Pauling-Corey 0-sheet

Early studies by Pauling, Corey and Branson (1951), involving x-ray structures of small peptides and experimentation with molecular models, resulted in the prediction of several geometric patterns in proteins. Of these the OL-helix and p-sheets were subsequently encountered as dominant architectural features in numerous proteins. In more recent times also reverse turns (hairpin turns, y-tums) were postulated (Venkatachalam 1968) and then recognized as frequent contributors to peptide and protein conformation. 

We have suggested (Pauling Corey 1951s, 1951ft) that the process of contraction of muscle may involve the conversion of a contractile protein from a pleated sheet of nearly completely extended polypeptide chains to a double row of a-helices. This proposal seems to us to be a reasonable one which is compatible with our present knowledge of the structural chemistry of polypeptide chains, and which accounts for the usually observed extent of contraction of muscle, about 55 %. There is, however, little direct evidence in support of it at the present time. 

In the formulation of positional parameters for all of the atoms within this pseudo unit cell, we have assumed that the basic structural component is the antiparallel-chain pleated sheet (Pauling Corey, 1953). The reasons for this choice have been discussed in eonneetion with Bombyx mori, they are founded principally on the eonfidence we place in our knowledge of the geometry of polypeptide chains and hydrogen bonds. In particular, the values for the a- and 6-axis identity distances— 9-44 and 6-95 A— are almost exactly those calculated for the antiparallel-chain pleated sheet—9-5 and 7-0 A (Pauling Corey, 1953). 

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... 

Pauling, L., Corey, R.B. Configurations of polypeptide chains wifh favored orienfafions around single bonds two new pleated sheets. Proc. Natl. Acad. Sd. USA 37 729-740, 1951. 

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,... 

Pauling, L., and Corey, R. B. (1951). The pleated sheet, a new layer configuration of polypeptide chains. Proc. Natl. Acad. Sci. USA 37, 251-256. 

The second structural element to be proposed by Pauling and Corey was the P-pleated sheet (Figure 4.7). These sheets are made up of P-strands, typically from 5 to 10 residues long, in an almost fully extended conformation, aligned alongside one another with hydrogen bonds formed between the C=0 bonds of one strand and the NH of the other, and vice versa. The P-sheets are pleated (i.e. they undulate) with the Ca atoms alternatively a little above, or a little below the plane of the P-sheet, which means that the side chains project alternatively above and below the plane. P-Strands can interact to form two types of pleated sheets. 

Pauling and Corey recognized a second stable conformation of polypeptide chains —the extended chain or /3-pleated sheet (Figure 25-13). In this conformation the chains are fully extended with trans amide configurations. In this arrangement the distance is maximized between adjacent amino-acid... 

Pauling L, Corey RB. Configurations of polypeptide chains with favored orientations around single bonds Two new pleated sheets, Proc Natl Acad Sci. 1951 37 729. 

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).

Pauling and Corey worked feverishly now, expanding their ideas beyond the two helixes to additional structures for silk that they called pleated sheets. They also explored more complex structures for the proteins in feathers,... 

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. 

Pauling and Corey discovered another periodic structural motif, which they named the p pleated sheet (P because it was the second structure that they elucidated, the a helix having been the first). The P pleated sheet (or, more simply, the P sheet) differs markedly from the rodlike a helix. A polypeptide chain, called a P strand, in a P sheet is almost fully extended rather than being tightly coiled as in the a helix. A range of extended structures are sterically allowed (Figure 3.35). 

The jS form of keratin requires still additional models. And, continuing the order of decreasing certainty, these models are again less well corroborated by experimental observations than are the a-helix or a-keratin structures. Pauling and Corey (1598) presented the pleated sheets to explain /3-keratins. These sheets are made up of extended peptide chains H bonded essentially side by side. Two are shown in Fig. 10-7. 

In another paper, Pauling and Corey (1592) modified the two sheets slightly to achieve linear H bonds and give 7.0 A (antiparallel sheet) and 6.5 A (parallel sheet) as the repeat distances along the chains. The other major spacings of /3-keratin are explained as the distance between chains (4.6 A) and the distance between sheets (10 A). 

FIGURE 10-7 Pleated sheet structures proposed for /8-keratin, (a) The parallel-chain pleated sheet, (b) The anti parallel-chain pleated sheet. [From Pauling and Corey, Proc. NatL Acad. Sci. U.S. 37, 729-40 (1951).]... 

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