Structural characterization of the molten globule and native states of ovalbumin: a 1H NMR study

Exploring the potential of infrared spectroscopy in qualitative and quantitative monitoring of ovalbumin amyloid fibrillation

Amyloid fibrils are highly ordered self-assembled (poly)peptide aggregates with cross-β structural pattern. Ovalbumin was used as a model for exploring the potential of infrared spectroscopy in detecting structural transitions and quantitative monitoring of amyloid fibrillation. Low pH (pH 2) and high temperature (90 °C) over the course of 24 h were conditions applied for amyloid formation. Fibrillation of ovalbumin was monitored by ThT and ANS fluorescence, and SDS PAGE. A significant increase in ThT fluorescence with a plateau reached after 4 h of incubation, without the lag phase, was detected. Structural transitions leading to amyloid fibrillation were analysed using all three Amide regions in ATR-FTIR spectra. Significant changes were detected in Amide I and Amide III region (decrease of α-helix and increase of β-sheet peaks). To establish a fast, precise and simple method for quantitative monitoring of amyloid fibrillation, the Amide I/Amide II ratios of aggregation specific β-sheets (1625 and 1695 cm^-1, respectively) with 1540 cm^-1 as internal standard were used, resulting in good correlation (R² = 0.93 and 0.95) with the data observed by monitoring ThT fluorescence. On the other hand, assessing aggregation specific β-sheet contents by self-deconvolution showed lower correlation with ThT fluorescence (R² = 0.75 and 0.64). Here we examined structural transitions during ovalbumin fibrillation in a qualitative and quantitative manner by exploiting the full potential of Amide regions simultaneously. Secondary structure distribution was monitored using second derivative spectra in Amide I region. A novel, simple mathematical calculation for quantitative monitoring of fibrils formation was presented employing that the increase in low and high frequency aggregation specific β-sheet in Amide I region compared to the internal standard in Amide II region is suitable for fibril formation monitoring.

Equivalent cross-relaxation rate imaging positively correlates with pathological grade and cell density of adipocytic tumors

OBJECTIVE

Equivalent cross-relaxation rate imaging (ECRI) is an MRI technique used to evaluate qualitative changes in protein-water interactions. We aimed to prospectively evaluate the utility of ECRI for classification of adipocytic tumors.

MATERIALS AND METHODS

Institutional Review Board approval was obtained and all patients provided informed consent. Study participants included 40 patients with adipocytic tumors who were diagnosed with lipomas (n=22), atypical lipomatous tissue/well-differentiated liposarcoma (ALT/WDL; n=9), myxoid/round cell liposarcoma (MyL; n=6), and dedifferentiated liposarcoma (DDL; n=3), and 20 control patients for whom subcutaneous fat in the buttock or thigh was analyzed.

RESULTS

Mean ECR values of lipomas, ALT/WDL, and subcutaneous fat were low, and those of MyL and DDL were high. Mean ECR values of MyL and DDL were significantly higher than those of ALT/WDL. The cut-off value was 5.1%. There was a positive correlation between ECR value, pathological grade, and cell density in adipocytic tumors.

CONCLUSION

The ECR value positively correlates with pathological grade and cell density of adipocytic tumors. Our findings suggest that ECRI is a useful method for preoperative evaluation of adipocytic tumors.

Comparative intermolecular cross-relaxation studies of human hemoglobin in red blood cells and bovine serum albumin in solution

Intermolecular cross-relaxation rate (CR) spectra [1/T(IS) (HDO) or 1/T(IS) (H(2) O) vs f(2) (ppm) profiles] for bovine serum albumin [BSA; molecular weight (MW), 66 kDa] solution, partially hydrolyzed BSA gel (BSA*gel) and packed human red blood cells (RBCs) with normal or unstable hemoglobin (Hb; MW, 65 kDa) were studied using f(2) irradiation ranging from - 100 to 100 ppm at γH(2) /2π of 250 Hz. The CR spectra for BSA*gel (pD 4.01, 0.10 M NaCl, 4.83 and 14.39%) exhibited different features in the off-resonance region (below - 2.00 and above 12.0 ppm) relative to that for BSA solution (pD 7.14, 0.10 M NaCl, 14.39%), indicating the association of BSA* molecules in the gel state. The CR spectrum for packed RBCs was compared with those for BSA*gel and BSA solution (14.39%) by correcting for differences in protein concentration. The corrected CR spectrum for packed normal RBCs in the off-resonance region was similar to that for BSA solution, indicating that the physical characteristics of Hb in normal RBCs may be in a solution-like state. Our results on normal RBCs were approximately consistent with the previously reported thermodynamic and hydrodynamic findings that Hb in RBCs and/or in concentrated solution seems to be in a suspension of hard scaled particles.

Comparative 1H NMR studies of saturation transfer in copolymer gels and mouse lenses

Saturation transfer in cross-linked copolymer gels and excised intact and perforating trauma-induced cataract mouse lenses (4- or 8-week-old) were studied using intermolecular cross-relaxation rates (1/T(IS)(H(2)O); 1/T(IS)), monitored with f(2)-irradiation at -8.79, -4.00, and 7.13 ppm (gammaH(2)/2pi approximately 69 Hz). [1] The 1/T(IS)(7.13 ppm) vs dry weight [W (%)] profiles for hydrophilic copolymer gels were far steeper than those for hydrophobic copolymer gels, indicating the participation of an amount of bound water and a number of copolymer hydroxyl groups in the saturation transfer process. In contrast, the 1/T(IS)(-8.79 ppm) vs W (%) profiles exhibited little difference between the hydrophilic and hydrophobic copolymer gels, indicating the major participation of molecular rigidity, i.e. W (%) in the saturation transfer process. [2] The 1/T(IS)(7.13 ppm) values for cataractous mouse lenses were larger than those for intact lenses, indicating the formation of large, immobile lens protein associates or aggregates containing a sufficient amount of bound water for the saturation transfer. [3] The 1/T(IS)(7.13 ppm) vs W (%) profiles for the hydrophilic copolymer gels exhibited similar characteristics to the intact and cataractous mouse lenses with regard to the saturation transfer process.

Cellular density evaluation for malignant lymphoma using equivalent cross-relaxation rate imaging - initial experience

Objective

Equivalent cross-relaxation rate (ECR) imaging is an MRI technique used to evaluate quantitatively a change in the protein-water interaction. We aimed to evaluate retrospectively the usefulness of ECR imaging for the histologic classification of malignant lymphoma (ML).

Materials and Methods

Institutional Review Board approval was obtained and all patients provided informed consent. The study subjects included 15 patients with untreated ML who were histologically diagnosed with follicular lymphoma (FL; n = 8) or diffuse large B-cell lymphoma (DLBCL; n = 7). All patients underwent ECR imaging and the offset frequency was set at 7 ppm.

Results

The median ECR values were 71% (range; 60.7 to 75.5) in FL and 54% (50.8 to 59.4) in DLBCL (p = 0.001). The median cellular density was 1.5 ± 0.17 × 10⁶ / mm² in FL and 1.0 ± 0.70 × 10⁶ / mm² in DLBCL (p = 0.001). The correlation coefficient between the ECR values and cellular density in ML was 0.88 (p = 0.001). In FL and DLBCL, assuming ECR value cut-off points of 60%, both sensitivity and specificity were 100%.

Conclusion

A strong correlation between ECR and cellular density in ML is demonstrated and the ECR may be a useful technique to differentiate between FL and DLBCL.

Some Properties of Lysozyme−Lithium Perfluorononanoate Complexes

Mixtures containing lysozyme, LYSO, and a fully fluorinated surfactant, lithium perfluorononanoate, LiPFN, were investigated in a wide range of concentrations and mole ratios. To ensure consistency to the data, a comparison was made, when possible, with the more conventional SDS as surfactant. Molecular solutions, precipitates, and micellar phases have been observed. The region of existence for each phase depends on the LiPFN/LYSO mole ratios, r, and was determined by different experimental methods. Optical absorbance, CD, 19F NMR, viscosity, electrical conductivity, and dielectric relaxation methods were used. Some methods give information on the protein conformation, others on the state of the surfactant or on the collective system properties, respectively. Addition of LiPFN gives rise to a solution, a poly phase dispersion (at low surfactant to protein ratios) and to a micelle-mediated redissolution of the precipitates. Concomitant to the above macroscopic properties, peculiar effects in the state of LYSO are observed. Low amounts of surfactant reduce significantly the amount of alpha-helix in favor of the beta-sheet conformation of the protein. The former is almost completely regained once micelle-assisted redissolution of the complex occurs. The tertiary structure of the protein, conversely, is lost at low surfactant content and never recovered. Such evidence suggests the occurrence of a molten globule conformation for LYSO in micellar media.

Equivalent cross-relaxation rate imaging for sentinel lymph node biopsy in breast carcinoma

Sentinel lymph node biopsy (SLNB) is an important technique for detecting axillary lymph node metastasis in breast carcinoma patients. However, false-negative results are a problem. Equivalent cross-relaxation rate (ECR) imaging (ECRI) is a measurement method that can be used to quantitatively evaluate a change in the structural organization of lymph nodes by magnetic resonance imaging (MRI). We performed axillary ECRI in an attempt to decrease the false-negative results of SLNB. Regions without metastases showed a higher ECR value. On the other hand, regions with metastases showed a lower ECR value. The ECR images were compared with macroscopic histology images in which the presence or absence of axillary lymph node metastasis could be evaluated. ECRI is a potentially useful method for evaluating the efficacy of SLNB.

Equivalent cross-relaxation rate imaging of breast cancer

PURPOSE

To determine whether equivalent cross-relaxation rate (ECR) imaging is a feasible method for demonstrating breast cancer.

MATERIALS AND METHODS

Fifteen breast cancer patients underwent both ECR imaging, with off-resonance saturation pulses at frequency offsets of 7 and 19 ppm (ECR-7 and ECR-19, respectively) from water resonance, and gadolinium (Gd)-enhanced dynamic magnetic resonance imaging (MRI) of the breast. The mean tumor size was 26.5 mm. The tumor outlines defined by their shape and margin on ECR-7 images were compared with the subtraction images produced by the dynamic study, and the distribution of hyperintensity areas and their shapes on ECR-19 images were assessed. All patients had surgery and pathological findings were compared to ECR images.

RESULTS

The tumor outline of 13/15 (87%) tumors on ECR-7 images was nearly identical to that on subtraction images; ECR-19 images demonstrated the location and degree of fibrosis. The tumor outline of the other two tumors was less clear on ECR-7 images, and internal hyperintensity on ECR-19 images reflected intratumoral fibrotic foci. ECR-7 and -19 imaging findings allowed identification of four distinct tumor types that reflected the tumor growth patterns and their internal structures associated with fibrosis.

CONCLUSION

ECR imaging is a feasible imaging technique for demonstrating breast cancer.

Saturation transfer in human red blood cells with normal and unstable hemoglobin

Saturation transfer phenomena from irradiated protein protons to observed water protons in packed human red blood cells (RBCs) with normal or unstable hemoglobin (Hb), i.e. Hb Yokohama and Hb Koeln, were studied using intermolecular cross-relaxation rates [CR; 1/T(IS)(H(2)O)], action spectra [[1-(I(infinity)/I(0))] vs f(2) (ppm), where I(0) and I(infinity) are the longitudinal magnetization of observed water protons before and after long-time f(2)-irradiation, respectively], CR spectra [CR vs f(2) (ppm)] and CR ratio vs f(2) (ppm) with f(2)-irradiation from -100 to 100 ppm at gammaH(2)/2pi of 69 or 250 Hz. RBCs (Hb Yokohama) exhibited many large Heinz bodies and strongly impaired filterability, while RBCs (Hb Koeln) showed few microscopically typical Heinz bodies and virtually normal filterability. However, increases in CR values for RBCs (Hb Koeln) and RBCs (Hb Yokohama), monitored by f(2)-irradiation below approximately -6 and above approximately 14 ppm, clearly indicated marked increases in association or aggregation of unstable Hb in RBCs compared with those in normal RBCs. CR values, monitored between approximately 0 and approximately 10 ppm, were related to not only association or aggregation of unstable Hb but also amounts of water in RBCs. Aggregation or association of unstable Hb exhibited greater effects on CR values compared with those of methemoglobin formation.

Two-dimensional near-IR correlation spectroscopy study of molten globule-like state of ovalbumin in acidic pH region: simultaneous changes in hydration and secondary structure

The molten globule-like states of ovalbumin (OVA) in acid aqueous solutions are investigated by generalized two-dimensional (2D) Fourier transform near-IR (FT-NIR) correlation spectroscopy. This new method allows us to explore the changes in hydration and the secondary structure simultaneously. FT-NIR spectra are measured for OVA aqueous solutions with concentrations of 1, 2, 3, 4, and 5 wt % over a pH range of 2.4-5.4. Concentration-perturbed 2D correlation spectra are calculated for the spectra in the 4850-4200 and 7500-5350 cm(-1) regions at different pH values. The 2D NIR synchronous spectrum in the 4850-4200 cm(-1) region shows a significant change upon going from pH 5.4 to 3.6. An autopeak at 4265 cm(-1) that is due to a combination of a symmetric CH(2) stretching mode and a CH(2) bending mode of side chains seen at pH 5.0 disappears completely in the synchronous spectrum at pH 3.6. This suggests that some amino acid residues of OVA are subjected to microenvironmental changes with decreasing pH. More remarkable changes are observed in the synchronous spectra at pHs below 2.8. A band near 4600 cm(-1) arising from a combination of amide B and amide II modes (amide B/II) shifts downward with considerable broadening between pH 3.0 and 2.4, suggesting that the strength of the hydrogen bonds of amide groups of OVA changes significantly. The synchronous and asynchronous spectra in the 4850-4200 cm(-1) region show that the intensities of the bands attributable to amide groups and side chains of OVA and that of the band near 4800 cm(-1) arising from water change in phase with the increase in the concentration above pH 2.8, but they vary out of phase below pH 2.8. The 2D synchronous map in the 7500-5350 cm(-1) region also shows marked changes upon going from pH 2.8 to 2.6. A broad autopeak at around 6950 cm(-1) assigned to free water and bound water with weak hydrogen bonds becomes very weak in the synchronous spectrum at pH 2.6, while broad autopeaks around 6450 cm(-1) suddenly appear that are due to bound water with several hydrogen bonds and the first overtone of an NH stretching mode of the amide groups of OVA. Therefore, it is very likely that protein hydration and the hydrogen bonds of amide groups change simultaneously in a narrow pH region of 2.8-2.6. It is probably that below pH 2.6 the protein assumes a molten globule-like state in which the whole molecule is very flexible, and side chains (but not the backbone chain) fluctuate significantly.

Equivalent cross-relaxation rate imaging in the synthetic copolymer gels and invasive ductal carcinomas of the breast

The values of equivalent cross-relaxation rate (ECR) correlated well with [i] water conditions in various copolymer gels and [ii] nature of malignant cells with regard to nuclear dysplasia and mitotic potential in breast carcinomas. The synthetic copolymer gels composed of any two or three monomers among 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA), N-vinyl-2-pyrrolidinone (N-VP), methyl methacrylate (MMA) and benzyl methacrylate (BMA). The ECR measurement was performed by using an off-resonance saturation pulse under conventional field-echo imaging at frequency within +/- 75 ppm apart from the water resonance frequency. The ECR values were readily to determine and non-time consuming parameter for cross relaxation rate. The ECR values at the frequency offset by 7-ppm (ECR-7) were divided the sample gels two classes, which must correspond to hydrophilic or hydrophobic ones. The sensitivity in the gels was nearly equivalent to the cross-relaxation rate itself. In the breast carcinomas, the ECR-7 correlates with the nature of malignant cells with regard to nuclear dysplasia and mitotic potential. The ECR-7 is better or more accurate than the STR-7 because the SDNRs between carcinoma and glandular tissue increased by approximately 50% on the ECR-7 compared with the STR-7. Thus the ECR values could be a new parameter for malignancy and cell proliferative activity of the breast carcinomas with non-invasive modalities by magnetic resonance imaging.

Basic studies on the equivalent cross-relaxation rate imaging (equivalent CRI)--phantom studies

We have studied saturation transfer in hydrophilic, cross-linked copolymer gels from irradiated polymer protons to observed water protons, using f2 (ppm) profiles of [1 - (I(infinity)/I(0))], [(I(0)/I(infinity)) - 1] or 1/T(IS)(H2O), where I(0) and I(infinity) are the longitudinal magnetization of the observed water protons before and after long-time-f2-irradiation on polymer protons, respectively, and 1/T(IS)(H2O) is the cross-relaxation rate. (A) [1 - (I(infinity)/I(0))] (magnetization transfer ratio, MTR) was used in magnetic resonance imaging (MRI) as the MTR imaging. 1/T(IS)(H2O) (cross-relaxation rate) was used in the imaging of the magnetization transfer rate constant. This method was quite time-consuming compared with MTR imaging. However, f2 (ppm) profiles of [(I(0)/I(infinity)) - 1] correlated well with corresponding profiles of 1/T(IS)(H2O), because [(I(0)/I(infinity)) - 1] is equal to 1/[T(IS)(H2O)/T1(H2O)]. These results lead us to the conclusion that [(I(0)/I(infinity)) - 1] might be applicable to cross-relaxation rate (CR)-like imaging, i.e. equivalent CRI. (B) W (%) (dry weight) profiles of [(I(0)/I(infinity)) - 1] and 1/T(IS)(H2O), obtained by near-resonance f2-irradiation, seem to indicate participation of molecular rigidity and an amount of bound water. However, those values, monitored with off-resonance f2-irradiation, seem to be independent of monomer composition and to indicate mainly participation of rigidity, i.e. W (%) of copolymer gels.

Viscosity analysis of the temperature dependence of the solution conformation of ovalbumin

The viscosity of ovalbumin aqueous solutions was studied as a function of temperature and of protein concentration. Viscosity-temperature dependence was discussed on the basis of the modified Arrhenius formula at temperatures ranging from 5 to 55 degrees C. The activation energy of viscous flow for hydrated and unhydrated ovalbumin was calculated. Viscosity-concentration dependence, in turn, was discussed on the basis of Mooney equation. It has been shown that the shape parameter S decreases with increasing temperature, and self-crowding factor K does not depend on temperature. At low concentration limit the numerical values of the intrinsic viscosity and of Huggins coefficient were calculated. A master curve relating the specific viscosity etasp to the reduced concentration c[eta], over the whole range of temperature, was obtained and the three ranges of concentrations: diluted, semi-diluted and concentrated, are discussed. It has been proved that the Mark-Houvink-Kuhn-Sakurada (MHKS) exponent for ovalbumin does not depend on temperature.

Saturation transfer ratio imaging in invasive ductal carcinomas of the breast

A prospective study was performed to investigate the correlations between saturation transfer ratio (STR) and histologic parameters of invasive ductal carcinomas in human breast. The histologic parameters investigated were the extent of fibrosis in the intercellular matrix, dysplastic changes of nuclei, and mitotic index. Twenty-seven patients with breast carcinoma were examined using an off-resonance saturation pulse in conjunction with conventional field-echo T(1)-weighted imaging at frequency offsets of 448 Hz and 1200 Hz from water resonance. The values of STR at frequency offset of 1200 Hz (STR(1200)) increased from non-scirrhous carcinoma to scirrhous carcinoma. Although STR(1200) showed correlation with the extent of fibrosis in the intercellular matrix (p<0.01, n = 27), they did not correlate with the dysplastic changes of nuclei or mitotic index. On the other hand, the values of STR at frequency offset of 448 Hz (STR(448)) demonstrated close correlation to dysplastic changes of nuclei and mitotic index (p<0.01, n = 27). STR(1200) correlates with the structural characteristics and STR(448) correlates with the nature of malignant cells with regard to nuclear dysplasia and mitotic potential.

1H-NMR and raman studies on perforating trauma-induced cataract formation in a mouse lens

In order to provide new insight into the molecular mechanism of perforating trauma-induced cataract formation in an 8-week-old ddY mouse lens, we performed an in situ investigation into changes in the water-protein and/or protein-protein interactions by using 500 MHz (1)H-NMR spectroscopy, and into structural alterations in lens proteins by using Raman spectroscopy. Cross-relaxation times of water protons in the perforated opaque lens were considerably shorter than those in the intact transparent lens, whereas there was no significant difference in water content, suggesting a drastic change in water-protein and protein-protein interactions in the perforated lens. In addition, there was no significant difference in the intensity ratios of several key Raman bands between intact and perforated lenses, indicating that no significant local and overall conformational changes in lens protein itself occur in the perforated lens. The present (1)H-NMR and Raman results lead us to the conclusion that changes leading to lens opacification in the perforating trauma-induced cataract appear to involve the rapid formation of immobile large lens protein aggregates without formation of intra- and intermolecular disulfide linkages, and rapid increase in a fraction of bound water associated with large protein aggregates.

Partially folded intermediates during trypsinogen denaturation

The equilibrium unfolding of bovine trypsinogen was studied by circular dichroism, differential spectra and size exclusion HPLC. The change in free energy of denaturation was delta GH2O = 6.99 +/- 1.40 kcal/mol for guanidine hydrochloride and delta GH2O = 6.37 +/- 0.57 kcal/mol for urea. Satisfactory fits of equilibrium unfolding transitions required a three-state model involving an intermediate in addition to the native and unfolded forms. Size exclusion HPLC allowed the detection of an intermediate population of trypsinogen whose Stokes radii varied from 24.1 +/- 0.4 A to 26.0 +/- 0.3 A for 1.5 M and 2.5 M guanidine hydrochloride, respectively. During urea denaturation, the range of Stokes radii varied from 23.9 +/- 0.3 A to 25.7 +/- 0.6 A for 4.0 M and 6.0 M urea, respectively. Maximal intrinsic fluorescence was observed at about 3.8 M urea with 8-aniline-1-naphthalene sulfonate (ANS) binding. These experimental data indicate that the unfolding of bovine trypsinogen is not a simple transition and suggest that the equilibrium intermediate population comprises one intermediate that may be characterized as a molten globule. To obtain further insight by studying intermediates representing different stages of unfolding, we hope to gain a better understanding of the complex interrelations between protein conformation and energetics.

H-NMR and CD studies on the structural transition of serum albumin in the acidic region--the N-->F transition

Helical content (f(alpha)) of bovine mercaptalbumin (BMA) showed the characteristic two-step decrease in the acidic region, one corresponding to the N-->F transition (pH 4.40-->3.75; f(alpha), 0.68-->0.58) and the other to the F-->E transition (the acid-expansion) (pH 3.60-->2.90; falpha, 0.58-->0.48). However, falpha of human serum albumin (HSA) mainly decreased in the N-->F transition (N-->F, pH 4.6-->3.4; falpha, 0.70-->-0.55 and F-->E, below pH 3.0; falpha, 0.55-->0.52). The difference in pH-profile of f(alpha) between BMA and HSA might be due to the microheterogeneity. The 1H-NMR spectra and cross-relaxation times (T(IS)) from irradiated to observed protein protons, which reflect the structural fluctuation and/or mobilability in proteins, were measured on the N-, F-, E-forms of HSA and BMA, and the N*-form (8.23 M urea, neutral pD) of iodoacetamide-blocked HSA (IA-HSA) and bovine serum albumin (IA-BSA). The 1H-NMR spectra and elongations of T(IS) values for the F- and E-forms of HSA and the E-form of BMA were quite similar to those for the N*-form of IA-HSA and IA-BSA, indicating the liberation of the intramolecular motion in the F- and E-forms. Those for the F-form of BMA were intermediate between the N- and E-form. The present results together with the reported data on hydrodynamic radii and D-H exchange reaction, indicate that the F-form of HSA and presumably BMA has a native-like globule form with a highly helical state and fluctuating tertiary structure. Thus, all of the present findings on the F-form of serum albumin seem to be in accord with the structural features for the F-form suggested by Foster's group (1-3, 19, 20, 22, 23) and the molten globule state demonstrated by Dolgikh et al. (40), and Ohgushi and Wada (36, 37).