Parallel sheet structure

It is a supposition that the )9-sheet structure of neurotoxin is an essential structural element for binding to the receptor. The presence of -sheet structure was found by Raman spectroscopic analysis of a sea snake neurotoxin (2). The amide I band and III band for Enhydrina schistosa toxin were at 1672 cm and 1242 cm" respectively. These wave numbers are characteristic for anti-parallel -sheet structure. The presence of -sheet structure found by Raman spectroscopic study was later confirmed by X-ray diffraction study on Laticauda semifasciata toxin b. 

When s-MDH is viewed down the dyad, as shown in Fig. 1, the first half of the polypeptide chain (ySA to ySF) is folded into a reasonably defined region. The second half of the molecule ( 2F to H) comprises the remaining part of the molecule. It should be emphasized that the distribution of atoms is continuous there is no visible bilobal structure as has been seen in other enzymes (65). The first six segments of the extended chain (pA to pF) form a twisted region of parallel sheet structure. The schematic drawing in Fig. 1 does not show this twist. The amino terminal part of the sheet (/3A, pB, and / C) is on the surface of the... 

Parallel /3-sheets tend to be more regular than antiparallel /3-sheets. The range of (f) and i/t angles for the peptide bonds in parallel sheets is much smaller than that for antiparallel sheets. Parallel sheets are typically large structures those composed of less than five strands are rare. Antiparallel sheets, however, may consist of as few as two strands. Parallel sheets characteristically distribute... 

Another important parallel /3-array is the eight-stranded parallel j8-barrel, exemplified in the structures of triose phosphate isomerase and pyruvate kinase (Figure 6.30). Each /3-strand in the barrel is flanked by an antiparallel a-helix. The a-helices thus form a larger cylinder of parallel helices concentric with the /3-barrel. Both cylinders thus formed have a right-handed twist. Another parallel /3-structure consists of an internal twisted wall of parallel or mixed /3-sheet protected on both sides by helices or other substructures. This structure is called the doubly wound parallel j8-sbeet because the structure can be... 

FIGURE 6.41 The quaternary structure of liver alcohol dehydrogenase. Within each subunit is a six-stranded parallel sheet. Between the two subunits is a two-stranded antiparallel sheet. The point in the center is a C9 symmetry axis. (Jane Richardson)... 

Fig. 2.28 X-ray crystal structures of parallel sheet-forming and all-un//fce-/F -peptides 116 and 117 [10, 191]. Views along the parallel amide planes and crystal packing diagram show the parallel pleated sheet arrangement (view perpendicular to the amide planes).

Fig. 2.38 sheet forming y-peptides. (A) Crystal structure of the two stranded antiparallel sheet formed by a,j -unsaturated y-dipeptide 152 with a-methyl substituted residues [208], Both intermolecular H-bonds are characterized by a N---0 distance of 2.84 A and an angle (N-H- -O) ofl54.2°. (B) Crystal structure of the infinite parallel sheet arrangement formed by vinylogous dipeptide 153 [208], Intermolecular H-bonds are characterized by a N -O distance of 2.88 A and 3.24 A and an... 

Fig. 30 Model for the self-assembly of structure 2 into a double helix comprised of two ribbons, each of which consists of two parallel sheets. Reproduced with permission from Jahnke et al. [70].

Fig. 2 (a) Antiparallel and (b) parallel P-sheet structures of two peptide chains connected by hydrogen bonds... 

The p-pleated sheet structure occurs in fibrous as well as globular proteins and is formed by intermolecular hydrogen bonds between a carboxyl group oxygen of one amino acid and an amine hydrogen of an adjacent polypeptide chain. Parallel p-pleated sheets form when the adjacent polypeptide chains are oriented in one direction (from N-terminal to C-terminal end or vice versa). Antiparallel p-pleated... 

The /(-helix is a well-authenticated fold, having been observed in more than 20 crystal structures, mostly of secreted bacterial proteins (Jenkins and Pickersgill, 2001 Yoder and Jurnak, 1995 see also Kajava and Steven, this volume). In a /(-helix, the polypeptide chain winds around the molecular axis, each coil consisting of three short /(-strands with connecting turns (Fig. 11). Corresponding strands in successive turns are stacked, generating narrow parallel /(-sheets that are aligned with the... 

R. E., and Meredith, S. C. (1998). Propagating structure of Alzheimer s //-amyloid (10-35) is parallel //-sheet with residues in exact register. Proc. Natl. Acad. Sci. USA 95, 13407-13412. 

Fig. 1. Cross-/] structure of amyloid fibrils. (A) Cartoon representation of a cross-/] X-ray diffraction pattern. The defining features are a meridional reflection at 4.7 A and an equatorial reflection on the order of 10 A. The 4.7-A reflection is generally much brighter and sharper than the reflection at 10 A. (B) The cross-/] core structure of amyloid fibrils. Parallel /(-sheets are depicted, but the structure could equivalendy be composed of antiparallel /(-sheets or a mix of parallel and antiparallel. The 4.7-A spacing of /(-strands within each /(-sheet is parallel to the long fibril axis. The depicted 10-A sheet-to-sheet spacing actually ranges from about 5 to 14 A (Fandrich and Dobson, 2002), depending on the size and packing of amino acid side chains. Amyloid fibrils have diameters on the order of 100 A.

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