Corey, a-helix

In detail The first lobe (residues 1 -39 and 85-129) contains four helices that are close to the Pauling—Corey a-helix type, and one singleturn 310-type helix. There are short stretches (each five to nine residues) of backbone loops and turns connecting the helices. Three a helices (helix A, residues 4—15 helix C, residues 88—99 helix D, residues 108-115) are on the protein surface and are partially exposed to solvent. The a helix (B) consisting of residues 24-36 is totally buried. The 310 helix (residues 119—124) is partially exposed to solvent. The second lobe (residues 40-84) contains a three-stranded antiparallel y3-pleated... 

The primary structure of a peptide is its ammo acid sequence We also speak of the secondary structure of a peptide that is the conformational relationship of nearest neighbor ammo acids with respect to each other On the basis of X ray crystallographic studies and careful examination of molecular models Linus Pauling and Robert B Corey of the California Institute of Technology showed that certain peptide conformations were more stable than others Two arrangements the a helix and the (5 sheet, stand out as... 

Figure 1.10 Helical conformations in polymer molecules, (a) A vinyl polymer with R substituents has three repeat units per turn, (b) The a helix of the protein molecule is stabilized by hydrogen bonding. [From R. B. Corey and L. Pauling,/ end. Inst. Lombardo Sci. 89 10 (1955).]...

Proteins are complex molecules, typically containing several thousand atoms. Although Pauling and Corey proposed the a helix and the 3 sheet as the main secondary structural elements of proteins in 1951, and the crystal structure of myoglobin was reported by John Kendrew in 1958,... 

The term secondary structure refers to the local conformation of some part of a polypeptide. The discussion of secondary structure most usefully focuses on common regular folding patterns of the polypeptide backbone. A few types of secondary structure are particularly stable and occur widely in proteins. The most prominent are the a helix and /3 conformations described below. Using fundamental chemical principles and a few experimental observations, Pauling and Corey predicted the existence of these secondary structures in 1951, several years before the first complete protein structure was elucidated. 

Protein Architecture—a Helix Pauling and Corey Were aware of the importance of hydrogen bonds in orient-... 

An especially favorable conformation of a polypeptide chain that was originally deduced by Pauling and Corey is the alpha helix (Figure 25-11). The principal feature of the a helix is the coiling of the polypeptide chain in... 

Fig. 7. The a-helix which occurs in some regions of the polypeptide chains of many proteins. (The atoms of the chain are picked out by shading R signifies the side-chain characteristic of each individual amino acid.) [From a photograph kindly provided by the late Professor R. B. Corey.]...

Pauling and Corey proposed the a-helix structure for a-keratins. 

Alternate Helical Structures. Since Pauling and Corey s description of the a helix [76], many other helical structures for polypeptides have been proposed and described. However, most of them are rare or found only in homopolymeric systems. These include the helix, the it helix, and the an helix. 

Figure II-2 Major elements of secondary structure of proteins. Left, the a-helix right, representation of the antiparallel pleated sheet structures for polypeptides. (After Pauling, L., and R. B. Corey (1951). Proc Natl Acad Sci USA 37 729).

The Pauling-Corey alpha helix. In addition to the right-handed helix shown, a left-handed one is also possible (with the same t-amino acids). In proteins, the helix always seems to be right-handed. [Reprinted by permission from L. Pauling, The Nature of the Chemical Bond, p. 500, Cornell Univ. Press, Ithaca, NY I960).]... 

The diffraction patterns displayed by helical synthetic polypeptides are similar to those first discovered by Astbury for fibrous proteins (Astbury and Street, 1931 Astbury and Woods, 1933), with the exception that a meridional spacing here occurs at 5.1 A instead of 5.4 A. This particular pattern, which Astbury designated the a-pattern, may be reconciled with the a-helix if the helices are themselves coiled to form a cablelike structure, as suggested independently by Crick (1952, 1953) and by Pauling and Corey (1953). 

The observation by Mac Arthur (1943) and Perutz (1951) of a meridional reflection in a-keratin of spacing 1.5 A equal to the axial translation per residue in the a-helix provided considerable support for this model but, as noted by Pauling and Corey, the strong meridional arc of spacing 5.15 A was not accounted for without further assumptions. 

Can a polypeptide chain fold into a regularly repeating structure In 1951, Linus Pauling and Robert Corey proposed two periodic structures called the a helix (alpha helix) and the p pleated sheet (beta pleated sheet). Subsequently, other structures such as the P turn and omega ( Q) loop were identified. Although not periodic, these common turn or loop structures are well defined and contribute with a helices and P sheets to form the final protein structure. 

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