Helical conformation circular dichroism spectroscopy

Blackwell and his co-workers have used circular dichroism spectroscopy to study the interactions of glycosaminoglycans with collagen, and with synthetic cationic polypeptides. In the absence of glycosaminoglycans, poly-L-lysine and poly-L-arginine exist in an extended charged coil conformation. Glycosaminoglycans bind to these cationic polypeptides and cause them to assume an a-helical conformation. In a series of systematic studies (76-83). Blackwell and his co-workers... 

There has been considerable recent interest in chiral CEPs in which polymer chains (or aggregates of polymer chains) adopt a one-handed helical arrangement. Circular dichroism (CD) spectroscopy provides a powerful tool to probe the chain conformation (and preferred hand) in such chiral polymers. This spectroscopic technique measures the difference in absorption of left- and right-hand circularly polarized light by a chiral sample as follows ... 

The conformational changes which have been described so far are probably all relatively small local changes in the structure of H,K-ATPase. This has been confirmed by Mitchell et al. [101] who demonstrated by Fourier transform infrared spectroscopy that a gross change in the protein secondary structure does not occur upon a conformational change from Ei to 3. Circular dichroism measurements, however [102,103], indicated an increase in a-helical structure upon addition of ATP to H,K-ATPase in the presence of Mg and... 

The next three sections (Sections 7.7.1, 7.7.2, and 7.7.3) cover fluorescence spectroscopy, I15-18 infrared, and circular dichroism, three powerful approaches to characterize the structure and conformational considerations of synthetic peptides. Section 7.7.1 deals with the use of fluorophores and broad aspects of fluorescence spectroscopy to characterize conformational aspects of peptide structure. In a similar manner, Section 7.7.2 covers a broad aspect of the uses of infrared (IR) techniques to study peptide conformations 19-22 Many IR techniques are discussed, as are approaches for the study of specific peptidic structures including amyloid, p-turn, and membrane peptides. Finally, there is a section on circular dichroism (Section 7.7.3) that covers the major issues of concern for peptide synthetic chemists such as the assignments of a-helix, 310-helix, -sheets and P-turns, and polyproline helices 23-25 There is also a brief description of cyclic peptides. 

Experimental results have shown that the hydrodynamic conformation of AFGP corresponds to an extended structure (Ahmed et al., 1975). Raman spectroscopy on this system (Tomimatsu et al., 1976) revealed that the solution spectra in the amide I region is dominated by extended conformations, consistent with the earlier results (DeVries et al., 1970), where circular dichroism also showed no extensive regions of helices. Such an open structure in turn leads to open exposure of the disaccharide groups. 

In the case of m=2 in dimethylsulfoxide solution, the right-handed a-helical main chain conformation has been confirmed by the circular dichroism in the vibrational region (VCD). (A preliminary result of joint research with Professor T, Keiderling, University of Illinois at Chicago). By the VCD spectroscopy one can obtain information on the main chain conformation of polypeptides without any interference by the side-chain chromophores ( ). The VCD couplet... 

Information about the secondary structures (a-helices, /5-sheets, random coil) can be useful for understanding conformation changes of proteins upon the immobilization process. More specifically, circular dichroism (CD) [70] and FT-IR spectroscopy [56, 58, 61, 71-73] have been applied to study the structural characteristics of various proteins adsorbed on mineral surfaces. Kondo and coworkers [70] have studied the modification in a-helix content of proteins adsorbed on ultrafine silica particles with CD and found a decrease upon immobilization. Circular dichroism is not usually used because this technique is applicable only for the study of enzymes immobilized on nano-sized mineral particles due to problems arising from light scattering effects. On the other hand, infrared spectroscopy does not suffer from light scattering perturbations and has thus been used for the study of the conformation of proteins when they are immobilized on solid supports [57, 58]. 

Extensive NMR and circular dichroism [131, 132] spectroscopy was used to examine the structure and stability of HBS a-helices the conformation of these compounds is also supported by an X-ray crystal structure that is presented in Fig. 19 [133]. These studies demonstrate that the HBS approach affords stable, short a-helices from biologically relevant sequences. 

Pioneering work by the Alix laboratory on the secondary structure of human elastin and the solubilized K-elastin, estimated the molecule to be composed of 10% a-helices, 35% P-strands and 55% undefined conformation. These estimations were based on Fourier transform infrared (FTIR), near infrared Fourier transform Raman spectroscopy and circular dichroism (CD) (15). To further investigate the nature of the elasticity, polypeptides of hydrophobic sequences containing exons 3, 7, and 30 of human elastin were analyzed by CD and Classic Raman spectroscopy, revealing polyproline II (PPII) helix secondary structures in both the aqueous and solid phase. Further analysis of exon 30 by FTIR spectroscopy determined that this sequence was characterized by both PPII as well as p-sheets structures (15). The presence of these structures were dependent on temperature, concentration and / or time, where lower temperatures and concentrations favored the PPII structure and higher temperatures and concentrations favored p-sheets (16). 

Fluorescence spectroscopy in combination with circular dichroism (CD), optical rotatory dispersion. X-ray crystallography, UV and NMR spectroscopy of the main chain is a powerful probe for identifying helical conformation, uniformity, and rigidity in polymers. In recent years, these techniques have been applied extensively to investigate the structures of polysilanes in both the solid state and in solution and it is now clear that after electronic structure main chain helicity is the principal determinant of the properties of polysilanes. In... 

Circular dichroism (CD) spectroscopy is based on the difference of absorption of right and left circularly polarized radiation by chiral (dissymmetric) molecules. In peptide research CD spectra can give valuable information on the conformation of peptide molecules in solution. The differences in absorption (ellipticities, 9) are pronounced in the 200 to 220 nm region. The positive or negative Cotton effects allow empirical statements on the arrangement of peptide chains, through comparisons with the CD spectra of peptides that have helical, pleated sheet or random coil conformations, established by other means, e.g. by X-ray diffraction studies. Optical rotatory dispersion (ORD) spectroscopy, which is based on the different refraction of circularly polarized light by chiral compounds, is the older... 

Differential scanning calorimetry (DSC), circular dichroism and NMR spectroscopy are convenient methods to demonstrate the existence of a helical conformation (or at least the existence of an ordered conformation in a given situation) and to determine the thermodynamic conditions for the helix-coil transition [11, 12]. 

Despite the sequence identity of PrP and PrP from the same species, they display quite different physical properties. Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy reveal that PrP - is essentially a-helical and devoid of P-pleated sheet structure, whereas the P-pleated sheet content of PrP is -40%, while PrP27-30 contains more than 50 % p-pleated sheet. Procedures that destroy the infectivity of PrP27-30 and PrP (e. g. purification by SDS-polyacrylamide gel electrophoresis or treatment with alkali) also substantially reduce the P-pleated sheet content. It therefore appears that the difference between the normal and disease-causing isoforms of PrP is entirely conformational and related to the respective contents of a-helical structure and P-pleated sheet structure. 

In the line of these studies, we investigated rod-like PEC particles using stiff cationic a-helical PEL as the templating PEL component to be complexed by a flexible polyanion [16]. On the one hand, the a-helix of PLL might be induced by media parameters like pH or certain salt ions, as used for the fabrication of anisotropic related PEM. On the other hand, early work by Shinoda et al. [89] based on circular dichroism (CD) spectroscopy reported induction of the a-helical conformation of PLL by certain polyanions. PAC was used, which was claimed to form a stoichiometric left-handed superhelix around the right-handed a-helix of PLL. However, this polyanion/PLL templating effect on the intermacromolecular order was not studied further on the supramolecular, nanoscopic, or even colloid level. 

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