon interaction with edifenphos: Biophysical and biochemical approaches

Edifenphos (EDF), an important organophosphate fungicide used in agriculture, is a great threat to human health and environment. To assess the toxicity of EDF at the level of protein molecule, the effect of EDF on human serum albumin (HSA) was investigated by biophysical and biochemical approaches. EDF-HSA complex is formed as a result of static quenching as revealed by the intrinsic fluorescence analysis. Thermodynamic analysis of the binding data suggests involvement of hydrophobic interactions in EDF-HSA complex formation, which is in line with molecular docking results. Moreover, thermodynamic parameters of binding between EDF and HSA suggest entropy-driven spontaneous interaction, presumably dominated by hydrophobic forces. Further, binding site of EDF seems to have been located within sub-domain IIA of HSA. EDF binding to HSA decreases its alpha helical content as analyzed by CD spectra. Marked micro-environmental changes around tryptophan/tyrosine residues in HSA upon EDF binding were recorded via three-dimensional fluorescence spectroscopy. Substantial release of protein carbonyl from HSA as a result of EDF treatment suggested involvement of ROS in EDF induced protein damage. This work is expected to provide some leads toward EDF induced toxicity in humans and would be helpful in reinforcing the check on food safety.

Zinc oxide nanoparticles provide anti-cholera activity by disrupting the interaction of cholera toxin with the human GM1 receptor

Vibrio cholerae causes cholera and is the leading cause of diarrhea in developing countries, highlighting the need for the development of new treatment strategies to combat this disease agent. While exploring the possibility of using zinc oxide (ZnO) nanoparticles (NPs) in cholera treatment, we previously found that ZnO NPs reduce fluid accumulation in mouse ileum induced by the cholera toxin (CT) protein. To uncover the mechanism of action of ZnO NPs on CT activity, here we used classical (O395) and El Tor (C6706) V. cholerae biotypes in growth and biochemical assays. We found that a ZnO NP concentration of 10 μg/ml did not affect the growth rates of these two strains, nor did we observe that ZnO NPs reduce the expression levels of CT mRNA and protein. It was observed that ZnO NPs form a complex with CT, appear to disrupt the CT secondary structure, and block its interaction with the GM1 ganglioside receptor in the outer leaflet of the plasma membrane in intestinal (HT-29) cells and thereby reduce CT uptake into the cells. In the range of 2.5-10 μg/ml, ZnO NPs exhibited no cytotoxicity on kidney (HEK293) and HT-29 cells. We conclude that ZnO NPs prevent the first step in the translocation of cholera toxin into intestinal epithelial cells without exerting measurable toxic effects on HEK293 and HT-29 cells.

Serum Albumin Binding and Esterase Activity: Mechanistic Interactions with Organophosphates

The albumin molecule, in contrast to many other plasma proteins, is not covered with a carbohydrate moiety and can bind and transport various molecules of endogenous and exogenous origin. The enzymatic activity of albumin, the existence of which many scientists perceive skeptically, is much less studied. In toxicology, understanding the mechanistic interactions of organophosphates with albumin is a special problem, and its solution could help in the development of new types of antidotes. In the present work, the history of the issue is briefly examined, then our in silico data on the interaction of human serum albumin with soman, as well as comparative in silico data of human and bovine serum albumin activities in relation to paraoxon, are presented. Information is given on the substrate specificity of albumin and we consider the possibility of its affiliation to certain classes in the nomenclature of enzymes.