Polypeptide helical

Tang HY, Zhang DH (2010) General route toward side-chain-fimctionalized alpha-helical polypeptides. Biomacromolecules 11 1585-1592... 

Torii, H., and M. Tasumi. 1993. Infrared Intensities of Vibrational Modes of an a-helical Polypeptide Calculations Based on the Equilibrium Charge/Charge Flux (ECCF) Model. J. Mol. Struct. 300,171-179. 

Helical complexes, chirality in, 26 803-804 Helical polypeptide, 24 58 Helical ribbon impeller, 16 690, 691 Helicobacter pylori, 15 303 antibiotic resistant, 3 36 Helio-photocatalysis, 19 78, 95 Heliotridine, 2 80... 

The long side chains of a homopolypeptide have remarkable motional freedom about multiple bonds, while the main chain forms the secondary regular conformation such as a-helix, /1-sheet, and turn, which are rigid structures. The macroscopic properties of the rigid a-helical polypeptide, therefore, highly depends on the dynamic structure of the side chains so that a lot of studies on the side chain dynamics of the a-helical polypeptides have been carried out in the solid and solution states.12,14,29 66... 

While many studies of helical polypeptides and proteins were reported and the understanding of how to engineer four-helix bundle proteins increased the... 

The a-helix CD spectrum is remarkably insensitive to solvent. One apparent exception is poly(Ala) in HFIP.1471 The CD amplitude for poly(Ala) in HFIP is only about half that of typical a-helical polypeptides, the CD bands are shifted several nm to the blue, and the long-wavelength njr band is observed as a shoulder rather than a discrete band. These features are unique to poly(Ala), as other helix-forming polypeptides exhibit normal CD spectra in... 

Since Robinson [1] discovered cholesteric liquid-crystal phases in concentrated a-helical polypeptide solutions, lyotropic liquid crystallinity has been reported for such polymers as aromatic polyamides, heterocyclic polymers, DNA, cellulose and its derivatives, and some helical polysaccharides. These polymers have a structural feature in common, which is elongated (or asymmetric) shape or chain stiffness characterized by a relatively large persistence length. The minimum persistence length required for lyotropic liquid crystallinity is several nanometers1. 

On the other hand, the deposition process is also important to prepare blend samples. A mixture of homopolypeptide solutions in which they take a random coiled structure are added into a poor solvent. For polypeptides, water is a poor solvent in general. If the hydration rate is different for each polypeptides, they form their preferred secondary structures by themselves and then do not blend with each other. On the basis of this assumption, in order to make the hydration at the same time, the solution is added to alkaline water. In this review, two kinds of quieting solvents such as water and alkaline water have been used. (Methods 1-4 and Method 5). Method 1 Helical polypeptide and (3-sheet polypeptide are dissolved in DCA and agitated... 

Nagai (5) also derived analytic expressions for the averages of such quantities as the number of helical sequences, the distribution of lengths (number of residues) of helical and randomly coiled sequences, and so forth. A set of these averages quantitatively defines the conformation of an interrupted helical polypeptide. It is important to recognize that these are all expressed in terms of the three fundamental parameters, N, s, and a. 

According to Nagai (5), the particle-scattering function P(0) of an interrupted helical polypeptide dissolved in a single-component solvent may be written... 

If 8 = 0, Eq. (C-35) gives app = , as should be expected. In the limit of infinitely large N, this equality is also recovered, regardless of the magnitude of S. Sample computations with a0 = 12 A, = 1.5 A, c= 10 4, and N = 1000 showed that app agreed with to within 1% if <5 = 0.2 and the difference remained about 2% even for S = 0.4. Therefore, it appears that, except in very special circumstances, the copolymer nature of interrupted helical polypeptides may scarcely affect the measurement of chain dimensions by light scattering. 

The curve drawn in Fig. 19 looks somewhat more like the theoretical curves in Fig. 11, but still exhibits no detectable minimum. It can be observed that the curve shows a strikingly steep rise in the region of high helical fractions, but the highest point reached is still far below the value which would be obtained if the sample assumed intact and rigid a-helical conformation. This fact indicates what great difficulty we encounter in experimental investigations of the dimensions of polypeptides in the vicinity of perfect helix. Furthermore, it indicates how sensitively the presence of even a small fraction of random-coil portions affects the overall shape of helical polypeptide molecules. 

In conclusion, the molecular dimensions of interrupted helical polypeptides can be described with fair accuracy by the theory based on Nagai s simplified model if a0 and at, especially the former, are treated as adjustable parameters. However, it is apparent that more experimental work ought to be attempted to determine the scope and limitations of this conclusion. 

It can be shown that the < 2> of an interrupted helical polypeptide is expressed by Eq. (C-3) for mean-square dipole moment of a random-coil unit. Precisely, this replacement is permissible if we neglect excluded-volume effects. Nagai (107) has shown theoretically that these effects on < 2> are virtually absent in randomly coiled macromolecules, even when they are appreciable on the molecular dimensions. It is our belief that Nagai s conclusion may apply to interrupted helical polypeptides as well. 

Since the mathematical expression for < u2) is equivalent to that for , measurements of should provide information which can be utilized to check the theory of , e.g. Eq. (C-3), for polypeptides in the helix-coil transition region. This idea, however, cannot be developed in straightforward fashion because there is no available theory to estimate of interrupted helical polypeptides from dielectric dispersion curves. Therefore, we are forced to proceed on some yet unproven assumptions, or even drastic approximations. 

N 019 "Conformational Energy Estimates for Helical Polypeptide Molecules"... 

Mean-Square Hydrophobic Moment (or Partially Helical Polypeptides" Hamed, M. M. Mattice, W. L. Biopolymers 1984, 23, 201. 

An individual polypeptide in the a-keratin coiled coil has a relatively simple tertiary structure, dominated by an a-helical secondary structure with its helical axis twisted in a left-handed superhelix. The intertwining of the two a-helical polypeptides is an example of quaternary structure. Coiled coils of this type are common structural elements in filamentous proteins and in the muscle protein myosin (see Fig. 5-29). The quaternary structure of a-keratin can be quite complex. Many coiled coils can be assembled into large supramolecular complexes, such as the arrangement of a-keratin to form the intermediate filament of hair (Fig. 4-1 lb). 

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