Abstract P1-12-10: Regimen-specific rates of chemotherapy-related amenorrhea in breast cancer survivors

Background: Chemotherapy can damage the ovaries and cause amenorrhea, a surrogate for infertility. Young women often wish to understand and minimize their risk of chemotherapy-related amenorrhea (CRA). However, the incidence of CRA with regimens that do not include either an anthracycline or cyclophosphamide is poorly studied. For patients with HER-2 positive disease, these anthracycline and cyclophosphamide-sparing regimens (e.g., docetaxel-carboplatin) are common (in combination with Her-2 directed therapy) in both the neoadjuvant and adjuvant settings.

Methods: Women diagnosed with breast cancer under age 50 and within the past 10 years were recruited through a Dr. Susan Love Research Foundation Army of Women e-mail blast. Those who provided their contact information were mailed a consent form and medical record authorization form. Participants then received a web-based survey that inquired about receipt of and type of chemotherapy (including date of last dose) and date of last menstrual period (LMP). Patient-reported LMP was compared to date of final chemotherapy dose to determine if the LMP occurred before (defined as “CRA”) or after the last chemotherapy dose. When available, medical record data was used in place of survey data regarding type of chemotherapy used. Exclusion criteria included: LMP prior to diagnosis date, receipt of multiple chemotherapy regimens or no chemotherapy regimens, receipt of ovarian suppression medications (which interfere with interpretation of menstrual data), surgical menopause prior to or at the same time as diagnosis, a cancer diagnosis more than 10 years prior, incomplete menstrual data on the survey, report of an unknown chemotherapy regimen, and no date available for the last chemotherapy dose without an LMP within a month prior to survey completion. Fisher Exact test was used to compare CRA rates between regimens. Rates after two anthracycline-sparing regimens (taxane/cyclophosphamide; taxane/carboplatin) were compared to rates after anthracycline/cyclophosphamide/taxane.

Results: 273 women consented to participate in this study, 258 of whom filled out the web survey. 151 of them were eligible for this analysis with a median age at diagnosis of 41 (range 24-49) and a median time from last chemotherapy dose to survey of 62.5 months (range 2-138). CRA occurred in 51.2% of the 86 participants who received an anthracycline, cyclophosphamide, and a taxane, in 41.9% of the 43 participants who received only a taxane and cyclophosphamide (p=0.35), and in 13.3% of the 15 participants who received carboplatin with a taxane (p=0.01). When the 11 patients who were <12 months since last chemotherapy were excluded, CRA rates changed minimally. Age did not differ by regimen, but median time since chemotherapy was shorter in the taxane/carboplatin group (35 months vs. 68 months). Trastuzumab with or without pertuzumab was administered in 100% of patients who received carboplatin/taxane, in 23.3% of patients who received taxane and cyclophosphamide, and in 22.1% of patients who received anthracycline/cyclophosphamide/taxane.

Conclusions: This study suggests that carboplatin/taxane may be substantially less gonadotoxic than cyclophosphamide-based (neo)adjuvant regimens. Further research is necessary to confirm these findings.

Citation Format: Gast KC, Cathcart-Rake EJ, Norman A, Eshragi L, Obidegwu N, Yost K, Nichols HB, Rosenberg S, Su HI, Stewart E, Couch F, Vachon C, Ruddy KJ. Regimen-specific rates of chemotherapy-related amenorrhea in breast cancer survivors [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-12-10.

On the self-association potential of transmembrane tight junction proteins

Tight junctions seal intercellular clefts via membrane-related strands, hence, maintaining important organ functions. We investigated the self-association of strand-forming transmembrane tight junction proteins. The regulatory tight junction protein occludin was differently tagged and cotransfected in eucaryotic cells. These occludins colocalized within the plasma membrane of the same cell, coprecipitated and exhibited fluorescence resonance energy transfer. Differently tagged strand-forming claudin-5 also colocalized in the plasma membrane of the same cell and showed fluorescence resonance energy transfer. This demonstrates self-association in intact cells both of occludin and claudin-5 in one plasma membrane. In search of dimerizing regions of occludin, dimerization of its cytosolic C-terminal coiledcoil domain was identified. In claudin-5, the second extracellular loop was detected as a dimer. Since the transmembrane junctional adhesion molecule also is known to dimerize, the assumption that homodimerization of transmembrane tight junction proteins may serve as a common structural feature in tight junction assembly is supported.

Repräsentiert der HRCT-Emphysemindex die gesamte Lunge?

PURPOSE

: Comparison of emphysema index derived of thin section MD-CT of the entire lung volume and HRCT, simulated by calculation of every twentieth image of the whole data-set.

MATERIALS AND METHODS

Pulmonary emphysema was quantified by semiautomatic, segmentation of lung borders and assessment of lung volume and emphysema volume within these borders. The emphysema index (pixel index) was calculated. Statistical analysis was done by the sign-test and Bland-Altman-analysis.

RESULTS

Median lung volume, emphysema volume and emphysema index are significantly higher in simulated HRCT. Median lung volume (emphysema volume) calculated by HRCT is 5118 ml (407 ml) and 5040 ml (367 ml) calculated by the entire MD-CT data-set, representing differences of 1 and 8 % related to the median lung and emphysema volumes. Emphysema index is 0.09 (HRCT) and 0.08 (MD-CT).

CONCLUSION

HRCT overrates emphysema index compared to thin section MD-CT of the entire lung volume.

Effect of environmental conditions on aggregation and fibril formation of barstar

The dependence on environmental conditions of the assembly of barstar into amyloid fibrils was investigated starting from the nonnative, partially folded state at low pH (A-state). The kinetics of this process was monitored by CD spectroscopy and static and dynamic light scattering. The morphology of the fibrils was visualized by electron microscopy, while the existence of the typical cross-beta structure substantiated by solution X-ray scattering. At room temperature, barstar in the A-state is unable to form amyloid fibrils, instead amorphous aggregation is observed at high ionic strength. Further destabilization of the structure is required to transform the polypeptide chain into an ensemble of conformations capable of forming amyloid fibrils. At moderate ionic strength (75 mM NaCl), the onset and the rate of fibril formation can be sensitively tuned by increasing the temperature. Two types of fibrils can be detected differing in their morphology, length distribution and characteristic far UV CD spectrum. The formation of the different types depends on the particular environmental conditions. The sequence of conversion: A-state-->fibril type I-->fibril type II appears to be irreversible. The transition into fibrils is most effective when the protein chain fulfills particular requirements concerning secondary structure, structural flexibility and tendency to cluster.

Assembly of amyloid protofibrils via critical oligomers--a novel pathway of amyloid formation

The amyloid formation of phosphoglycerate kinase (PGK) was investigated by static and dynamic light-scattering. The time-course of the scattering intensity and the hydrodynamic radius scale with initial monomer concentration in a linear fashion over a range of about 50 in concentration. This sets limits on theories for aggregation kinetics that can be used, and points towards irreversible, cascade type models. In addition, circular dichroism (CD) was used to monitor the transition between a predominantly alpha-helical spectrum to a beta-sheet enriched one. The time-course of the CD also proves to scale linearly with initial monomer concentration. Electron microscopy shows that small oligomers as well as protofibrils are present during aggregation. The found coupling between growth of intermediates and acquisition of beta-sheet structure is interpreted in terms of a generalized diffusion-collision model, where stabilization of beta-strands takes place by intermolecular interactions.

3He-MRI-based vs. conventional determination of lung volumes in patients after unilateral lung transplantation: a new approach to regional spirometry

BACKGROUND

To use 3Helium (3He)-MRI in patients with unilateral lung grafts to assess the contributions of graft and native lung to total ventilated lung volume, and second to compare conventional measurements of intrapulmonary gas volume (spirometry, body plethysmography) with image-based volumetry of ventilated lung parenchyma visualized by hyperpolarized 3He-MRI.

METHODS

With Ethics Committee approval, five patients with single lung transplantation (SLTX) for idiopathic pulmonary fibrosis (IPF) underwent both conventional pulmonary function testing (PFT) and 3He-MRI of the lung. Intrapulmonary gas volume (GV) during the inspiratory breathhold for 3He-MRI was calculated from measured functional residual capacity (corrected for supine position) and inspired tidal volume. Image-based global and regional lung volumetries (LV) were performed in three-dimensionally reconstructed 3He-MR images (corrected for the fraction of tissue and blood).

RESULTS

Transplanted lungs were characterized by a homogeneous distribution of signal intensity, whereas the native lungs of the patients suffering from IPF displayed an inhomogeneous signal distribution pattern with numerous round or wedge-shaped ventilation defects. Total ventilated lung volume determined by 3He-MRI correlated well with PFT-based measurements, but with a systematic overestimation of the 3He-based lung volumetry of approximately 20%. Functioning lung grafts contributed 66+/-6% and their corresponding native IPF lungs 34+/-6% to total ventilated volume (P<0.05; mean+/-SD).

CONCLUSION

3Helium-MRI of the lung offers a novel approach to regional determination of ventilated lung volume, including its blood and tissue compartments. The advantage of this technique over computed tomography or ventilation scintigraphy is the lack of radiation exposure, and hence its repeatability. Follow up of SLTX patients with this new technique may allow the monitoring of functional and structural developments of grafted lungs with better sensitivity and specificity than PFT.

[Dynamic imaging of the nasal cavity and the paranasal sinuses with polarized 3helium MRI]

PURPOSE

Reduced or blocked ventilation of the paranasal sinuses is probably the most important factor in the development of sinusitis. Recently, the use of optically polarized noble gas isotopes has attracted increasing interest for use in a variety of promising MR applications. The aim of this study was to test the feasibility of imaging and visualization ventilation of the nasal cavity and paranasal sinus in MR by inhalation of hyperpolarized (3)helium. The goal was to evaluate ventilation defects of the paranasal sinuses.

VOLUNTEERS AND METHODS

Three volunteers were enrolled in the study. (3)Helium was polarized to 40 - 50 % by direct optical pumping. 300 ml of 100 % (3)helium were administered in the left nasal vestibule through a glass tube. With a closed contralateral nasal vestibule, the Valsalva maneuver was performed twice. Using a dedicated application unit, which is also used in MR imaging of the lung, an exact amount of (3)helium gas was administered at the beginning of inspiration. Measurements were carried out on a clinical 1.5 T scanner. Coronal images of the nasal cavity and paranasal sinuses were acquired using ultrafast gradient-echo pulse sequence (TR = 2 ms, TE = 0.7 ms, FA < 2 degrees, 75 x 128, FOV = 500) with an image aquisition time of 130 ms.

RESULTS

The oral cavity and nasal cavities display a very high signal intensity after inhalation of polarized (3)helium gas. The signal intensity in the left maxillary sinus was higher compared to the right one. The mean signal intensity on the left side was 526 +/- 86 and on the right side 336 +/- 102. The left and right frontal sinus and ethmoid sinus only show signal of hyperpolarized (3)helium after two Valsalva maneuvers. Because of the low signal intensity of the frontal and ethmoid cells their visualization was incomplete. The signal to noise ratio was 14.1 for the left maxillary sinus, 8.9 for the right side, 6.3 for the left ethmoid sinus, 5.8 for the right side and 6.6 for the left frontal sinus and 7.8 for the right side.

CONCLUSION

(3)Helium MR allows imaging of the nasal cavity and the paranasal sinuses. Perhaps this method could be a new tool to visualize the ventilation of the maxillary sinus without ionizing radiation. Interpretations about the ventilation of the frontal and ethmoid cells remain speculative.

Fluoroalcohol-induced structural changes of proteins: some aspects of cosolvent-protein interactions

The conformational transitions of bovine beta-lactoglobulin A and phosphoglycerate kinase from yeast induced by hexafluoroisopropanol (HFIP) and trifluoroethanol (TFE) have been studied by dynamic light scattering and circular dichroism spectroscopy in order to elucidate the potential of fluoroalcohols to bring about structural changes of proteins. Moreover, pure fluoroalcohol-water mixed solvents were investigated to prove the relation between cluster formation and the effects on proteins. The results demonstrate that cluster formation is mostly an accompanying phenomenon because important structural changes of the proteins occur well below the critical concentration of fluoroalcohol at which the formation of clusters sets in. According to our light scattering experiments, the remarkable potential of HFIP is a consequence of extensive preferential binding. Surprisingly, preferential binding seems to play a vanishing role in the case of TFE. However, the comparable Stokes radii of both proteins in the highly helical state induced by either HFIP or TFE point to a similar degree of solvation in both mixed solvents. This shows that direct binding or an indirect mechanism must be equally taken into consideration to explain the effects of alcohols on proteins. The existence of a compact helical intermediate with non-native secondary structure on the transition of beta-lactoglobulin A from the native to the highly helical state is clearly demonstrated.

Study of the conformational transition of A beta(1-42) using D-amino acid replacement analogues

A critical event in Alzheimer's disease is the transition of Abeta peptides from their soluble forms into disease-associated beta-sheet-rich conformers. Structural analysis of a complete D-amino acid replacement set of Abeta(1-42) enabled us to localize in the full-length 42-mer peptide the region responsible for the conformational switch into a beta-sheet structure. Although NMR spectroscopy of trifluoroethanol-stabilized monomeric Abeta(1-42) delineated two separated helical domains, only the destabilization of helix I, comprising residues 11-24, caused a transition to a beta-sheet structure. This conformational alpha-to-beta switch was directly accompanied by an aggregation process leading to the formation of amyloid fibrils.

Conversion of yeast phosphoglycerate kinase into amyloid-like structure

Yeast phosphoglycerate kinase is a structurally well-characterized enzyme consisting of 415 amino acids without disulfide bonds. Anion-induced refolding from its acid-unfolded state gives rise to the formation of worm-like amyloid fibrils with a persistence length of 73 nm. Electron microscopy and small-angle X-ray scattering data indicate that the fibrils have an elliptical cross-section with dimensions of 10.2 nm x 5.1 nm. About half of all amino acids are organized in form of cross-beta structure which gives rise to typical infrared spectra, X-ray diffraction and yellow-green birefringence after Congo red staining. The kinetics of amyloid formation, monitored by infrared spectroscopy, dynamic light scattering and X-ray scattering, was found to be strongly dependent on protein concentration. The infrared data indicate that the formation of cross-beta structure practically comes to an end already after some hours, whereas the length-growth of the amyloid fibrils, monitored by small-angle X-ray scattering, was not yet completed after 1,300 hours.

Proteins can adopt totally different folded conformations

The three-dimensional structure of a protein is determined by interactions between its amino acids and by interactions of the amino acids with molecules of the environment. The great influence of the latter interactions is demonstrated for the enzyme phosphoglycerate kinase from yeast (PGK). In the native state, PGK is a compact, bilobal molecule; 35% and 13% of its amino acids are organised in the form of alpha-helices and beta-sheets, respectively. The molecules unfold at acidic pH and low ionic strength forming random-walk structures with a persistence length of 3 nm. More than 90% of the amino acid residues of the ensemble have phi,psi-angles corresponding to those of a straight beta-chain. Upon addition of 50% (v/v) trifluoroethanol to the acid-unfolded protein, the entire molecule is transformed into a rod-like, flexible alpha-helix. Addition of anions, such as chloride or trichloroacetate, to the acid-unfolded protein leads to the formation of amyloid-like fibres over a period of many hours when the anion concentration exceeds a critical limit. Half of the amino acid residues are then organised in beta-sheets. Both of the non-natively folded states of PGK contain more regular secondary structure than the native one. The misfolding starts in both cases from the acid-unfolded state, in which the molecules are essentially more expanded than in other denatured states, e.g. those effected by temperature or guanidine hydrochloride.

Secondary structure and oligomerization behavior of equilibrium unfolding intermediates of the lambda cro repressor

The thermal unfolding of the wild-type Cro repressor, its disulfide-bridged mutant Cro-V55C (with the Val-55 --> Cys single amino acid substitution), and a CNBr-fragment (13-66)2 of Cro-V55C was studied by Fourier transform infrared spectroscopy and dynamic light scattering. The combined approach reveals that thermal denaturation of Cro-WT and Cro-V55C proceeds in two steps through equilibrium unfolding intermediates. The first thermal transition of the Cro-V55C dimer involves the melting of the alpha-helices and the short beta-strand localized in the N-terminal part of the molecule. This event is accompanied by the formation of tetramers, and also impacts on the hydrogen-bonding interactions of the C-terminal beta-strands. The beta-sheet formed by the C-terminal parts of each polypeptide chain is the major structural feature of the intermediate state of Cro-V55C and unfolds during a second thermal transition, which is accompanied by the dissociation of the tetramers. Cutting of 12 amino acids in the N-terminal region is sufficient to prevent the formation of alpha-helical structure in the CNBr-fragment of Cro-V55C, and to induce tetramerization already at room temperature. The tetramers may persist over a broad temperature range, and start to dissociate only upon thermal unfolding of the beta-sheet structure formed by the C-terminal regions. The wild-type protein is a dimer at room temperature and at protein concentrations of 1.8-5.8 mg/mL. At lower concentrations, the dimers are stable until the onset of thermal unfolding, which is accompanied by the dissociation of the dimers into monomers. At higher protein concentrations, the unfolding is more complex and involves the formation of tetramers at intermediate temperatures. At these intermediate temperatures, the Cro-WT has lost all of its alpha-helical structure and also most of its native beta-sheet structure. Upon further temperature increase, a tendency for an intermolecular association of the beta-strands is observed, which may result in irreversible beta-aggregation at high protein concentrations.

Trifluoroethanol-induced conformational transitions of proteins: insights gained from the differences between alpha-lactalbumin and ribonuclease A

The trifluoroethanol (TFE)-induced structural changes of two proteins widely used in folding experiments, bovine alpha-lactalbumin, and bovine pancreatic ribonuclease A, have been investigated. The experiments were performed using circular dichroism spectroscopy in the far- and near-UV region to monitor changes in the secondary and tertiary structures, respectively, and dynamic light scattering to measure the hydrodynamic dimensions and the intermolecular interactions of the proteins in different conformational states. Both proteins behave rather differently under the influence of TFE: alpha-lactalbumin exhibits a molten globule state at low TFE concentrations before it reaches the so-called TFE state, whereas ribonuclease A is directly transformed into the TFE state at TFE concentrations above 40% (v/v). The properties of the TFE-induced states are compared with those of equilibrium and kinetic intermediate states known from previous work to rationalize the use of TFE in yielding information about the folding of proteins. Additionally, we report on the properties of TFE/water and TFE/buffer mixtures derived from dynamic light scattering investigations under conditions used in our experiments.

Compactness of the kinetic molten globule of bovine alpha-lactalbumin: a dynamic light scattering study

During folding of globular proteins, the molten globule state was observed as an equilibrium intermediate under mildly denaturing conditions as well as a transient intermediate in kinetic refolding experiments. While the high compactness of the equilibrium intermediate of alpha-lactalbumin has been verified, direct measurements of the compactness of the kinetic intermediate have not been reported until now. Our dynamic light scattering measurements provide a complete set of the hydrodynamic dimensions of bovine alpha-lactalbumin in different conformational states, particularly in the kinetic molten globule state. The Stokes radii for the native, kinetic molten globule, equilibrium molten globule, and unfolded states are 1.91, 1.99, 2.08, and 2.46 nm, respectively. Therefore, the kinetic intermediate appears to be even more compact than its equilibrium counterpart. Remarkable differences in the concentration dependence of the Stokes radius exist revealing strong attractive but repulsive intermolecular interactions in the kinetic and equilibrium molten globule states, respectively. This underlines the importance of extrapolation to zero protein concentration in measurements of the molecular compactness.

Initial hydrophobic collapse is not necessary for folding RNase A

BACKGROUND

One of the main distinctions between different theories describing protein folding is the predicted sequence of secondary structure formation and compaction during the folding process. Whether secondary structure formation precedes compaction of the protein molecules or secondary structure formation is driven by a hydrophobic collapse cannot be decided unequivocally on the basis of existing experimental data.

RESULTS

In this study, we investigate the refolding of chemically denatured, disulfide-intact ribonuclease A (RNase A) by monitoring compaction and secondary structure formation using stopped-flow dynamic light scattering and stopped-flow CD, respectively. Our data reveal the formation of a considerable amount of secondary structure early in the refolding of the slow folding species of RNase A without a significant compaction of the molecules. A simultaneous formation of secondary structure and compaction is observed in the subsequent rate-limiting step of folding.

CONCLUSIONS

During folding of RNase A an initial global hydrophobicity is not observed, which contradicts the view that this is a general requirement for protein folding. This folding behavior could be typical of similar, moderately hydrophobic proteins.

Pulmonary nodules: detection with low-dose vs conventional-dose spiral CT

The purpose of the study was the evaluation of low-dose spiral CT in the detection and assessment of contours of pulmonary nodules. In a prospective investigation 71 consecutive chest CT examinations were acquired both at 30 and 200 mA. Films were interpreted independently by two radiologists. According to the size, nodules were divided into four categories: </= 3, 4-5, 6-10, and > 10 mm; nodule shape was registered. With both protocols, 240 nodules were detected. The correlation coefficient for both methods was 0.89. Discrepancies were found most frequently in nodules near to pulmonary vessels. Nodule size estimation did not differ more than one size category. Eight spiculated nodules were identified by both techniques. Low-dose spiral CT of the chest has a high sensitivity in the detection of pulmonary nodules. If clinical circumstances require dose minimization, low-dose spiral CT may be advocated as an alternative screening method to conventional dose spiral CT.

Folding of firefly (Photinus pyralis) luciferase: aggregation and reactivation of unfolding intermediates

The guanidine-induced unfolding of firefly (Photinus pyralis) luciferase involves two inactive equilibrium intermediates and is freely reversible at low protein concentration and low temperature. However, reactivation is exceedingly slow so that the equilibrium is attained only after several days of incubation and reactivation yields decrease strongly with increasing protein concentration, suggesting that aggregation is a competing side reaction [Herbst et al. (1997) J. Biol. Chem. 272, 7099-7105]. We investigated the role of the equilibrium intermediates in the aggregation process using size-exclusion chromatography and dynamic light scattering to monitor their association state. Although the more unfolded intermediate aggregated much more rapidly, both intermediates associated irreversibly without a conformational change visible by fluorescence or circular dichroism, forming small oligomers which remained soluble in the presence of the denaturant. The association kinetics are compatible with a nucleated polymerization mechanism. Unfolding kinetics at 1 M denaturant indicated the presence of a further inactive intermediate capable to reactivate rapidly with kinetics similar to those observed for luciferase reactivation in the presence of cell extracts. The data suggest a kinetic trap in luciferase refolding that is accessible from both equilibrium intermediate conformations and is avoided in the presence of molecular chaperones.

Denatured states of yeast phosphoglycerate kinase

Structures of proteins in unfolded states have important implications for the protein folding problem and for the translocation of polypeptide chains. Acid-denatured, cold-denatured, and 6 M guanidine hydrochloride (GuHCl) denatured yeast phosphoglycerate kinase (PGK) are ensembles of flexible unfolded molecules with rapidly interconverting structures of the individual polypeptide chains. They differ, however, in their physical properties, such as in coil size and in stiffness over a short distance along the chain. These properties of polypeptide chains can be described well by persistence statistics. A solution containing 0.7 M GuHCl at 4.5 degrees C is nearly a Theta-solvent for PGK. By contrast, 6 M GuHCl is a good solvent for PGK. Acid-denatured PGK at low ionic strength has the most expanded and stiffest chains. The conformation of heat-denatured PGK should be more compact than that of random walk chains at the Theta-point, as can be inferred from measurements on other proteins. Investigations of heat-denatured PGK by scattering methods are unfeasible due to aggregation of the protein. The persistence length as a measure of chain stiffness varies between a = 1.74 nm for cold-denatured PGK and a = 3.0 nm for acid-denatured PGK. The distribution functions of the gyration radii were calculated from the X-ray scattering data for all unfolded states and compared with the radius of gyration of the natively folded molecule.

Lack of coupling between secondary structure formation and collapse in a model polypeptide that mimics early folding intermediates, the F2 fragment of the Escherichia coli tryptophan-synthase beta chain

The isolated, 101-residue long C-terminal (so called F2) fragment of the beta chain from Escherichia coli tryptophan synthase was shown previously to fold into an ensemble of conformations that are condensed, to contain large amounts of highly dynamic secondary structures, and to behave as a good model of structured intermediates that form at the very early stages of protein folding. Here, solvent perturbations were used to investigate the forces that are involved in stabilizing the secondary structure (monitored by far-UV CD) and the condensation of the polypeptide chain (monitored by dynamic light scattering) in isolated F2. It was observed that neither the ionic strength, nor the pH (between 7 and 10), nor salts of the Hofmeister series affected the global secondary structure contents of F2, whereas some of these salts affected the collapse slightly. Addition of trifluoroethanol resulted in a large increase in both the amount of secondary structure and the Stokes radius of F2. Conversely, F2 became more condensed upon raising the temperature from 4 to 60 degrees C, whereas in this temperature range, the secondary structure undergoes significant melting. These observations lead to the conclusion that, in isolated F2, there is no coupling between the hydrophobic collapse and the secondary structure. This finding will be discussed in terms of early events in protein folding.

Conformation of thermally denatured RNase T1 with intact disulfide bonds: a study by small-angle X-ray scattering

Small-angle X-ray scattering of RNase T1 with intact disulfide bonds was measured at 20 degrees and 60 degrees C in order to get insight into the structural changes of the protein caused by thermal denaturation. The radius of gyration increases from R(G)= 1.43 nm to R(G) = 2.21 nm. The conformations of the molecules at 60 degrees C are similar to those of ring-shaped random walk chains. However, the molecules are more compact than one would expect under theta conditions due to attractive interactions between the chain segments. The volume needed for free rotation of the thermally unfolded protein molecules about any axis in solution is five times greater than in the native state whereas the hydrodynamic effective volume is increasing only two times.

Ribonuclease T1 has different dimensions in the thermally and chemically denatured states: a dynamic light scattering study

Ribonuclease T1 can be unfolded and refolded without forming noticeable amounts of aggregates allowing to characterise the dimensions of a protein in different denatured states in terms of the Stokes radius RS. Upon thermal unfolding RS increases from 1.74 nm at 20 degrees C to 2.14 nm at 60 degrees C. By contrast, RS = 2.40 nm was obtained at 5.3 M guanidinium chloride (GuHCl) and 20 degrees C. Heating from 20 degrees C to 70 degrees C in the presence of 5.3 M GuHCl led to a 5% decrease in RS.

Conformational differences of ovine and human corticotropin releasing hormone. A CD, IR, NMR and dynamic light scattering study

The differences in the conformational properties of ovine (o) and human (h) CRH in aqueous solution, structure-inducing TFE and in the presence of detergent micelles and lipid vesicles have been investigated by circular dichroism, Fourier transform infrared spectroscopy, NMR and dynamic light scattering. o-CRH was found to exist as a monomer with little regular structure in dilute aqueous solution. Association at concentrations higher than 10-3 mol/L results predominantly in dimers. The induction of a substantial amount of intermolecular beta-structure seems to be the result of interactions of the C-terminal hexapeptide and the N-terminal region 6-12 of o-CRH chains in antiparallel orientation. In contrast, h-CRH exhibits a high tendency of association which is highly sensitive to the pH. The formation of tetramers at millimolar peptide concentration is related to a helical content of ca. 50%. The potentially helical, highly hydrophobic region 6-20 enlarged by more hydrophobic residues in position 23 and 25 is proposed to stabilize the h-CRH associates. In the presence of structure inducing TFE (> 40% v) both CRH peptides exist as monomers. o-CRH reveals about 72% helicity, in h-CRH the formation of about 85% helix is observed. The differences in helicity of the two CRH molecules are located in the C-terminal heptapeptide, as concluded on the basis of NMR studies. Both peptides bind to detergent micelles at pH 4 as well as 7.4 associated with an increase in the alpha-helical content. Interaction of the two peptides with DMPC vesicles was found exclusively at pH 4. Above the phase transition temperature of DMPC the alpha-helical content in h-CRH increases slightly; however, o-CRH reveals a substantial amount of beta-type structure. The intramolecular type of beta-structure is associated with a deeper insertion of the o-CRH region 6-12 into the hydrophobic region of the lipid bilayer, whereas the corresponding region of h-CRH is kept in the bilayer surface. The higher helicity of h-CRH might explain to some extent its higher affinity to the CRH receptor, CRH antibodies and the CRH binding protein.

Reduced-denatured ribonuclease A is not in a compact state

Dynamic light scattering and circular dichroism experiments were performed to determine the compactness and residual secondary structure of reduced and by 6 M guanidine hydrochloride denatured ribonuclease A. We find that reduction of the four disulphide bonds by dithiothreitol at 20 degrees C leads to total unfolding and that a temperature increase has no further effect on the dimension. The Stokes' radius of ribonuclease A at 20 degrees C is R(s) = (1.90 +/- 0.04) nm (native) and R(s) = (3.14 +/- 0.06) nm (reduced-denatured). Furthermore, circular dichroism spectra do not indicate any residual secondary structure. We suggest that reduced-denatured Ribonuclease A has a random coil-like conformation and is not in a compact denatured state.

Prothymosin alpha: a biologically active protein with random coil conformation

Prothymosin is an acidic protein with an unusual amino acid composition. Though its exact function is not yet known, its high evolutionary conservation and wide tissue distribution suggest an essential biological role. Its physical state, which is controversially discussed in previous publications, was investigated using small-angle X-ray scattering, dynamic light scattering, mass spectrometry, and circular dichroism (CD). Our results unequivocally demonstrate that prothymosin is a monomer under physiological conditions. The protein adopts a random coillike conformation but exhibits persistence of direction and curvature. No regular secondary structure is detectable by CD. The Stokes radius, Rs = 3.07 nm, and the radius of gyration, RG = 4.76 nm, are 1.77 and 3.42 times larger, respectively, than those expected for a compactly folded protein consisting of 109 amino acid residues. A remarkable amount of secondary structure is formed only in the presence of trifluoroethanol at low pH. The finding that a biologically active protein molecule with 109 amino acid residues adopts a random coil conformation under physiological conditions raises the question whether this is a rare or a hitherto-overlooked but widespread phenomenon in the field of macromolecular polypeptides.

Cold denaturation of yeast phosphoglycerate kinase: which domain is more stable?

Under destabilising conditions both heat and cold denaturation of yeast phosphoglycerate kinase (PGK) can be observed. According to previous interpretation of experimental data and theoretical calculations, the C-terminal domain should be more stable than the N-terminal domain at all temperatures. We report on thermal unfolding experiments with PGK and its isolated domains, which give rise to a revision of this view. While the C-terminal domain is indeed the more stable one on heating, it reveals lower stability in the cold. These findings are of importance, because PGK has been frequently used as a model for protein folding and mutual domain interactions.

Compactness of protein molten globules: temperature-induced structural changes of the apomyoglobin folding intermediate

Apomyoglobin undergoes a two-step unfolding transition when the pH is lowered from 6 to 2. The partly folded intermediate (I) state at pH 4 and low ionic strength has properties of a molten globule. We have studied structural features of this state, its compactness, content of secondary structure, and specific packing of aromatic side chains, using dynamic light scattering, and small-angle X-ray scattering and far- and near-ultraviolet circular dichroism spectroscopy. Particular attention was paid to temperature-dependent structural changes. The results are discussed with reference to the native-like (N) state and the highly unfolded (U) state. It turned out that the I-state is most compact near 30 degrees C, having a Stokes radius 20% larger and a radius of gyration 30% larger than those of the N-state. Both cooling and heating relative to 30 degrees C led to an expansion of the molecule, but the structural changes at low and high temperatures were of a different kind. At temperatures above 40 degrees C non co-operative melting of structural elements was observed, while the secondary structure was essentially retained on cooling. The results are discussed in context with theoretical predictions of the compactness and the stability of apomyoglobin by Alonso et al. [Alonso, D. O. V., Dill, K. A., and Stigter, D. (1991) Biopolymers 31:1631-1649]. Comparing the I-state of apomyoglobin with the molten globules of alpha-lactalbumin and cytochrome c, we found that the compactness of the molten globule states of the three proteins decreases in the order alpha-lactalbumin > apocytochrome c > apomyoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

The thermostability of natural variants of bacterial plasminogen-activator staphylokinase

Three natural variants (wild-type staphylokinase, [R36G, R43H]staphylokinase, and [G34S, R36G, R43H]staphylokinase) of the bacterial plasminogen-activator staphylokinase, a 136-amino-acid protein secreted by certain Staphylococcus aureus strains, have been characterized. These variants differ at amino acid positions 34, 36 and 43 only, and have a very similar plasminogen-activating capacity and conformation in solution, as revealed by fluorescence spectroscopy, dynamic light scattering and circular dichroism. However, the thermostability of these variants is significantly different. At 70 degrees C and 0.5 mg protein/ml, irreversible inactivation occurred with apparent half-life (t1/2) values 0.54 +/- 0.13, 0.81 +/- 0.20 and 3.7 +/- 0.7 h (mean +/- SEM) for wild-type staphylokinase, [R36G, R43H]staphylokinase, and [G34S, R36G, R43H]staphylokinase, respectively, with corresponding values at 0.08 mg/ml of 5.3 +/- 1.4 h and 11 +/- 2.0 h for wild-type staphylokinase and [R36G, R43H]staphylokinase, respectively. Dynamic light-scattering measurements indicated that inactivation was associated with protein aggregation, which precluded accurate determination of transition temperatures and enthalpies of unfolding. 0.08-0.34 mg/ml [G34S, R36G, R43H]staphylokinase, however, did not aggregate at 70 degrees C but underwent unfolding as revealed by a 20% increase in the Stokes' radius and a 30% decrease in circular dichroism. The unfolding was reversible upon cooling and was associated with full recovery of functional activity. Thus, these natural variants of staphylokinase have a different sensitivity to thermal inactivation, that is mediated by reversible unfolding of the protein and concentration-dependent irreversible aggregation. [G34S, R36G, R43H]staphylokinase, the most resistant natural variant, has a stability approaching the minimal requirements for pasteurization, which would facilitate its development for clinical use.

Cold denaturation-induced conformational changes in phosphoglycerate kinase from yeast

The temperature-dependent conformational equilibrium of 3-phosphoglycerate kinase has been studied in the temperature range from 1 to 30 degrees C by means of dynamic light scattering, small-angle X-ray scattering, differential scanning calorimetry, circular dichroism spectroscopy, and fluorescence spectroscopy. At 28 degrees C and in the presence of 0.7 M guanidine hydrochloride (GuHCl), the radius of gyration (RG) and the Stokes radius (RS) are 2.44 and 3.09 nm, respectively. Decreasing the temperature effects unfolding of the molecule, a process that involves two stages. The two stages correspond to the successive unfolding of the N-terminal and C-terminal domains. The peak maxima of the excess heat capacity, determined from differential calorimetric scans, extrapolated to 0 scan rate, are positioned at 16.5 degrees C for the N-terminal domain and at 6.3 degrees C for the C-terminal domain. At 4.5 degrees C, the radius of gyration and the Stokes radius increase to 7.8 and 4.8 nm, respectively. The persistence length and the length of the statistical chain segment of the unfolded polypeptide chain are 1.74 and 3.48 nm, corresponding to five and ten amino acids, respectively. At 1 degrees C, the dimensions of the unfolded chain nearly agree with the predicted dimensions under theta conditions. Thus, the conformational changes upon cold denaturation can be described by a transition from a compactly folded molecule to a random coil. The conformation-dependent ratio rho = RGRS-1 increases from rho = 0.79 to rho = 1.63. The volume of the unfolded chain is 30 times larger than that of the folded chain in the native state.(ABSTRACT TRUNCATED AT 250 WORDS)

Cold denaturation of yeast phosphoglycerate kinase: kinetics of changes in secondary structure and compactness on unfolding and refolding

Under mildly destabilizing conditions (0.7 M GuHCl), phosphoglycerate kinase from yeast undergoes a reversible two-step equilibrium unfolding transition when the temperature is lowered from 30 to 1 degree C (Griko, Y. V., Venyaminov, S. Y., & Privalov, P. L. (1989) FEBS Lett. 244, 276-278). The kinetics of the changes in compactness and secondary structure have been studied by means of dynamic light scattering and far-UV circular dichroism, respectively. It turned out that unfolding and refolding after an appropriate temperature jump (T-jump) was performed proceeded in substantially different ways. After a T-jump from 30 to 1 degree C, a multiphasic unfolding behavior was observed, reflecting the independent unfolding of the N-terminal and C-terminal domains with time constants of about 7 and 45 min, respectively. A remarkable feature of the unfolding process is the simultaneous change of compactness and secondary structure. Refolding after a T-jump from 1 degree C to higher temperatures occurs in two stages. At the first stage an appreciable amount of secondary structure is formed rapidly within the dead time of the T-jump, while the overall dimensions of the polypeptide chain remain essentially unchanged. Thus, an extended folding intermediate is formed at an early stage of folding. Further information of secondary structure proceeds slowly within a time range of minutes in parallel with the increase of compactness. At 30 degrees C, both domains refold simultaneously, while at 15 degrees C, independent folding can be observed. These findings are discussed with respect to predictions of existing models of folding.

Physical and conformational properties of staphylokinase in solution

The structure of staphylokinase has been analyzed by solution X-ray scattering, dynamic light scattering, ultracentrifugation and ultraviolet circular dichroism spectroscopy. Staphylokinase has a radius of gyration of 2.3 nm, a Stokes radius of 2.12 nm and a maximum dimension of 10 nm. The sedimentation coefficient is 1.71 S. These physical parameters indicate that the shape of staphylokinase is very elongated. The protein molecule consists of two folded domains of similar size. The mean distance of the centres of gravity of the domains is 3.7 nm. The mutual positions of the two domains are variable in solution. Thus, the molecule is shaped like a flexible dumbbell. About 18% of the amino acids of staphylokinase are organized in helical structures, 30% are incorporated in beta-sheets and 20% form turns.

Application of dynamic light scattering to studies of protein folding kinetics

The applicability of dynamic light scattering to studies of the kinetics of unfolding and refolding reactions of proteins is discussed and demonstrated experimentally. The experimental set-up and the data acquisition and data evaluation schemes that have been optimized for kinetic experiments are described. The relationship of the signal-to-noise ratio to the minimum data acquisition time that is needed to obtain results of sufficiently high precision is discussed. It turns out that the attainable time resolution is of the order of a few seconds for proteins with molar masses of about 50,000 g.mol(-1) and concentrations of 1 g.1(-1). Thus, DLS is too slow to follow conformational changes in the subsecond region, but it is useful for studies of unfolding-refolding reactions of proteins that proceed with time constants in the range of seconds or minutes. This is demonstrated by investigations of the kinetics of the cold denaturation of 3-phosphoglycerate kinase from yeast.

Streptokinase is a flexible multi-domain protein

The structure of streptokinase in solution has been studied by dynamic light scattering, small-angle X-ray scattering and circular dichroism spectroscopy. The Stokes' radius and radius of gyration of the protein monomer are 3.58 nm and 4.03 nm, respectively. The maximum intraparticle distance of the molecule is 14 nm. More than half of the amino acids of the molecule are organized in regular secondary structures. The X-ray scattering curve, the results from dynamic light scattering, and the finding that at least 50% of the amino acid residues are organized in regularly folded secondary structures are consistent with the following structural model. Streptokinase consists of four compact, separately folded, domains linked by mobile segments of the protein chain. The molecule exhibits the conformation of a flexible string-of-beads in solution.

Solvent dependence of dimensions of unfolded protein chains

The radii of gyration of unfolded apo-cytochrome C at pH 2.3 have been determined in three conditions: (i) 20 mM sodium phosphate buffer; (ii) 0.25 M NaCl; and (iii) 6.65 M GuHCl by small-angle X-ray scattering, and (iii) from translational diffusion coefficients measured by dynamic light scattering. The radius of gyration of the unfolded protein chain depends remarkably on the quality of the solvent, decreasing in the order 20 mM sodium phosphate greater than 6.65 M GuHCl greater than 0.25 M NaCl. The value of the radius of gyration in 0.25 M NaCl and also the value estimated for infinite ionic strength are close to the value predicted theoretically for the theta-point. This means that water in the absence of electrostatic interactions is a poor solvent for an unfolded protein while 6.65 M GuHCl is a better solvent.

Acid denatured apo-cytochrome c is a random coil: evidence from small-angle X-ray scattering and dynamic light scattering

The conformation of a denatured protein has been investigated, since the experimental data on the structure of denatured proteins have been incomplete until now. The Stokes' radius Rs and the radius of gyration Rg of apo-cytochrome c at pH 2.3 have been determined by dynamic light scattering and small-angle X-ray scattering, respectively. The values of these structure parameters, extrapolated to zero protein concentration, are Rs = 3.0 nm and Rg = 4.6 nm. The ratio Rg.Rs-1 is a sensitive indicator of the molecular conformation. The ratio of 1.55 obtained by us is typical for a random-coil polymer. The persistence length--the characteristic of the molecular flexibility--was determined to be a = 1.81 nm. From this results the root-mean-square average end-to-end distance of the molecules [h2] 1/2 = 11.2 nm and the characteristic ratio [h2]/npl2p = 8.43, where np = 104 is the number of amino acid residues and lp the distance between C alpha-atoms. We obtained a second virial coefficient A2 = 8.2.10(-3) mol cm3 g-2. The experimentally determined structure parameters are in approximate agreement with those predicted by Flory and others for an unperturbed, randomly coiled polypeptide. The expansion factor lies between 1.1 and 1.2. In conclusion, we have shown that apo-cytochrome c at pH 2.3 and at low concentrations has the conformation of a perturbed random coil with repulsive potentials between the chain segments.

Changes of the oligomeric structure of legumin from pea (Pisum sativum L.) after succinylation

The influence of various levels of succinylation on the structure of the legumin from pea seed has been studied by the techniques of sedimentation velocity, viscometry, fluorescence and circular dichroism spectroscopy, as well as dynamic light scattering. The protein dissociates gradually into the 3S subunit forming a 7S intermediate. At a level of 75-80% succinylation, sudden unfolding of the protein occurs characterized by drastic changes in viscometric and spectroscopic properties. The fluorescence spectra point to the formation of a novel organized structure at a moderate degree of modification before the molecular unfolding takes place. The succinylated subunit was shown to have a sedimentation coefficient of 3.2S, a diffusion coefficient of 5.03 x 10(-7) cm2 . s-1 a Stokes' radius of 4.24 nm, a partial specific volume of 0.703 ml/g, an intrinsic viscosity of 0.13 dl/g, a molar mass of 52.2 kDa and a frictional ratio of 1.74.

Insulin aggregation in solution

The process of insulin aggregation in neutral solutions was studied by dynamic light scattering. Solutions of different concentrations were subjected to thermal and mechanical stress (37 degrees, rotation) for a period of 4 weeks. The starting solutions contained exclusively one particle distribution of insulin in the association equilibrium with hexamers as the largest structures. After a lag period of about 8 days the solutions showed continuously increasing scattering intensities but did not evolve perceptible turbidity within the experimental period. A more rapid increase in scattering intensity was observed in diluted than in concentrated solutions. The analysis of scattering data unexpectedly revealed that insulin species did not grow continuously. After the lag period one additional relatively restricted size distribution with particles of a mean radius of about 100 nm was found, the amount of which increased continuously with time. The occurrence of these particles seems to be related to adsorption phenomena of insulin to the solid interface. We assume the 100 nm-class of aggregates to be a transient state in the physical destabilization process of insulin solutions.

Combination oral contraceptives and cancer risk

Substantial evidence exists to suggest that the use of oral contraceptives alters the risk for some types of cancer. Use of oral contraceptives for one year or more will reduce the risk of endometrial cancer and epithelial ovarian cancer by 50%, with the protective effect lasting for at least 10 years. The risk for developing cervical cancer in women who have used oral contraceptives appears to be slightly increased, although two independent studies actually found a protective effect associated with oral contraceptive use. The protective effect was probably related to the increased screening frequency found in oral contraceptive users and not related to a biologically protective effect. Therefore, women should be encouraged to undergo regular Pap tests. Data regarding breast cancer, in general, show no increased risk associated with oral contraceptive use. The latency associated with the development of breast cancer does not allow a definitive conclusion, and further study will be required. Oral contraceptives appear to increase the risk for developing benign hepatocellular adenoma, but not hepatocellular carcinoma.