Beta turns structure

Asakura, T., Ashida, J., Yamane, T., Kameda, T., Nakazawa, Y., Ohgo, K., and Komatsu, K. (2001). A repeated beta-turn structure in poly(Ala-Gly) as a model for silk I of Bombyx mod silk fibroin studied with two-dimensional spin-diffusion NMR under off magic angle spinning and rotational echo double resonance. / Mol. Biol. 306, 291-305. 

J.E. Jenkins, M.S. Creager, E.B. Butler, R.V. Lewis, J.L. Yarger, G.P. Holland, Solid-state NMR evidence for elastin-like beta-turn structure in spider dragline silk, Chem. Commun. 46 (2010) 6714-6716. 

Sun, A. Q. SaUcar, R. Sachchidanand, S. Xu, S. Zeng, L. Zhou, M. M. Suchy, F. J. 2003. A 14-amino acid sequence with a beta-turn structure is required for apical membrane sorting of the rat ileal bile acid transporter. J. Biol Chem. 278 4000-4009. 

Figure 30-3 Possible secondary structure of somatostatin with a beta turn at residues 7-10 and a disulfide bond between positions 3 and 14.

Ma, K., and Wang, K. (2003). Malleable conformation of the elastic PEVK segment of titin Non-cooperative interconversion of polyproline II helix, beta-turn and unordered structures. Biochem.J. 374, 687-695. 

A.B. Smith, W.Y. Wang, P.A. Sprengeler, R. Hirschmann, Design, synthesis, and solution structure of a pyrrolinone-based beta-turn peptidomimetic, J. Am. Chem. Soc. 2000, 122,11037-11038 A.B. 

Figure 16. Schematic of the solution NMR structure of apamin that shows the C-terminal helix and two beta-turns centered at residues 3-5 and 6-8. (Reproduced from reference 214. Copyright 1983 American Chemical Society.)...

Since this domain is conserved in several enterotoxins, one expects this 13 residue domain to be the primary reason for the toxicity of the 19-residue long protein. lETN has a simple secondary structure it has got 3 beta (/ ) turns. The /9i spans from Cys to Cys , (32 from Asn to Cys, and 02 from Cys to Cys . In addition, the crystal structure contains 5 intramolecular (i.e., within the protein) hydrogen bonds that also add to the stability of the conformation. The lETN structure is reasonably rigid (because of 3 disulfide bridges, and 5 intramolecular hydrogen bonds), making it an ideal candidate for studies by computer simulations using empirical intermolecular potentials. 

The domain of a protein is determined by its secondary structure. There are four main types of domain structures alpha-helix, beta sheet, beta-turn, and random coil. 

Several studies have confirmed that beta-amyloid peptides undergo structural transitions to form mobile oligomers that are composed of a particular aggregation-prone conformation of the peptide. Once the oligomers exceed critical size, they nucleate to form protofilaments which finally transform to crossbeta sheets or fibrils that are responsible for the formation of extracellular amyloid plaques. The tendency to form beta-strands is due to its ability to stabilize the beta-turn by a salt bridge between residues aspartic acid-23 and lysine-28 and the hydrophobic region. 

The work is still in progress. However, it seems clear that the variability in secondary structure assignments in the PDB is so great that it will probably be impossible to reproduce completely the assignments which have been made by previous workers. That said, our results to date show that it is possible to identify all of the alpha-helix and beta-strand structures with a precision of about 75% and 35% respectively the results for the 3-10 stretch and turn secondary structures are very much worse, with the precision typically being less than 20%. Full details of this work will be reported elsewhere. 

Alzheimer s Disease. Figure 1 A(3 monomers can self-associate to form dimers, trimers and higher oligomers. Globular structures of synthetic A(342 are known as A(3-derived diffusible ligands (ADDLs) (3-12-mers of A(3). These structures are similar to the smallest protofibrils and represent the earliest macromolecular assembly of synthetic A(3. The characteristic amyloid fiber exhibits a high beta-sheet content and is derived in vitro by a nucleation-dependent self-association and an associated conformational transition from random to beta-sheet conformation of the A(3 molecule. Intermediate protofibrils in turn self-associate to form mature fibers. 

Starting from the protein sequence (primary structure) several algorithms can be used to analyze the primary structure and to predict secondary structural elements like beta-strands, turns, and helices. The first algorithms from Chou and Fasman occurred already in 1978. The latest algorithms find e.g., that predictions of transmembrane... 

In this review, NMR analysis of the denatured state of staphylococcal nuclease is briefly reviewed in nontechnical language. Most of the work has come from the author s laboratory over the past eight years. The initial experiments, which only measure local structural parameters, reported small amounts of persisting helical structure, two turns, and indirect evidence for perhaps a three-strand beta meander. When applied to the denatured state in 6 M urea, the same experiments indicated that most of these features are lost. 

Fig. 1. Schematic diagram of nuclease A131A in the folded conformation. The alpha helices and beta strands are labeled. NMR analysis suggests the two turns and one helix in black are modestly populated in the denatured state, whereas the shaded helix is slightly populated. Strands / l-/ 2-/ 3 form an extended structure about which littie is known. Reproduced from Barron, L. D., Hecht, L., Blanch, E. W., and Bell, A. F. (2000). Prog. Biophys. Mol Chem. 73, 1-49. 2000, with permission from Elsevier Science.

There are two allotropes of tin. One is known as gray or alpha (a) tin, which is not very stable. The other is known as white tin or beta ((3), which is the most common allotrope. The two forms (allotropes) of tin are dependent on temperature and crystalline structure. White tin is stable at about 13.2°C. Below this temperature, it turns into the unstable gray alpha form. There is also a lesser-known third allotrope of tin called brittle tin, which exists above 161°C. Its name is derived from its main property. 

White phosphorus has a white waxy appearance that turns slightly yellow with age and impurities. There are two allotropic forms of white phosphorus. The alpha (a) form has a cubic crystal structure, and the beta (P) form has a hexagonal crystalline structure. White phosphorus is extremely reactive and will spontaneously burst into flame when exposed to air at a temperature of about 35°C. It must be kept under water. But this property of spontaneous combustion has made it useful for military applications. 

Fig. 6. Deconvolved amide F region FTIR spectra of apo- and heme-hemopexin. The amide F FTIR spectra of apo- and heme-hemopexin in D2 O were recorded and curve-fitted to resolve the individual bands. The differences between the original and fitted curves are shown in the upper traces in the panels. The estimated helix (15%), beta (54%), turn (19%), and coil (12%) content of the apo-protein are not significantly changed upon heme binding 104). This analysis was required because of the positive 231-nm elhpticity band in hemopexin and is consistent with the derived crystal structure results.

---