PubMed Health⌕ Search

Biomedical subjects

G D Fasman

Publications and source records attributed to G D Fasman.

At least 19 recordsLinked to original sources
PubMed1995

A poly(ethylene glycol) water-soluble conjugate of porin: refolding to the native state.

Porin, from Rhodabacter capsulatus, was chemically modified with methoxypoly(ethylene glycol) (m-PEG; molecular mass = 5000 Da) succinimidyl carbonate to yield methoxypoly(ethylene glycol)-porin (m-PEG-SC-Porin), as previously reported for bacteriorhodopsin [Sirokman, G., & Fasman, G. D. (1993) Protein Sci. 3, 1101-1170]. The m-poly(ethylene glycol)-porin (m-PEG-SC-Porin 50) conjugate, containing one poly(ethylene glycol) chain, was water soluble. The secondary structure of the conjugate in water was mainly random coil. Circular dichroism spectroscopy showed it was predominantly in the beta-pleated sheet structure in 0.6% octyltetraoxyethylene and 0.3 M LiCl, as was porin. A proteoliposome, containing the isolated porin conjugate, was prepared to measure permeability of the sugar stachyose. The m-PEG-SC-Porin 50 proteoliposome of porin maintained the permeability for the sugar, as did the proteoliposome of porin. The swelling rate of the conjugate versus the sugar was lower than it was for porin. This indicated that a pore in the conjugate exists but perhaps with a slightly different pore size. The refolding of the conjugate was studied by stepwise addition of trifluoroethanol (TFE) to lower the dielectric constant, simulating the insertion of porin into the membrane. An alpha-helical structure that did not exist in the native porin was formed with the m-PEG-SC-Porin 50, upon the addition of TFE, and the helicity increased with increasing concentrations of TFE. The m-PEG-SC-Porin 50 could be stepwise refolded to the native conformation, predominantly in the beta-sheet conformation, by the addition of hexafluoro-2-propanol in the 5-10% concentration range.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Membrane Permeability↗
PubMed1995

Solubilization of beta-amyloid-(1-42)-peptide: reversing the beta-sheet conformation induced by aluminum with silicates.

Plaques are one of the two lesions found in the brain of patients with Alzheimer disease. Using a synthetic peptide corresponding to rat beta-amyloid-(1-42) (beta A4), circular dichroism (CD) analyses were performed to examine the effect of Na4SiO4 on the conformational state produced by Al3+. A previous study on fragments of neuronal proteins involved in tangle formation had shown a conformational transition from a beta-pleated sheet to a soluble random coil upon addition of Na4SiO4. In the present study, CD measurements showed that the beta-pleated sheet conformation of beta A4 induced by Al3+ was reversed to the random coil soluble form by the addition of Na4SiO4. The tight binding of SiO4(4-) with Al3+ provides the mechanism for this transition. These results provide insight into the role of aluminum in the Alzheimer diseased brain and suggests that investigation of the use of silicates as a therapeutic agent.

Aluminum↗
PubMed1995

Complexes of aluminium with peptide ligands: a Fourier transform IR spectroscopic study.

Aluminium has been recognized to be a neurotoxic agent and a risk factor in Alzheimer's disease and other neuronal dysfunctions. CD spectroscopic studies on two synthetic fragments of the human neurofilament protein midsized subunit (NF-M), and their alanine-for-serine-substituted and/or serine-phosphorylated derivatives showed the formation of stable, citric acid resistant complexes of Al3+ with peptide ligands [M. Hollósi, Z. M. Shen, A. Perczel, and G. D. Fasman (1994) Proc. Natl. Acad. Sci. USA, vol. 9, pp. 4902-4906]. In the case of Ser-phosphorylated fragments, a beta-sheet inducing effect of Ca2+ and Al3+ ions was observed. However, the serine-containing parent peptides, NF-M13 (KSPVPKSPVEEKG) and NF-M17 (EEKGKSPVPKSPVEEKG), failed to show CD spectral changes reflecting beta-sheet formation upon addition of Al3+ ions. On the basis of the amide I region of the Fourier transform ir spectra, in trifluoroethanol, the peptide backbone of NF-M17 and NF-M17 (A6A11) shows marked changes in the presence of Al3+. The most significant spectral differences are seen in the carboxyl region (> 1700 cm-1). The high-frequency component bands above 1760 cm-1 in both spectra belong to the C = O of undissociated CF3COOH. Another strong band at 1710 cm-1 which appears only in the spectrum of NF-M17 (A6A11)(NF-M17 with Ser6 and Ser11 replaced by Ala) can be assigned to the side chain or C-terminal COOH groups. The differential protonation state of the carboxyl groups in the two peptides suggests the formation of Al3+ complexes of different structure and stability.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗
PubMed1994

The solubilization of model Alzheimer tangles: reversing the beta-sheet conformation induced by aluminum with silicates.

Neurofibrillary tangles are one of two lesions found in the brain of Alzheimer disease victims. With synthetic peptide fragments of human neurofilament NF-M17 (Glu-Glu-Lys-Gly-Lys-Ser-Pro- Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly, phosphorylated and unphosphorylated), CD studies were done to examine the effect of sodium orthosilicate on the conformational state produced by Al3+ on fragments of neuronal proteins. Previous studies had shown a conformational transition from alpha-helix and random to beta-pleated sheet upon addition of Al3+ to both phosphorylated and unphosphorylated peptides. If sufficient quantities of Al3+ are added, the peptide precipitates from solution. The ability to reverse or slow the progression of aggregation was examined. Al3+ binding was reversed with 1-2 molar equivalents of sodium orthosilicate (with respect to Al3+), altering the conformation from beta-sheet to random coil and resulting in a CD spectrum similar to that of the initial peptide. The tight binding of the SiO4(4-) with the Al3+ provides the mechanism for this transition. These results provide additional information toward understanding the role of aluminum in the Alzheimer diseased brain and suggest the investigation of the possible use of silicates as a therapeutic agent.

Aluminum↗
PubMed1994

Study of Al3+ binding and conformational properties of the alanine-substituted C-terminal domain of the NF-M protein and its relevance to Alzheimer's disease.

NF-M13 [H-(Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH], NF-M17 [H-(Glu-Glu-Lys-Gly-Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly) -OH], and their phosphorylated derivatives, representing the C-terminal phosphorylation domain of the neurofilament protein midsize subunit, have four possible binding sites for metal ions: the COO- group of glutamate, the OH group of the serine residue, the PO3H- group of phosphoserine (when present), and the COO- at the terminus of the peptide chain. The CD titration of the phosphorylated neurofilament fragments with Al3+ and Ca2+ yielded a significant conformational change that resulted in conformations containing high beta-pleated-sheet contents, which precipitate on standing (intermolecular complex). Al3+ binding to the unphosphorylated NF-M13 and NF-M17 did not exhibit this behavior. Several alanine analogues of the parent NF-M17 peptide were synthesized in order to determine the relationship between metal ions and possible binding sites. CD titration of analogues with Ca2+ indicated that the critical residues of NF-M17 for Ca(2+)-induced conformational changes, from random to beta-pleated sheet, are the N-terminal serine or both phosphorylated serines. Al(3+)-induced conformational changes suggest that the critical sites of NF-M17 yielding the beta-pleated-sheet structure are the four glutamates or phosphorylated serines, especially the C-terminal SerP. On the basis of the titration data, it is very likely that analogues with a serine in position 11 form a stable intramolecular complex with Al3+ that, however, does not result in the adoption of the beta-conformation. Back-titration with citric acid fails to reverse the Al(3+)-induced conformational changes of the phosphorylated peptides. The above results, especially the possible formation of intramolecular and intermolecular Al3+ complexes, may have relevance to the molecular mechanism, through which the neurotoxin Al3+ gives rise to the formation of neurofilament tangles.

Alanine↗
PubMed1994

Stable intrachain and interchain complexes of neurofilament peptides: a putative link between Al3+ and Alzheimer disease.

The etiologic role of Al3+ in Alzheimer disease has been controversial. Circular dichroism (CD) spectroscopic studies on two synthetic fragments of human neurofilament protein mid-sized subunit (NF-M), NF-M13 (KSPVPKSPVEEKG) and NF-M17 (EEKGKSPVPKSPVEEKG), and their alanine-substituted and/or serine-phosphorylated derivatives were carried out in an attempt to find a molecular mechanism for the effect of Al3+ to induce aggregation of neuronal proteins or their catabolic fragments. Al3+ and Ca2+ ions were found to induce beta-pleated sheet formation in the phosphorylated fragments. The cation sensitivity depended on the length and charge distribution of the sequence and site of phosphorylation. Al3+-induced conformational changes were irreversible to citric acid chelation, whereas Ca(2+)-induced conformational changes were reversible with citric acid. Studies of the alanine derivatives demonstrated which residues affected Al3+ or Ca2+ binding. Peptides containing at least one free (nonphosphorylated) serine residue were shown to form an intramolecular Al3+ complex, rather than an intermolecular one. In the intramolecular (intrachain) complex, the ligand function of the deprotonated serine hydroxyl was delineated [(Al.pepH-1)-type complex]. Ca2+ ions did not show a tendency for intramolecular complexing. The potential role of Al3+ in Alzheimer disease tangle and plaque formation is strongly suggested.

Aluminum↗
PubMed1994

CD and Fourier transform ir spectroscopic studies of peptides. II. Detection of beta-turns in linear peptides.

Comparative CD and Fourier transform ir (FTIR) spectroscopic data on N-Boc protected linear peptides with or without the (Pro-Gly) beta-turn motif (e.g., Boc-Tyr-Pro-Gly-Phe-Leu-OH and Boc-Tyr-Gly-Pro-Phe-Leu-OH) are reported herein. The CD spectra, reflecting both backbone and aromatic contributions, were not found to be characteristic of the presence of beta-turns. In the amide I region of the FTIR spectra, analyzed by self-deconvolution and curve-fitting methods, the beta-turn band showed up between 1639 and 1633 cm-1 in trifluoroethanol (TFE) but only for models containing the (Pro-Gly) core. This band was also present in the spectra in chloroform but absent in dimethylsulfoxide. These findings, in agreement with recent ir data on cyclic models and 3(10)-helical polypeptides and proteins in D2O [see S. J. Prestrelski, D. M. Byler, and M. P. Thompson (1991), International Journal of Peptide and Protein Research, Vol. 37, pp. 508-512; H. H. Mantsch, A. Perczel, M. Hollósi, and G. D. Fasman (1992), FASEB Journal, Vol. 6, p. A341; H. H. Mantsch, A. Perczel, M. Hollósi, and G. Fasman (1992), Biopolymers, Vol. 33, pp. 201-207; S. M. Miick, G. V. Martinez, W. R. Fiori, A. P. Todd, and G. L. Millhauser (1992), Nature, Vol. 359, pp. 653-655], suggest that the amide I band, with a major contribution from the acceptor C = O of the 1<--4 intramolecular H bond of beta-turns, appears near or below 1640 cm-1, rather than above 1660 cm-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

FT-IR spectroscopy indicates that Ca(2+)-binding to phosphorylated C-terminal fragments of the midsized neurofilament protein subunit results in beta-sheet formation and beta-aggregation.

The Fourier-transform infrared (FT-IR) spectra in trifluoroethanol (TFE) of phosphorylated peptides, NF-M17(Ser6P) and NF-M17(Ser11P) representing the C-terminal repeating domain of the midsized neurofilament protein subunit (NF-M) have been measured. In the absence of Ca2+ ions both phosphopeptides adopt predominantly aperiodic conformation with minor amounts of beta-turns, 3(10) helix or beta-pleated sheet. Addition of Ca(ClO4)2 results in opaque solutions, and in the case of the Ser6P peptide, precipitation. The infrared spectra of the supernatants reflect the presence of unordered and beta-sheet structure. The infrared spectrum of the solid Ca(2+)-complex of NF-M17 (Ser6P) in a KBr pellet shows amide component bands at 1654 (alpha-helix or loops) and 1626.5 cm-1 (beta-sheet). The high intensity of the beta-sheet component suggests extensive beta-aggregation. The data reported herein give an infrared spectroscopic support to our previous findings that upon Ca2+ binding, phosphorylated NF-M fragments undergo a marked conformational change which gives rise to partial beta-sheet formation and beta-aggregation. This observation may have relevance to the molecular events which lead to the accumulation of abnormal proteineous structures in Alzheimer's disease.

Amino Acid Sequence↗
PubMed1993

Conformational change of chaperone Hsc70 upon binding to a decapeptide: a circular dichroism study.

The conformation of bovine Hsc70, a 70-kDa heat shock cognate protein, and its conformational change upon binding to decapeptides, was studied by CD spectroscopy and secondary structure prediction (Chou, P.Y. & Fasman, G.D., 1974, Biochemistry 13, 222-245). The CD spectra were analyzed by the LINCOMB method, as well as by the convex constraint analysis (CCA) method (Perczel, A., Park, K., & Fasman, G.D., 1992, Anal. Biochem. 203, 83-93). The result of the CD analysis of Hsc70 (15% alpha-helix, 24% beta-sheet, 24% beta-turn, and 38% remainder) was very similar to the predicted secondary structure for the beta-sheet (24%) and the beta-turn (29%). However, there is disagreement between the alpha-helical content by CD analysis (15%) and the predicted structure (30%). In spite of the fact that the decapeptides contained a considerable amount of beta-sheet (22%), the interaction of the heat shock protein with the peptide resulted in an overall decrease in the content of beta-sheet conformation (-15%) of the complex. This may be due to induction of a molten globule state. The result of the CCA analysis indicated that the Hsc70 undergoes a conformational change upon binding the decapeptides.

Amino Acid Sequence↗
PubMed1993

Distinguishing transmembrane helices from peripheral helices by circular dichrosim.

The interpretation of the circular dichroism (c.d.) spectra of proteins to date requires additional secondary structural information of the proteins to be analysed (e.g., X-ray or n.m.r. data). Therefore these methods are inappropriate for a c.d. database whose secondary structures are unknown, as in the case of the membrane proteins. The Convex Constraint Analysis algorithm [Perczel, Hollósi, Tusnady, and Fasman (1991) Convex constraint analysis: a natural deconvolution of circular dichroism curves of proteins. Protein Eng. 4, 669-679] operates on a collection of c.d. spectral data to extract the common spectral components with their spectral weights. The linear combinations of these derived 'pure' c.d. curves can reconstruct the original data set with great accuracy. For a membrane protein data set, the five-component spectra so obtained from the deconvolution consisted of two different types of alpha-helices (the alpha-helix in the soluble domain and the alpha1-helix, for the transmembrane alpha-helix), a beta-pleated sheet, a class-C-like spectrum related to beta-turns and a spectrum correlated with the unordered conformation. The deconvoluted c.d. spectrum for the alpha1-helix was characterized by a positive red-shifted band in the range 195-200 nm (+95,000 degrees.cm2-dmol-1), with the intensity of the negative band at 208 nm being slightly less negative than that of the 222 nm band (-50,000 and -60,000 degrees.cm2.dmol-1 respectively) in comparison with the regular alpha-helix, with a positive band at 190 nm and two negative bands at 208 and 222 nm with magnitudes of +70,000, -30,000 and -30,000 degrees.cm2.dmol-1 respectively.

Animals↗
PubMed1992

How reverse turns may mediate the formation of helical segments in proteins: an x-ray model.

The three-dimensional structure of a protein is the assembly of different secondary structural elements, such as alpha-helices, beta-pleated sheets, and beta-turns. Although the conformation of hundreds of proteins has been elaborated in the solid state, only a vague understanding of the mechanism of their conformational folding is known. One facet of this topic is the conformational interconversion of one or more beta-turns to a helical structure (and vice versa), which may also be related to the formation of helix-turn-helix motifs often observed in globular proteins. Based on a comprehensive structural analysis of proteins, Sundaralingam and Sekharudu [Sundaralingam, M. & Sekharudu, Y. C. (1989) Science 244, 1333-1337] previously suggested that "structure-water" molecules in proteins may mediate such a conformational change. An x-ray crystal structure determination of t-butoxycarbonyl (Boc)-Val-Ser-NHCH3 reveals (i) an ideal type I beta-turn backbone conformation and (ii) a hydrogen-bond network more typical of an alpha-helix than a beta-turn conformation. The molecular packing of this simple beta-turn model reported here provides a plausible and simple alternative of how a beta-turn-like conformation may serve as a conformational template for helical-structure formation (and vice versa) during the folding procedure.

Hydrogen Bonding↗
PubMed1992

Conformational and functional properties of peptides covering the intersubunit region of influenza virus hemagglutinin.

The functionally active part of influenza virus hemagglutinin was investigated through the synthesis of a series of peptides representing different parts of the intersubunit region. Secondary structure prediction, circular dichroism and Fourier transform infrared spectroscopic studies were undertaken to investigate the secondary structure of these peptides. The peptide fragments were found to adopt multiple conformations, depending on their concentration in solution, the presence of the non-ionic detergent octyl-beta-D-glucoside and the polarity of the solvent. The results of biological studies with these peptide fragments are discussed in relation to their conformation, as inferred from the spectroscopic analysis.

Amino Acid Sequence↗
PubMed1992

Analysis of the circular dichroism spectrum of proteins using the convex constraint algorithm: a practical guide.

Due to the time scale of circular dichroism (CD) measurements, it is theoretically possible to deconvolute such a spectrum if the pure CD spectra differ significantly from one another. In the last decade several methods have been published aiming at obtaining the conformational weights, or percentages (which are the coefficients for a linear combination) of the so-called typical secondary structural elements making up the three-dimensional structure of proteins. Two methods that can be used to determine the secondary structures of proteins are described here. The first method, called LINCOMB, is a simple algorithm based on a least-squares fit with a set of reference spectra representing the known secondary structures and yielding an estimation of weights attributed to alpha-helix, beta-pleated sheet (mainly antiparallel), beta-turns, unordered form, and aromatic/disulfide (or nonpeptide) contributions of the protein being analyzed. This method requires a "template" or reference curve set, which was obtained from the second method. The second method, "convex constraint analysis," is a general deconvolution method for a CD spectra set of any variety of conformational type. The algorithm, based on a set of three constraints, is able to deconvolute a set of CD curves to its common "pure"-component curves and conformational weights. To analyze a single CD spectrum with this method, the spectrum is appended to the data set used as a reference data set. As a way to determine the reliability of the algorithm and provide a guideline to its usage, some applications are presented.

Algorithms↗
PubMed1992

Metal ion-induced conformational changes of phosphorylated fragments of human neurofilament (NF-M) protein.

The NF-M subunit of human neurofilaments has a C-terminal repeating 13-mer sequence. The 13-mer (Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly) (NF-M13) and 17-mer (Glu-Glu-Lys-Gly)-(NF-M13) sequences were synthesized, as were both the mono- and diphosphorylated Ser species. Circular dichroism (c.d.) studies and c.d. titrations with Al3+ and Ca2+ were performed. The conformation of the phosphorylated and unphosphorylated material was random in water. Deconvolution of the c.d. spectra, in trifluoroethanol, of the untitrated samples yielded a high content of unordered structure, similar to the poly-L-proline II structure. Titration of the phosphorylated species with Al3+ or Ca2+ caused a surprising conformational change to occur, yielding a high content of beta-pleated sheet structure. A mechanism of metal binding to the phosphofragments is proposed which may be relevant to the formation of neurofibrillary tangles in Alzheimer's disease.

Aluminum↗
PubMed1992

Quantitative analysis of cyclic beta-turn models.

The beta-turn is a frequently found structural unit in the conformation of globular proteins. Although the circular dichroism (CD) spectra of the alpha-helix and beta-pleated sheet are well defined, there remains some ambiguity concerning the pure component CD spectra of the different types of beta-turns. Recently, it has been reported (Hollósi, M., Kövér, K.E., Holly, S., Radics, L., & Fasman, G.D., 1987, Biopolymers 26, 1527-1572; Perczel, A., Hollósi, M., Foxman, B.M., & Fasman, G.D., 1991a, J. Am. Chem. Soc. 113, 9772-9784) that some pseudohexapeptides (e.g., the cyclo[(delta)Ava-Gly-Pro-Aaa-Gly] where Aaa = Ser, Ser(OtBu), or Gly) in many solvents adopt a conformational mixture of type I and the type II beta-turns, although the X-ray-determined conformation was an ideal type I beta-turn. In addition to these pseudohexapeptides, conformational analysis was also carried out on three pseudotetrapeptides and three pseudooctapeptides. The target of the conformation analysis reported herein was to determine whether the ring stress of the above beta-turn models has an influence on their conformational properties. Quantitative nuclear Overhauser effect (NOE) measurements yielded interproton distances. The conformational average distances so obtained were interpreted utilizing molecular dynamics (MD) simulations to yield the conformational percentages. These conformational ratios were correlated with the conformational weights obtained by quantitative CD analysis of the same compounds. The pure component CD curves of type I and type II beta-turns were also obtained, using a recently developed algorithm (Perczel, A., Tusnády, G., Hollósi, M., & Fasman, G.D., 1991b, Protein Eng. 4(6), 669-679). For the first time the results of a CD deconvolution, based on the CD spectra of 14 beta-turn models, were assigned by quantitative NOE results. The NOE experiments confirmed the ratios of the component curves found for the two major beta-turns by CD analysis. These results can now be used to enhance the conformational determination of globular proteins on the basis of their CD spectra.

Amino Acid Sequence↗
PubMed1992

Differentiation between transmembrane helices and peripheral helices by the deconvolution of circular dichroism spectra of membrane proteins.

The interpretation of the circular dichroism (CD) spectra of proteins to date requires additional secondary structural information of the proteins to be analyzed, such as X-ray or NMR data. Therefore, these methods are inappropriate for a CD database whose secondary structures are unknown, as in the case of the membrane proteins. The convex constraint analysis algorithm (Perczel, A., Hollósi, M., Tusnády, G., & Fasman, G. D., 1991, Protein Eng. 4, 669-679), on the other hand, operates only on a collection of spectral data to extract the common spectral components with their spectral weights. The linear combinations of these derived "pure" CD curves can reconstruct the original data set with great accuracy. For a membrane protein data set, the five-component spectra so obtained from the deconvolution consisted of two different types of alpha helices (the alpha helix in the soluble domain and the alpha T helix, for the transmembrane alpha helix), a beta-pleated sheet, a class C-like spectrum related to beta turns, and a spectrum correlated with the unordered conformation. The deconvoluted CD spectrum for the alpha T helix was characterized by a positive red-shifted band in the range 195-200 nm (+95,000 deg cm2 dmol-1), with the intensity of the negative band at 208 nm being slightly less negative than that of the 222-nm band (-50,000 and -60,000 deg cm2 dmol-1, respectively) in comparison with the regular alpha helix, with a positive band at 190 nm and two negative bands at 208 and 222 nm with magnitudes of +70,000, -30,000, and -30,000 deg cm2 dmol-1, respectively.

Adenosine Triphosphatases↗
PubMed1992

Deconvolution of the circular dichroism spectra of proteins: the circular dichroism spectra of the antiparallel beta-sheet in proteins.

A recently developed algorithm, called Convex Constraint Analysis (CCA), was successfully applied to determine the circular dichroism (CD) spectra of the pure beta-pleated sheet in globular proteins. On the basis of X-ray diffraction determined secondary structures, the original data set used (Perczel, A., Hollosi, M., Tusnady, G. Fasman, G.D. Convex constraint analysis: A natural deconvolution of circular dichroism curves of proteins, Prot. Eng., 4:669-679, 1991), was improved by the addition of proteins with high beta-pleated sheet content. The analysis yielded CD curves of the pure components of the main secondary structural elements (alpha-helix, antiparallel beta-pleated sheet, beta-turns, and unordered conformation), as well as a curve attributed to the "aromatic contribution" in the wavelength range of 195-240 nm. Upon deconvolution the curves obtained were assigned to various secondary structures. The calculated weights (percentages determining the contributions of each pure component curve in the measured CD spectra of a given protein) were correlated with the X-ray diffraction determined percentages in an assignment procedure and were evaluated. The Pearson product correlation coefficients (R) are significant for all five components. The new pure component curves, which were obtained through deconvolution of the protein CD spectra alone, are promising candidates for determining the percentages of the secondary structural components in globular proteins without the necessity of adopting an X-ray database. The CD spectrum of the CheY protein was interesting because it has the characteristic shape associated with the alpha-helical structure, but upon analysis yielded a considerable amount of beta-sheet in agreement with the X-ray structure.

Circular Dichroism↗