near-UV Circular Dichroism Spectra Research Articles

Enhanced and suppressed phosphorus mineralization by Ca complexation: NMR and CD spectroscopy investigation

With the increasing demand for P fertilizer for world food production, the use of soil organic P fraction via mineralization could become an important P resource in agricultural soils. However, the predominant organic P species, phytic acid, has been considered rather recalcitrant to mineralization due to its active interaction with dissolved metals like Ca2+ in soil pore water. Calcium ions can be an inhibitor to many phytases, yet the mechanism was not clear. The objective of this study was to understand the effects of Ca2+(aq) on the phytase activity and inhibitory mechanisms using batch degradation kinetic experiments, Nuclear Magnetic Resonance (NMR) spectroscopy, Saturation Transfer Difference (STD) NMR, and Circular dichroism (CD) spectroscopy. The phytase activity followed Michaelis-Menten kinetics and increased Michaelis constant Km and decreased Vmax with Ca2+ addition were observed at pH 6. Therefore, mixed inhibition was the inhibition mechanism which was likely a result of the allosteric effect of Ca2+. The near-UV CD spectra supported phytase secondary conformational change upon the interaction between Ca2+ and the enzyme. It was found that phytase initially reacted with the D/L-3 phosphate of phytic acid at pH 6. At pH 8, the overall phytase activity decreased, yet the effect of Ca2+ on phytase activity was the opposite of that of pH 6. Enhanced phytase activity with Ca2+ addition was attributed to the structural change of phytic acid upon the Ca2+ complexation, which was confirmed by NOE spectra. The Ca2+-phytic acid complex might be a more favorable substrate than the free phytic acid. Unlike the findings from pH 6, Ca2+ didn't induce significant changes in either the near- or far-UV region of the CD spectra at pH 8. Furthermore, P5 was found to be the target of phytase at pH 8. The study revealed the pH-specific effects of Ca2+ on the mineralization of phytic acid

Circular Dichroism Spectra of α-Chymotrypsin-SDS Solutions Depend on the Procedure of Their Preparation.

We recorded the far- and near-UV circular dichroism (CD) spectra of solutions of α-chymotrypsin and sodium dodecyl sulfate (SDS) with the final surfactant concentration significantly above the critical micellization concentration. Solutions were prepared using three different procedures. The reference procedure was to mix the chymotrypsin solution with the SDS solution once, immediately achieving the final SDS concentration. In alternative procedures, the protein solutions initially contained some SDS and were mixed with pure SDS solutions at a concentration to provide the same final surfactant as the reference mixing. We demonstrate that the supplementation to the selected final concentration of SDS of the pure chymotrypsin solution leads to different CD spectra than the supplementation to this final concentration of SDS in the chymotrypsin solution containing a small concentration of a few millimolar SDS. These differences disappear when the initial concentration of SDS in the protein solution, which we then supplement to the indicated final concentration, is higher. This suggests the irreversibility of the processes caused by the addition of SDS to chymotrypsin and the influence of the initial amount of this surfactant on the processes occurring with its further addition to the solution. For quantitative analysis of far-UV CD spectra in terms of populations of protein secondary structure elements, we used four well-established software packages. All programs consistently indicate that the observed differences in the far-UV CD spectra can be explained by the differences in the increase in the population of helical forms in chymotrypsin under the influence of SDS.

Comparative Study of the Structural and Functional Properties of Membrane-Isolated and Isoelectric pH Precipitated Green Lentil Seed Protein Isolates.

The demand for isolated seed proteins continues to increase but functionality in food systems can be greatly dependent on the extraction method. In this work, we report the physicochemical and functional properties of lentil seed proteins isolated using various protocols. Lentil flour was defatted followed by protein extraction using isoelectric pH precipitation (ISO) as well as NaOH (MEM_NaOH) and NaCl (MEM_NaCl) extractions coupled with membrane ultrafiltration. The MEM_NaCl had significantly (p < 0.05) higher protein content (90.28%) than the ISO (86.13%) and MEM_NaOH (82.55%). At pH 3–5, the ISO was less soluble (2.26–11.84%) when compared to the MEM_NaOH (25.74–27.22%) and MEM_NaCl (27.78–40.98%). However, the ISO had higher yield and protein digestibility (48.45% and 89.82%) than MEM_NaOH (35.05% and 77.87%) and MEM_NaCl (13.35% and 77.61%), respectively. Near-UV circular dichroism spectra showed that the MEM_NaOH had loose tertiary conformation at pH 3, 5, 7 and 9 while ISO and MEM_NaCl had more compact structures at pH 7 and 9. The three protein isolates formed better emulsions (lower oil droplet sizes) at pH 7 and 9 when compared to pH 3 and 5. In contrast, foaming capacity was better at pH 5 than pH 3, 7, and 9.

Higher-Order Structure Comparison of a Proposed Biosimilar and the Innovator Biotherapeutic Trastuzumab using Circular Dichroism Coupled with Statistical Analysis

We employ a novel circular dichroism (CD) technology coupled with statistical analysis to assess the higher-order structure (HOS) similarity of commercially available trastuzumab and a proposed biosimilar. This technology shows good potential for enabling the comparison of similarities and differences in secondary and tertiary structures of proteins. Multiple CD spectra in far- and near-UV are obtained reproducibly from a CD spectrometer with fully integrated autosampler and flow cell to eliminate the errors typically associated with sample handling on manual CD spectrometers. The significance of similarities or differences was quantified statistically using three analytical methods (weighted spectral difference, correlation coefficient, and area of overlap). HOS comparison of the secondary structure (far-UV CD spectra) suggested similarity between the innovator drug, trastuzumab (Herceptin®), and biosimilar products. However, the tertiary structure (near-UV CD spectra) suggested statistically significant differences. These differences may be due to changes in tertiary structure or to modifications and degradations during the process of production or storage. The results show that the automated circular dichroism technology coupled with statistical analysis is a robust tool for enabling the comparison of similarities and differences in secondary and tertiary structures of protein products.

Dual modifications on the gelatinization, textural, and morphology properties of pea starch by sodium carbonate and Mesona chinensis polysaccharide

The effects of dual modifications on the gelatinization, textural, and morphology properties of pea starch by Na2CO3 and Mesona chinensis polysaccharide (MCP) were investigated. Results showed that Na2CO3 promoted granular swelling and disruption but decreased the rearrangement tendency of disordered starch fraction of PS during gelatinization. The addition of 0.05%–0.1% MCP slightly affected granular swelling and protected the integrity of starch granules of Na2CO3–PS. 0.2% MCP enhanced the retrogradation and recrystallization of gelatinized starch in the presence of Na2CO3. Near-UV circular dichroism spectra showed that adding Na2CO3 and MCP in PS resulted in a strong peak at 285 nm and a small trough at 310 nm in the spectra of MCP and PS. The peak intensity orders of samples were consistent with the reaggregation tendency, suggesting that the characteristic peak at 285 nm was closely related to the retrogradation degree of starch.

P5722Thermodynamic phenotypes guide the pathogenicity assessment of a variant of uncertain significance in cardiac myosin binding protein C

Abstract In the era of Next Generation Sequencing (NGS), genetic testing for inherited disorders identifies an ever-increasing number of variants, whose pathogenicity remains unclear. These variants of uncertain significant (VUS) limit the reach of genetic testing in clinical practice. The VUS for Hypertrophic Cardiomyopathy (HCM), the most common familial heart disease, constitute over 60% of entries for missense variants shown in ClinVar database. We have proposed a workflow to determine pathogenicity of VUS, which integrates bioinformatics evaluation and functional studies of RNA splicing and protein thermodynamic stability. This workflow was applied on a novel VUS in MYBPC3 gene, coding for cardiac myosin-binding protein C (cMyBP-C), which is the most mutated gene in HCM. The c.1809T&gt;G-p.I603M variant was identified during genetic screening of patient clinically affected by HCM and it was classified as VUS applying ACMG criteria. In silico prediction and mRNA analysis of c.1809T&gt;G-p.I603M variant indicated no alteration of RNA splicing (Figure 1). At protein level, the p.I603M mutation maps to the C4 domain of cMyBP-C. The homology modelling of domain C4 shows I603 to be buried in the protein structure, suggesting a potential destabilising role of this mutant. The Circular Dichroism (CD) confirms that the I603M variant does not perturb much the structure of domain, according to the far-UV and near-UV CD spectra. However, the thermodynamic stability of domain C4 is severely compromised, as shown by lower Tm and van't Hoff enthalpy (ΔHv) in thermal denaturation experiments by CD and Differential Scanning Calorimetry (DSC) (Figure 1). Furthermore, the Gibbs free energy change (ΔG) at 25°C of the unfolding process was also calculated from the DSC thermograms. The resulting ΔΔG of C4 I603M (4.5 kcal/mol) is comparable to other pathogenetic variants in other MYBPC3 domains. Taking into account our results, we propose reclassification of variant p.I603M as likely pathogenic. Figure 1. Workflow In conclusion, our strategy is useful to refine the assignment of pathogenicity in the absence of enough genetic support, improving the clinical management of HCM patients and their families. Acknowledgement/Funding MCNU: BIO2014-54768-P, BIO2017-83640-P (AEI/FEDER, UE), RYC-2014-16604, SEV-2015-0505- ISCIII: CB16/11/00425. Comunidad de Madrid: PEJ16/MED/TL-1593.

DichroCalc: Improvements in Computing Protein Circular Dichroism Spectroscopy in the Near-Ultraviolet

A fully quantitative theory connecting protein conformation and optical spectroscopy would facilitate deeper insights into biophysical and simulation studies of protein dynamics and folding. The web server DichroCalc (http://comp.chem.nottingham.ac.uk/dichrocalc) allows one to compute from first principles the electronic circular dichroism spectrum of a (modeled or experimental) protein structure or ensemble of structures. The regular, repeating, chiral nature of secondary structure elements leads to intense bands in the far-ultraviolet (UV). The near-UV bands are much weaker and have been challenging to compute theoretically. We report some advances in the accuracy of calculations in the near-UV, realized through the consideration of the vibrational structure of the electronic transitions of aromatic side chains. The improvements have been assessed over a set of diverse proteins. We illustrate them using bovine pancreatic trypsin inhibitor and present a new, detailed analysis of the interactions which are most important in determining the near-UV circular dichroism spectrum.

Effects of high hydrostatic pressure on Rhizopus chinensis lipase: II. Intermediate states during unfolding

Abstract High hydrostatic pressure (HHP) is currently considered a well-established technology for processing food and biological materials and there is an interest in investigating the changes in the structural and functional properties of these materials after high pressure treatment. Therefore, the changes in the structure of Rhizopus chinensis lipase (RCL) after high hydrostatic pressure treatment were investigated. Far-UV circular dichroism (CD) spectra showed that the secondary structure of RCL is maintained at pressures below 400 MPa and becomes gradually disordered after higher pressures are applied. Near-UV CD spectra showed that the RCL begins to lose its tertiary structure at pressure over 400 MPa. Fluorescence quenching and the binding of 1-anilinonaphtha-lene-8-sulfonate confirmed that a partially unfolded intermediate, with loosely compacted conformation and hydrophobic regions, is formed at a pressure of 600 MPa. These results also suggest that RCL maintains a native-like state at pressures below 400 MPa. Above 500 MPa RCL molecules showed characteristics of being in a molten globule state. Dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements indicated that RCL molecules at these pressures are aggregating. The addition of (NH4)2SO4 to the protein solution could prevent the aggregation, and at 600 MPa the molecule had a hydrodynamic radius approximately 8% larger than that observed for the control sample, which was regarded as being in the molten globule state. The observations suggest that at increasing pressures, the unfolding mechanism of RCL follows well-defined steps from a native state via a native-like structure ending in molten globular state or molecular aggregation.

Effects of Disulfide Bond Reduction on the Conformation and Trypsin/Chymotrypsin Inhibitor Activity of Soybean Bowman-Birk Inhibitor.

Soybean seeds contain three groups (A, C, and D) of Bowman-Birk inhibitors (BBIs). In this study, highly purified BBI-A (approximately 96%) was obtained from soybean whey at the 0.1 g level by the complex coacervation method. BBI-A has seven disulfide bonds (SS) and no sulfhydryl group and exhibits trypsin inhibitor activity (TIA) and chymotrypsin inhibitor activity (CIA). The X-ray structure has shown that BBI-A has five exposed SS and two buried SS. Because of steric hindrance, it was reasonable to consider that dithiothreitol first attacks the five exposed SS and then the two buried SS, which was supported by the results that SS reduction with dithiothreitol could be divided into quick and slow stages, and the critical point was close to 5/7. The effects of SS reduction on TIA and CIA could be divided into three stages: when one exposed SS was reduced, both TIA and CIA decreased to approximately 60%; with further reduction of exposed SS, CIA gradually decreased to 8% and TIA gradually decreased to 26%; with further reduction of buried SS, CIA gradually decreased to 2% and TIA slightly decreased to 24%. Far-ultraviolet (far-UV) circular dichroism (CD) spectra showed that the secondary structure of BBI-A was slightly changed, whereas near-ultraviolet (near-UV) CD spectra showed that the conformation of BBI-A was substantially changed after the five exposed SS were reduced; further reduction of buried SS affected the conformation to some extent. The results of Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and from a C8 column showed the same trend as near-UV CD spectra. BBI-A has a structural peculiarity in that two hydrophobic patches are exposed to the exterior (in contrast to typical soluble proteins), which was attributed to the seven SS by some researchers. These results support the hypothesis that hydrophobic collapse of the exposed hydrophobic patches into a regular hydrophobic core occurred after the reduction of SS in BBI-A.

Structural analyses combined with small-angle X-ray scattering reveals that the retention of heme is critical for maintaining the structure of horseradish peroxidase under denaturing conditions.

We analyzed the structure of horseradish peroxidase (HRP) under denaturing conditions of 9M urea or 6M guanidine hydrochloride (GdnHCl). Far-UV circular dichroism (CD) spectra indicated the existence of native-like secondary structure of holo-HRP in 9M urea. In addition, slight changes in near-UV and Soret region CD spectra of holo-HRP in 9M urea suggest that the tertiary structure of holo-HRP and the binding of heme remain partially intact in this condition. A transition in the thermal unfolding transition curve of holo-HRP in 9M urea indicated the existence of a considerable amount of secondary structure. However, no secondary structure, tertiary structure, or interaction between heme and HRP were observed in holo-HRP in 6M GdnHCl. Small-angle X-ray scattering indicated that although distal and proximal domains of holo-HRP in 9M urea might be partially unfolded, the central region that contains the heme might maintain its tertiary structure. Our results suggest that retention of the heme is essential for maintenance of the structure of HRP under highly denaturing conditions.

Development of a subunit vaccine for prevention of Clostridium difficile associated diseases: Biophysical characterization of toxoids A and B

Inactivation of bacterial toxins for use in human vaccines traditionally is achieved by treatment with formaldehyde. In contrast, the bivalent experimental vaccine for the prevention of C. difficile infections (CDI) that is currently being evaluated in clinical trials was produced using a different strategy. C. difficile toxins A and B were inactivated using site-directed mutagenesis and treatment with 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride/N-hydroxysulfosuccinimide (EDC/NHS). In the present work we investigate the effect of genetic and chemical modifications on the structure of inactivated toxins (toxoids) A and B. The far-UV circular dichroism (CD) spectra of wild type toxins, mutated toxins, and EDC/NHS-inactivated toxoids reveal that the secondary structure of all proteins is very similar. The near-UV CD spectra show that aromatic residues of all proteins are in a unique asymmetric environment, indicative of well-defined tertiary structure. These results along with the fluorescence emission maxima of 335nm observed for all proteins suggest that the tertiary structure of toxoids A and B is preserved as well. Analytical ultracentrifugation data demonstrate that all proteins are predominantly monomeric with small fractions of higher molecular weight oligomeric species present in toxoids A and B. Differential scanning calorimetry data reveal that genetic mutations induce thermal destabilization of protein structures. Subsequent treatment with EDC/NHS results either in a minimal (1°C) increase of apparent thermostability (toxoid B) or no change at all (toxoid A). Therefore, our two-step inactivation strategy is an effective approach for the preparation of non-toxic proteins maintaining native-like structure and conformation.

Quantitative first principles calculations of protein circular dichroism in the near-ultraviolet.

Vibrational structure in the near-UV circular dichroism (CD) spectra of proteins is an important source of information on protein conformation and can be exploited to study structure and folding. A fully quantitative theory of the relationship between protein conformation and optical spectroscopy would facilitate deeper interpretation of and insight into biophysical and simulation studies of protein dynamics and folding. We have developed new models of the aromatic side chain chromophores toluene, p-cresol and 3-methylindole, which incorporate ab initio calculations of the Franck-Condon effect into first principles calculations of CD using an exciton approach. The near-UV CD spectra of 40 proteins are calculated with the new parameter set and the correlation between the computed and the experimental intensity from 270 to 290 nm is much improved. The contribution of individual chromophores to the CD spectra has been calculated for several mutants and in many cases helps rationalize changes in their experimental spectra. Considering conformational flexibility by using families of NMR structures leads to further improvements for some proteins and illustrates an informative level of sensitivity to side chain conformation. In several cases, the near-UV CD calculations can distinguish the native protein structure from a set of computer-generated misfolded decoy structures.

Recombinant Human Serum Albumin Containing 3 Copies of Domain I, Has Significant in Vitro Antioxidative Capacity Compared to the Wild-Type

Human serum albumin (HSA), the most abundant protein in serum, functions as carrier of drugs and contributes to maintaining serum colloid osmotic pressure. We report herein on the preparation of a genetic recombinant HSA, in which domains II and III were changed to domain I (triple domain I; TDI). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results indicated that the purity of the TDI was equivalent to that of the wild type (WT). Both far- and near-UV circular dichroism (CD) spectra of the TDI showed that its structural characteristics were similar to the WT. Ligand binding capacity was examined by an ultrafiltration method using 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) and ketoprofen as markers for site I and site II, respectively. The binding capacity of TDI for both ligands was lower than that for the wild type. TDI significantly suppressed the oxidation of dihydrorhodamine 123 (DRD) by H2O2 compared to the WT. Our current results suggest that TDI has great potential for further development as HSA a product having antioxidative functions.

Tryptophan Residues from Cap Binding Slot in eIF4E Family Members: Their Contributions to Near-UV Circular Dichroism Spectra

eIF4E, a key factor in the cap-dependent translation initiation, binds cap structure at the 5’ end of mRNA by stacking interaction involving two of its eight conserved tryptophan residues. In this paper, we examined individual contributions of tryptophan residues to the near-UV Circular Dichroism spectra to identify structural similarities and differences in cap binding motif among members of eIF4E family. The near-UV CD spectrum of human eIF4E1a in its apo form, resulting mainly from 1Lb transition and dominated by two vibrionic bands, is conserved among eIF4Es. Based on comparison of CD spectra for eIF4E mutants, we showed that tryptophans involved in stacking interaction give strongest individual contributions, which allow identification of their different orientation with respect to the cap. This indicates that near-UV CD is a quick and powerful tool to analyse tryptophan conformation in eIF4E proteins, and their changes upon binding modified cap analogues.

Estimating analytical variability in two-dimensional data

Throughout the course of drug development there are many instances in which a variability assessment within a set of analytical data is required, which may be challenging for techniques that produce two-dimensional data. This note describes an interval-based approach to variability assessment and demonstrates its applicability for analysis of near-UV circular dichroism (CD) spectra. The approach is generalizable and could be applied to two-dimensional data from other analytical techniques as well.

Cloning and expression of phosphoenolpyruvate carboxykinase from a cestode parasite and its solubilization from inclusion bodies using l-arginine

Phosphoenolpyruvate carboxykinase is an essential regulatory enzyme of glycolysis in the cestode parasite, Raillietina echinobothrida, and is considered a potential target for anthelmintic action because of its differential activity from that of its avian host. However, due to the unavailability of its structure, the mechanism of regulation of PEPCK from R. echinobothrida (rePEPCK) and its interaction with possible modulators remain unclear. Hence, in this study, the rePEPCK gene was cloned into pGEX-4T-3 and overexpressed for its characterization. On being induced by IPTG, the recombinant rePEPCK was expressed as inclusion bodies (IBs); hence, various agents, like different inducer concentrations, temperature, time, host cell types, culture media, pH, and additives, were used to bring the protein to soluble form. Finally, a significant amount (∼46%) of rePEPCK was solubilized from IBs by adding 2M l-arginine. Near-UV circular dichroism spectra analysis indicated that l-arginine (2M) had no effect on the conformation of the protein. In this study, we have reported a yield of ∼73mg of purified rePEPCK per 1L of culture. The purified rePEPCK retained its biological activity, and Km of the enzyme for its substrate was determined and discussed. The availability of recombinant rePEPCK may help in biochemical- and biophysical-studies to explore its molecular mechanisms and regulations.

Probing Tertiary Structure of Proteins Using Single Trp Mutations with Circular Dichroism at Low Temperature

Trp is the most spectroscopically informative aromatic amino acid of proteins. However, the near-UV circular dichroism (CD) spectrum of Trp is complicated because the intensity and sign of 1La and 1Lb bands vary independently. To resolve vibronic structure and gain site-specific information from complex spectra, deconvolution was combined with cooling and site-directed tryptophan substitution. Low temperature near-UV CD was used to probe the local tertiary structure of a loop and α-helix in tear lipocalin. Upon cooling, the enhancement of the intensities of the near-UV CD was not uniform, but depends on the position of Trp in the protein structure. The most enhanced 1Lb band was observed for Trp at position 124 in the α-helix segment matching the known increased conformational mobility during ligand binding. Some aspects of the CD spectra of W28 and W130 were successfully linked to specific rotamers of Trp previously obtained from fluorescence lifetime measurements. The discussion was based on a framework that the magnitude of the energy differences in local conformations governs the changes in the CD intensities at low temperature. The Trp CD spectral classification of Strickland was modified to facilitate the recognition of pseudo peaks. Near-UV CD spectra harbor abundant information about the conformation of proteins that site directed Trp CD can report.

Switching the enzymatic activity of ribonuclease a based on enzyme/polymer complex formation

Context: Enzymes are ideal for various applications in both medicine and biotechnology. Switching on/off the enzymatic activity of enzymes by polymeric modification would expand the applications of enzymes in a wide range of research fields. Objectives: On/off switching the enzymatic activity of RNase A and the confirmation of the enzyme/polymer complex formation which leads to improve the heat resistance of RNase A. Materials and Methods: ?-Methoxy-?-methacryloyl poly (ethylene glycol) (PEG-MA) macromonomer and PEAMA-g-PEG were synthesized. Bovine RNase A, cytidine 2?,3?-cyclic monophosphate sodium salt (cCMP), and 3-(N-morpholino)propanesulfonic acid (MOPS) were obtained from Sigma Chemical Co. (St. Louis, USA). PAAc (Mn = 5,000 g/mol) were purchased from Wako (Osaka, Japan). Sodium dihydrogen phosphate dihydrate (NaH2PO4.2H2O) was obtained from Nacalai Tesque Inc. (Kyoto, Japan). The enzymatic activity of RNase A was estimated as follows. The RNase A concentration was determined by measuring the absorbance at 280 nm with an appropritate blank, using an extinction coefficient of 7.10 mL mg-1 cm-1. A total of 1.5 mL of 0.1 mg/mL cCMP solution prepared in 0.1 M MOPS (pH 7.0) was mixed with 10 ?L of the RNase A solution in 50 mM sodium phosphate buffer (pH 7.0). The increase in light scattering intensity of the solution was monitored by measuring the absorbance at 284 nm for 60 s in a UV-vis spectrophotometer at room temperature. After heat treatment, the enzymatic activities were measured. Far-UV and near-UV CD spectra were monitored using a spectropolarimeter (model J-720W; Jasco, Tokyo, Japan). Results: We have found that poly (acrylic acid) (PAAc) suppressed the enzymatic activity of RNase A completely and the recovery of enzymatic activity were observed (94%) by the external addition of PEAMA-g-PEG to the RNase A/PAAc complex. Our present findings suggest that the complexation between PEAMA-g-PEG and RNase A has occurred which improve the heat resistance (64%) of RNase A. Heat treatment has been carried out at 98°C for 10 minutes where the native RNase A lost all of its enzymatic activity. CD spectral analysis also indicates that the conformation of the enzyme was not altered due to the complexation. Conclusion: Poly (N,N-diethylaminoethyl methacrylate)-graft-poly (ethylene glycol) (PEAMA-g-PEG) restored the enzymatic activity of RNase A completely which was inactivated upon the addition of poly(acrylic acid) (PAAc) to RNase A. Complexation of RNase A with PEAMA-g-PEG induced the improvement of heat resistance of RNase A . Circular dichroism (CD) spectral analysis clearly indicated that the complexation of enzyme with polymer has almost no influence on the conformation of enzyme. DOI: http://dx.doi.org/10.3329/jbs.v20i0.17650 J. bio-sci. 20: 33-39, 2012

Circular Dichroism Spectroscopic Detection of Ligand Binding Induced Subdomain IB Specific Structural Adjustment of Human Serum Albumin

This work demonstrates for the first time that binding of various compounds within subdomain IB of human serum albumin (HSA) provokes characteristic changes in the near-UV circular dichroism (CD) spectrum of the protein. It can be inferred from the spectroscopic features of difference ellipticity signals and from CD displacement experiments that tyrosine residues located in subdomain IB are the source of the observed spectral alterations. It is proposed that inclusion of some ligand molecules (bile acids, dehydroepiandrosterone sulfate, steroidal terpenes, fatty acids, ibuprofen, and gemfibrozil) into the pocket of subdomain IB disrupts the Tyr138-Tyr161 interhelical π-π stacking interaction, which is reflected in the CD spectrum. This phenomenon can be utilized for the CD detection of subdomain IB specific binding of endo- as well as exogenous agents and to study the drug binding associated local conformational adaptation of the HSA molecule.

Molten Globule of Hemoglobin Proceeds into Aggregates and Advanced Glycated End Products

Conformational alterations of bovine hemoglobin (Hb) upon sequential addition of glyoxal over a range of 0–90% v/v were investigated. At 20% v/v glyoxal, molten globule (MG) state of Hb was observed by altered tryptophan fluorescence, high ANS binding, existence of intact heme, native-like secondary structure as depicted by far-UV circular dichroism (CD) and ATR-FTIR spectra as well as loss in tertiary structure as confirmed by near-UV CD spectra. In addition, size exclusion chromatography analysis depicted that MG state at 20% v/v glyoxal corresponded to expanded pre-dissociated dimers. Aggregates of Hb were detected at 70% v/v glyoxal. These aggregates of Hb had altered tryptophan environment, low ANS binding, exposed heme, increased β-sheet secondary structure, loss in tertiary structure, enhanced thioflavin T (ThT) fluorescence and red shifted Congo Red (CR) absorbance. On incubating Hb with 30% v/v glyoxal for 0–20 days, advanced glycation end products (AGEs) were detected on day 20. These AGEs were characterised by enhanced tryptophan fluorescence at 450 nm, exposure of heme, increase in intermolecular β-sheets, enhanced ThT fluorescence and red shift in CR absorbance. Comet assay revealed aggregates and AGEs to be genotoxic in nature. Scanning electron microscopy confirmed the amorphous structure of aggregates and branched fibrils of AGEs. The transformation of α-helix to β-sheet usually alters the normal protein to amyloidogenic resulting in a variety of protein conformational disorders such as diabetes, prion and Huntington's.