Alterations Of Protein Secondary Structure Research Articles

Ultrasound-assisted improvement of thawing quality of Tibetan pork by inhibiting oxidation

The challenge of meat quality degradation due to transportation difficulties in high-altitude plateaus underscores the importance of an efficient thawing process for Tibetan pork to ensure its quality. This study compared four thawing methods ultrasound thawing (UT), refrigerator thawing (RT), hydrostatic thawing (HT), and microwave thawing (MT) to assess their impact on the quality of Tibetan pork, focusing on thawing loss, tenderness, color variation, and alterations in protein secondary structure and moisture content. Additionally, the study examined the impact of thawing on the metabolites of Tibetan pork using metabolomics techniques. The results indicated that UT yielded the highest quality samples. UT significantly accelerated the thawing rate and had minimal impact on tenderness compared to traditional thawing methods. Moreover, protein and lipid oxidation levels were reduced by UT treatment. Furthermore, it enhanced the binding capacity of protein and water molecules, reduced drip loss, and maintained meat color stability. What’s more, amino acid metabolites such as l-glutamic acid, l-proline, oxidized glutathione, and 1-methylhistidine played a significant role in thawing oxidation in Tibetan pork, exhibiting a positive correlation with protein oxidation. UT resulted in a notable decrease in the levels of hypoxanthine and 2-aminomethylpyrimidine, contributing to the reduction of bitterness in the thawed meat and consequently enhancing the freshness of Tibetan pork. This study offers novel insights into understanding the biological changes occurring during the thawing process, while also furnishing a theoretical framework and technical assistance to improve the quality of Tibetan pork and propel advancements in food processing technology.

Effect of protein structure changes during different power ultrasound thawing on emulsification properties of common carp (Cyprinus carpio) myofibrillar protein

The impact of ultrasound thawing (UT) at different power (0 W, 100 W/0.132 W·cm−2, 300 W/1.077 W·cm−2, and 500 W/1.997 W·cm−2, namely WT, UT-100, UT-300, and UT-500) on protein structure, aggregation, and emulsifying properties of common carp (Cyprinus carpio) myofibrillar protein were investigated in the present study. The result showed that the reactive sulfhydryl content, total sulfhydryl content, protein solubility, and absolute potential of UT-300 samples were obviously higher than those of other thawed samples, while the turbidity of UT-300 samples was lower (P < 0.05), which indicated that proper UT power was beneficial to inhibit protein aggregation caused by thawing, while too low (100 W) or too high (500 W) ultrasonic power had poor effect. The Ca2+-ATPase activity and thermal stability of UT-300 samples were much higher than those of other thawed samples (P < 0.05), indicating that UT-300 inhibited myosin denaturation and thermal stability reduction of thawed products. The α-helix content of UT-300 samples was higher than that of other thawed samples, while the β-sheet content was significantly lower than that of other thawed samples (P < 0.05). The fluorescence intensity of UT-300 samples was higher than that of other thawed samples, and the λmax of UT-300 samples and UT-100 samples were lower than that of other thawed samples, which indicated that UT-300 could effectively inhibit the alteration of protein secondary structure and tertiary structure during thawing. The emulsifying activity of UT-300 samples was significantly higher than that of WT samples, and the droplet diameter of UT-300 samples was also lower than that of WT samples (P < 0.05), which indicated that UT-300 inhibited the decrease of emulsifying property during thawing. Overall, moderate ultrasonic power (300 W) could effectively inhibit the protein aggregation and structural changes during thawing, led to the decrease of emulsifying activity.

Comparative Study of Time-Dependent Aluminum Exposure and Post-Exposure Recovery Shows Better Improvement in Synaptic Changes andNeuronal Pathology in Rat Brain After Short-Term Exposure.

Aluminum is a ubiquitous metal that causes multiple brain pathologies such as, cognitive dysfunction and Alzheimer's disease like symptoms. Exposure to aluminum through drinking water is responsible for hampering learning and memory. This study aimed to compare (1) the time-dependent effect of aluminum exposure (keeping total exposure of 5850mg/kg same) in two durations, 30 and 45days, and (2) to compare post-exposure self-recovery effect after 20days in both (30 and 45days exposure) groups. Rats were given 130 and 195mg/kg of AlCl3·6H2O for 45 and 30days respectively, to see the time-dependent exposure effect. At the end of exposure, rats were given distilled water and allowed to self-recover for 20days to study the recovery. Expressionlevelsof synaptic genes (Syp, SNAP25, Nrxn1/2, PSD95, Shank1/2, Homer1, CamkIV, Nrg1/2 and Kalrn) were measured using qPCR and compared in the exposure and recovery groups. Cellular morphology of the rat brain cortex and hippocampus was also investigated. Damage in lipid and protein profile was measured by employing FTIR. Results showed downregulation of mRNA expression of synaptic genes, plaques deposition, disorganization in lipid and protein profile by increasing membrane fluidity, and disorder and alteration of protein secondary structure after both exposure periods. However, better improvement/recovery in these parameters were observed in recovery group of 30days aluminum exposure compared to 45days aluminum exposure group. Taken together, these results suggested that short-term exposure resulted in better restoration of lipid and protein profile after time-dependent exposure of aluminum than prolonged exposure.

Denatured Crude Protein Extracts from the Sea Anemone Entacmaea quadricolor as Capping Agents for Silver Nanoclusters

Silver nanoclusters (AgNC) have gained considerable attention for their potential applications. In present work, crude protein extracts from the sea anemone Entacmaea quadricolor subjected to either heat or β-mercaptoethanol denaturation were prepared to investigate the effects of these processes in the formation of AgNC and on its preliminary bioactivity, measured using a hemolysis assay against human erythrocytes. Fourier-transform infrared spectrometry (FTIR) analysis of silver nanoclusters showed no significant alterations in protein secondary structure upon nanocluster formation for all samples. All samples, including the crude protein extracts, were found to be weakly hemolytic at the concentration range tested (0.5-1.0 mg protein/mL). These results imply that E. quadricolor crude protein denaturation prior to use with the reduction of Ag+ has no deleterious effects in functioning as capping agents for the prepared AgNC.

Study on the cytotoxic, antimetastatic and albumin binding properties of the oxidovanadium(IV) chrysin complex. Structural elucidation by computational methodologies

We have previously synthesized and characterized the chrysin coordination complex with the oxidovanadium(IV) cation (VIVO(chrys)2) and characterized in ethanolic solution and in solid state. Because suitable single crystals for X-ray diffraction determinations could not be obtained, in the present work, we elucidate the geometrical parameters of this complex by computational methodologies. The optimization and vibrational investigation were carried out both in ethanolic solution and in gas phase. The computational results support the experimentally proposed geometries of the VIVO(chrys)2 complex, thus leading to the conclusion that the complex exists as conformers with trans-octahedral geometry in ethanolic solution and as conformers with cis-octahedral geometry in the solid state. The complex also exists as conformers with trans-octahedral geometry in aqueous media. The active species formed after dissolution in DMSO showed anticancer and antimetastatic behavior in human lung cell line A549 with moderate binding (Kaca. 105 M−1) to bovine serum albumin (BSA). The interaction through hydrogen bonding and van der Waals forces resulted in a spontaneous process. Site marker competitive experiments showed binding sites for chrysin mainly located in site II (subdomain IIIA) and in site I (subdomain IIIA) for the complex. FT-IR spectral measurements showed evidences of the alterations of protein secondary structure in the presence of chrysin and VIVO(chrys)2.

The effect of atmospheric cold plasma treatment on the antigenic properties of bovine milk casein and whey proteins

Casein, β-lactoglobulin and α-lactalbumin are major milk protein allergens. In the present study, the structural modifications and antigenic response of these bovine milk allergens as induced by non-thermal treatment by atmospheric cold plasma were investigated. Spark discharge (SD) and glow discharge (GD), as previously characterized cold plasma systems, were used for protein treatments. Casein, β-lactoglobulin and α-lactalbumin were analyzed before and after plasma treatment using SDS-PAGE, FTIR, UPLC-MS/MS and ELISA. SDS-PAGE results revealed a reduction in the casein and α-lactalbumin intensity bands after SD or GD treatments; however, the β-lactoglobulin intensity band remained unchanged. FTIR studies revealed alterations in protein secondary structure induced by plasma, particularly contents of β-sheet and β-turn. The UPLC-MS/MS results showed that the amino acid compositions decreased after plasma treatments. ELISA of casein and α-lactalbumin showed a decrease in antigenicity post plasma treatment, whereas ELISA of β-lactoglobulin showed an increase in antigenicity. The study indicates that atmospheric cold plasma can be tailored to mitigate the risk of bovine milk allergens in the dairy processing and ingredients sectors.

Biomolecular study and conjugation of two para-aminobenzoic acid derivatives with serum proteins: drug binding efficacy and protein structural analysis

Two aminobenzoic acid derivatives DAB-0 and DAB-1 showed distinct biological properties on murine bladder cancer (BCa) cell line MB49-I. In contrast to DAB-1, DAB-0 does not possess any anti-inflammatory activity and is less toxic. Furthermore, DAB-0 does not interfere with INFγ-induced STAT1 activation and TNFα-induced IκB phosphorylation, while DAB-1 does. In order to rationalize these results, the binding efficacy of DAB-0 and DAB-1 with serum proteins such a human serum albumin (HSA), bovine serum albumin (BSA) and beta-lactoglobulin (β-LG) was investigated in aqueous solution at physiological pH. Multiple spectroscopic methods and thermodynamic analysis were used to determine the binding efficacy of DAB-0 and DAB-1 with serum proteins. Drug-protein conjugation was observed via through ionic contacts. DAB-1 forms stronger adducts than DAB-0, while β-LG shows more affinity with the order of stability β-LG > BSA > HSA. The stronger complexation of DAB-1 with serum proteins might account for its biological potential and transport in the blood. The binding efficacy ranged from 40 to 60%. Major alterations of protein secondary structures were detected upon drug complexation. Serum proteins are capable of delivering DAB-1 in vitro.Communicated by Ramaswamy H. Sarma

Conjugation of vitamin C with serum proteins: A potential application for vitamin delivery

Vitamin C plays an important role in human health and therefore, the bioavailability and delivery of this micronutrient in solution have been the subject of intensive studies. Serum proteins are known to play an important role as drug delivery tools with important clinical applications. The conjugation of l-ascorbic acid with human serum albumin (HSA), bovine serum albumin (BSA) and beta-lactoglobulin (β-LG) was investigated in aqueous solution at physiological pH. Multiple spectroscopic methods, thermodynamic analysis and modeling were used to determine the binding efficacy of the vitamin C with serum proteins. Acid-protein conjugation occurred via ionic contacts. Acid forms more stable adducts with β-LG with the order of stability β-LG > HSA > BSA. The loading efficacy was 45–60%. Major alterations of protein secondary structures were observed upon acid conjugation. Serum proteins can deliver vitamin C in vitro.

Co-precipitation Synthesis of Near-infrared Iron Oxide Nanocrystals on Magnetically Targeted Imaging and Photothermal Cancer Therapy via Photoablative Protein Denature.

Near-infrared (NIR)-based nanomaterials that provide efficient tumor ablation for cancer therapy have been reported. However, the issues of biocompatibility of metals or ions in inorganic nanoparticles systems such as copper and gold nanoparticles are still a matter of concern. In this study, we developed a facile and ligand-assisted co-precipitation method to synthesize biocompatible iron oxide (IO) nanocrystals with NIR absorption that provided T2-weighted magnetic resonance (MR) images and photothermal ablation characteristics suitable for cancer theranostics. Our results showed that 150-nm particles can be synthesized and optimized by using different amounts of ligand. NIR-IO nanocrystals of this size showed high photothermal conversion efficiency (21.2%) and T2-weighted MR contrast (transverse relaxivity value approximately 141 S-1 mM-1). The NIR-IO nanocrystals showed no cytotoxicity in HT-29 colorectal cancer cells without irradiation, whereas the viability of cells that received NIR-IO nanocrystals decreased significantly after 808-nm laser irradiation. The mechanism of cell death may involve alterations in protein secondary structure and membrane permeability. For in vivo studies, 4-fold enhanced tumor accumulation was significantly observed of NIR-IO nanocrystals with a magnetic field (MF) application, resulting in a 3-fold higher T2-weighted MR signal than that produced by a commercial T2-weighted MR contrast agent (Resovist®) and excellent photothermal efficacy (approximately 53 °C) for cancer treatment. The innovative NIR-IO nanocrystals showed excellent biocompatibility and have great potential as a theranostic agent against cancer.

Conjugation of testo and testo-Pt(II) with serum proteins: Loading efficacy and protein conformation

The potential application of hybrid anticancer molecules requires further investigation. There is a great interest in developing new site-specific anticancer agents able to efficiently destroy cancer cells with minimal toxic side effects. Serum proteins are known to play an important role as drug delivery system with important clinical applications. Hence, the conjugation of testo and testo-Pt(II) (two semi-synthetic testosterone derivatives) with human serum albumin HSA), bovine serum albumin (BSA) and beta-lactoglobulin (β-LG) was investigated in aqueous solution at physiological pH. Multiple spectroscopic methods, thermodynamic analysis and modeling were used to determine the binding efficacy of these bioactive compounds to serum proteins. Drug-protein conjugation occurred via ionic contacts. BSA forms more stable conjugates than HSA and β-LG with the order of stability testo > testo-Pt(II). Major alterations of protein secondary structures were observed upon drug complexation. Serum proteins can be used to deliver these bioactive materials in vitro.

Multispectroscopic and molecular modeling approach to investigate the interaction of diclofop-methyl enantiomers with human serum albumin

Pesticides and related environmental contaminants have always been threated to human health due to their intrinsic toxicity. In the context of this contribution, the interaction between diclofop-methyl (DM) enantiomers and human serum albumin (HSA) has been characterized by steady state and three-dimensional fluorescence, molecular modeling, circular dichroism (CD) and ultraviolet–visible (UV–vis) spectroscopy. The binding constants significantly showed the binding was enantioselective and HSA had higher affinity for S-DM. The thermodynamic parameters of the binding reaction (ΔG, ΔH and ΔS) clearly signified that hydrophobic effects and H-bonds contribute to the formation of DM-HSA complex. The alterations of protein secondary structure in the presence of DM enantiomers were confirmed by CD spectroscopy, UV–vis and three-dimensional fluorescence spectroscopy. In addition, both fluorescence probe study and molecular modeling simulation evidenced the binding of DM enantiomers to HSA primarily took place in subdomain IIIA (Sudlow׳s site II). This investigation highlights the binding mechanism, specific binding sites and binding region of DM enantiomers on human serum albumin at the first time. Besides, such task can provide important insight to the interaction of the physiological protein HSA with chiral aryloxyphenoxypropionate herbicides and give support to the human health risk assessment.

Studies on the interaction mechanism for human serum albumin with hexythiazox

The interaction of human serum albumin (HSA) with hexythiazox (HEX) and the alterations of protein secondary structure in the presence of HEX were investigated by molecular docking, UV-vis absorption spectrometry, synchronous fluorescence spectrometry and three-dimensional fluorescence spectroscopy. Forecasting molecular docking results revealed that HEX could bind on site Ⅰ and site Ⅱ where it was easier to combine in HSA. The experiment results indicated that HEX had a strong ability to quench the intrinsic fluorescence of HSA through static quenching procedure. At the same time, HEX altered HSA surrounding microenvironment and led to change in the peptide chain structure of the protein. Binding affinity ( K A) and the amounts of binding sites ( n ) between HEX and HSA at 298 and 291 K were estimated as 7.35 × 103 mol/L, 0.82 and 1.02 × 104 mol/L, 0.86, respectively, which confirmed that HEX could only bind on site Ⅱ. The binding power between HEX and HSA involved mainly hydrogen bonds, van der Waals and hydrophobic forces, and an apparent distance between the Trp214 and HEX was 3.01 nm. The various informations of these studies help to understand toxicity of pesticide to humans and their bioaccumulative potential at the molecular level.

Studies on the interactions of SAP-1 (an N-terminal truncated form of cystatin S) with its binding partners by CD-spectroscopic and molecular docking methods

SAP-1 is a 113 amino acid long single-chain protein which belongs to the type 2 cystatin gene family. In our previous study, we have purified SAP-1 from human seminal plasma and observed its cross-class inhibitory property. At this time, we report the interaction of SAP-1 with diverse proteases and its binding partners by CD-spectroscopic and molecular docking methods. The circular dichroism (CD) spectroscopic studies demonstrate that the conformation of SAP-1 is changed after its complexation with proteases, and the alterations in protein secondary structure are quantitatively calculated with increase of α-helices and reduction of β-strand content. To get insight into the interactions between SAP-1 and proteases, we make an effort to model the three-dimensional structure of SAP-1 by molecular modeling and verify its stability and viability through molecular dynamics simulations and finally complexed with different proteases using ClusPro 2.0 Server. A high degree of shape complementarity is examined within the complexes, stabilized by a number of hydrogen bonds (HBs) and hydrophobic interactions. Using HB analyses in different protein complexes, we have identified a series of key residues that may be involved in the interactions between SAP-1 and proteases. These findings will assist to understand the mechanism of inhibition of SAP-1 for different proteases and provide intimation for further research.

Synchrotron FTIR microspectroscopy of Escherichia coli at single-cell scale under silver-induced stress conditions

The present work was focused on elucidating biochemical changes in the model bacterium Escherichia coli exposed to ionic silver mediated stress, at a single-cell scale. In order to achieve this, in situ synchrotron Fourier-transform infrared (sFTIR) microspectroscopy was performed, for the first time, on individual cells by attenuated total reflectance (ATR) combined with the use of zinc-selenide hemisphere for high spatial resolution. In a first part, the potential of the method was evaluated on bacteria subjected to a lethal 100 μM AgNO(3) concentration for 2 h compared to untreated 100 % viable cells. Differences in cell composition were assessed for the C-H stretching and protein spectral regions, indicating that the inhibitory action was targeted against both fatty acids and proteins. Transmission electron microscopy (TEM) confirmed morphological damages of the cell ultrastructure. The relevance of ATR-sFTIR microspectroscopy for highlighting the heterogeneity in Ag(+)-mediated effects within a given bacterial population was also pointed out. In a second part, cells were exposed to sub-lethal Ag(+) concentrations (<10 μM AgNO(3)) tested under "dynamic" growth mode: early addition vs. pulse in the mid-exponential phase, and compared to simultaneously batch-grown untreated bacteria or cells sampled just before the pulse, respectively. sFTIR microspectroscopy and TEM imaging were performed in close relation with growth kinetics characterization. No significant effect of the Ag(+) pulses was detected, in accordance with macrokinetics data. For early-treated cells, effects on fatty acid composition were shown, although no major alteration of protein secondary structure was noticed. These partial effects were consistent with TEM observations and growth kinetics.

Binding of the endocrine disruptors 4-tert-octylphenol and 4-nonylphenol to human serum albumin

Alkylphenols, considered to be endocrine disruptor chemicals and toxic environmental priority pollutants, pose great threats to humans with wide exposure from food and other potential sources. In this paper, to evaluate the toxicity of the alkylphenols at the protein level, the effects of 4-tert-octylphenol (OP) and 4-nonylphenol (NP) on human serum albumin (HSA) were characterized by molecular modeling, steady state and time-resolved fluorescence, ultraviolet–visible spectroscopy (UV–vis) and circular dichroism spectroscopy (CD). The enthalpy change (ΔH) and entropy change (ΔS) indicated that hydrophobic forces and hydrogen bonds were the dominant intermolecular forces in the binding of the alkylphenols to HSA. The binding constant of HSA–NP is much greater than that of HSA–OP, revealing that NP, which has a longer carbon chain, has a higher affinity than OP. The alterations of protein secondary structure in the presence of the alkylphenols were confirmed by UV–vis and CD spectroscopy. The time-resolved fluorescence study showed that the lifetimes of tryptophan (Trp) residue of HSA decreased after the addition of the alkylphenols, NP with longer carbon chain impact on the average lifetime of the Trp of HSA more than OP, which consistent with the conclusion drawn from the fluorescence date.

In vitro study on the binding of gemcitabine to bovine serum albumin

In the present study, the interaction of gemcitabine and bovine serum albumin (BSA) has been characterized by spectroscopic methods (fluorescence, UV–vis, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy) and molecular docking. Gemcitabine quenched BSA fluorescence in a static mode with binding constants of 6.61, 6.18, and 3.44×104M−1 at 290, 300, and 310K, respectively. Meanwhile, the number of binding site was found to be approximately 1 from fluorescence titration data. The calculated thermodynamic parameters represent a spontaneous process and electrostatic force dominated binding, which was confirmed by the docking study. Furthermore, the alterations of protein secondary structure in the presence of gemcitabine were assessed by CD UV–vis and FT-IR spectroscopy. Fluorescence resonance energy transfer (FRET) analysis proved high probability of energy transfer from Trp residue to the drug molecule.

Structural alterations in rat liver proteins due to streptozotocin-induced diabetes and the recovery effect of selenium: Fourier transform infrared microspectroscopy and neural network study

The relation between protein structural alterations and tissue dysfunction is a major concern as protein fibrillation and/or aggregation due to structural alterations has been reported in many disease states. In the current study, Fourier transform infrared microspectroscopic imaging has been used to investigate diabetes-induced changes on protein secondary structure and macromolecular content in streptozotocin-induced diabetic rat liver. Protein secondary structural alterations were predicted using neural network approach utilizing the amide I region. Moreover, the role of selenium in the recovery of diabetes-induced alterations on macromolecular content and protein secondary structure was also studied. The results revealed that diabetes induced a decrease in lipid to protein and glycogen to protein ratios in diabetic livers. Significant alterations in protein secondary structure were observed with a decrease in α-helical and an increase in β-sheet content. Both doses of selenium restored diabetes-induced changes in lipid to protein and glycogen to protein ratios. However, low-dose selenium supplementation was not sufficient to recover the effects of diabetes on protein secondary structure, while a higher dose of selenium fully restored diabetes-induced alterations in protein structure.

Effects of poly(ethylene oxide) and pH on the electrospinning of whey protein isolate

AbstractPoly(ethylene oxide) (PEO) is known for facilitating the electrospinning of biopolymer solutions, which are otherwise not electrospinnable. The objective of this study was to improve the understanding of the positive effects of PEO on the electrospinning of whey protein isolate (WPI) solutions under different pH conditions. Alterations in protein secondary structure and polymer solution properties (viscosity, conductivity, and dynamic surface tension), as induced by pH changes, significantly affected the electrospinning behavior of WPI/PEO (10% w/w: 0.4% w/w PEO) solutions. Acidic solutions resulted in smooth fibers (707 ± 105 nm) while neutral solutions produced spheres (2.0 ± 1.0 μm) linked with ultrafine fibers (138 ± 32 nm). In comparison, alkaline solutions produced fibers (191 ± 36 nm) that were embedded with spindle‐like beads (1.0 ± 0.5 μm). 13C NMR and FTIR spectroscopies showed that the increase in random coil and α‐helix secondary structures in WPI were the main contributors to the formation of bead‐less electrospun fibers. The electrospinning‐enabling properties of PEO on aqueous WPI solutions were attributed to physical chain entanglement between the two polymers, rather than specific polymer–polymer interactions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Spectroscopic, structural and thermodynamic properties of chlorpyrifos bound to serum albumin: A comparative study between BSA and HSA

Chlorpyrifos (CPF) is a widely used organophosphate insecticide which could bind with human serum albumin (HSA) and bovine serum albumin (BSA). The binding behavior was studied employing fluorescence, three-dimensional fluorescence, Circular dichroism (CD) spectroscopy, UV–vis absorption spectroscopy, electrochemistry and molecular modeling methods. The fluorescence spectra revealed that CPF causes the quenching of the fluorescence emission of serum albumin. Stern–Volmer plots were made and quenching constants were thus obtained. The results suggested the formation of the complexes of CPF with serum albumins, which were in good agreement with the results from electrochemical experiments. Association constants at 25°C were 3.039×105molL−1 for HSA, and 0.3307×105molL−1 for BSA, which could affect the distribution, metabolism, and excretion of pesticide. The alterations of protein secondary structure in the presence of CPF were confirmed by the evidences from UV and CD spectra. Site competitive experiments also suggested that the primary binding site for CPF on serum albumin is close to tryptophan residues 214 of HSA and 212 of BSA, which was further confirmed by molecular modeling.

Study on the interaction of tamiflu and oseltamivir carboxylate with human serum albumin

Oseltamivir phosphate (OP; tamiflu) is an antiviral pro-drug, which is hydrolyzed hepatically to the active metabolite oseltamivir carboxylate (OC). It is the first orally neuraminidase inhibitor that was used in the treatment and prophylaxis of influenza virus A and B infection. Human serum albumin (HSA) is the most abundant of the proteins in the blood plasma and is major transporter for delivering several drugs in vivo. This study was designed to examine the interaction of HSA with oseltamivir phosphate (OP) and oseltamivir carboxylate (OC) in aqueous solution at physiological conditions, using a constant protein concentration and various drug contents. FTIR, UV–Vis spectroscopic methods were used to determine the drugs binding mode, the binding constant and the effects of drug complexation on protein secondary structure. Structural analysis showed that OP and OC bind HSA via polypeptide polar groups with overall binding constants of K OP–HSA = 3.86(±1.05) × 10 3 M −1 and K OC–HSA = 1.5(±0.45) × 10 2 M −1. The alterations of protein secondary structure are attributed to a partial destabilization of HSA on drug complexation. The protein secondary structure showed no major alterations at low drugs concentrations (50 μM), whereas at higher content (1 mM), decrease of α-helix from 58% (free HSA) to 38% (OP–HSA)–48% (OC–HSA), decrease of random coil from 15% (free HSA) to 2% (OP–HSA)–3% (OC–HSA), increase of β-sheet from 6% (free HSA) to 20% (OC–HSA)–29% (OP–HSA) and turn from 8% (free HSA) to 17% (OC–HSA)–19% (OP–HSA) occurred in the drug–HSA complexes. These observations indicated that low drug content induced protein stabilization, whereas at high drug concentration, a partial protein destabilization occurred in these drug–HSA complexes.