Protein structure beta sheet

There is a wide variety of so-called globular proteins. Many of these have alpha and beta structures imbedded within the overall globular structure. Beta sheets are often twisted or wrapped into a barrel-like structure. They contain portions that are beta sheet structures... 

Figure 2.5 Schematic illustrations of antiparallel (3 sheets. Beta sheets are the second major element of secondary structure in proteins. The (3 strands are either all antiparallel as in this figure or all parallel or mixed as illustrated in following figures, (a) The extended conformation of a (3 strand. Side chains are shown as purple circles. The orientation of the (3 strand is at right angles to those of (b) and (c). A p strand is schematically illustrated as an arrow, from N to C terminus, (bj Schematic illustration of the hydrogen bond pattern in an antiparallel p sheet. Main-chain NH and O atoms within a p sheet are hydrogen bonded to each other.

Beta strands can also combine into mixed P sheets with some P strand pairs parallel and some antiparallel. There is a strong bias against mixed P sheets only about 20% of the strands inside the p sheets of known protein structures have parallel bonding on one side and antiparallel bonding on the other. Figure 2.7 illustrates how the hydrogen bonds between the p strands are arranged in a mixed P sheet. 

Figure 2.11 Beta sheets are usuaiiy represented simply by arrows in topology diagrams that show both the direction of each (3 strand and the way the strands are connected to each other along the polypeptide chain. Such topology diagrams are here compared with more elaborate schematic diagrams for different types of (3 sheets, (a) Four strands. Antiparallel (3 sheet in one domain of the enzyme aspartate transcarbamoylase. The structure of this enzyme has been determined to 2.8 A resolution in the laboratory of William Lipscomb, Harvard University, (b) Five strands. Parallel (3 sheet in the redox protein flavodoxin, the structure of which has been determined to 1.8 A resolution in the laboratory of Martha Ludwig, University of Michigan, (c) Eight strands. Antiparallel barrel in the electron carrier plastocyanln. This Is a closed barrel where the sheet is folded such that (3 strands 2 and 8 are adjacent. The structure has been determined to 1.6 A resolution in the laboratory of Hans Freeman in Sydney, Australia. (Adapted from J. Richardson.)...

This motif is called a beta-alpha-beta motif (Figure 2.17) and is found as part of almost every protein structure that has a parallel p sheet. For example, the molecule shown in Figure 2.10b, triosephosphate isomerase, is entirely built up by repeated combinations of this motif, where two successive motifs share one p strand. Alternatively, it can be regarded as being built up from four consecutive p-a-p-a motifs. 

Figure 2.17 Two adjacent parallel p strands are usually connected by an a helix from the C-termlnus of strand 1 to the N-termlnus of strand 2. Most protein structures that contain parallel p sheets are built up from combinations of such p-a-P motifs. Beta strands are red, and a helices are yellow. Arrows represent P strands, and cylinders represent helices, (a) Schematic diagram of the path of the main chain, (b) Topological diagrams of the P-a-P motif.

The interiors of protein molecules contain mainly hydrophobic side chains. The main chain in the interior is arranged in secondary structures to neutralize its polar atoms through hydrogen bonds. There are two main types of secondary structure, a helices and p sheets. Beta sheets can have their strands parallel, antiparallel, or mixed. 

Michael reactions and, 895 Beta-keto ester, 851 alkylation of, 859-860 cyclic, 892-893 decarboxylation of, 857, 860 Michael reactions and. 895 pKd of, 852 synthesis of, 892-893 Beta-lactam antibiotics, 824-825 Beta oxidation pathway, 1133-1137 mechanism of, 1133-1136 Beta-pleated sheet (protein), 1038 molecular model of, 1039 secondary protein structure and, 1038-1039 Betaine, 720 Bextra. structure of, 544 BHA, synthesis of, 629 BHT, synthesis of. 629 Bicycloalkane. 129 Bijvoet. J. M., 299 Bimolecular, 363... 

Fig. 4.1.13 A ribbon representation of the crystal structure of recombinant acquorin molecule showing the secondary structure elements in the protein. Alpha-helices are denoted in cyan, beta-sheet in yellow, loops in magenta coelenterazine (yellow) and the side chain of tyrosine 184 are shown as stick representations. From Head et al., 2000, with permission from Macmillan Publishers.

Detailed protein structures have been reported for BPI and CETP. Given the aforementioned similarities within this gene family, these protein structures serve as a likely model for the protein structure of PLTP. CETP and BPI are elongated molecules, shaped like a boomerang. There are two domains with similar folds, and a central beta-sheet domain between these two domains. The molecules contain two lipid-binding sites, one in each domain near the interface of the barrels and the central beta-sheet. 

The essential distinction between the approaches used to formulate and evaluate proteins, compared with conventional low molecular weight drugs, lies in the need to maintain several levels of protein structure and the unique chemical and physical properties that these higher-order structures convey. Proteins are condensation polymers of amino acids, joined by peptide bonds. The levels of protein architecture are typically described in terms of the four orders of structure [23,24] depicted in Fig. 2. The primary structure refers to the sequence of amino acids and the location of any disulfide bonds. Secondary structure is derived from the steric relations of amino acid residues that are close to one another. The alpha-helix and beta-pleated sheet are examples of periodic secondary structure. Tertiary... 

McDonnell, A. V., Menke, M., Palmer, N., King, J., Cowen, L., and Berger, B. (2006). Fold recognition and accurate sequence-structure alignment of sequences directing beta-sheet proteins. Proteins 63, 976-985. 

Beta sheet a form of secondary structure in proteins. 

Secondary structure those protein structures that result from hydrogen bond formation between the amino and carbonyl groups of peptide bonds. The most important ones are the alpha helix and beta sheets. 

The alpha helix and beta sheets are two types of secondary structures exhibited by polypeptides and proteins. (Rae Dejur)... 

Protein molecules are inherently asymmetric, being composed of chiral amino-acid residues coiled into larger chiral structures such as right-handed helices or twisted beta sheets. If only one protein molecule occupies a unit cell, then the cell itself is chiral, and there are no symmetry elements. This situation is rare in most cases, the unit cell contains several identical molecules... 

Kwok, S. C., Mant, C. T., and Hodges, R. S. (2002). Importance of secondary structural specificity determinants in protein folding Insertion of a native beta-sheet sequence into an alpha-helical coiled-coil. Prot. Sci. 11, 1519-1531. 

Koch et al. [111] have discussed the use of graph theoretical techniques in an attempt to find rules to relate beta sheet topology to amino acid sequence and for the comparison of beta sheet structures. They defined a graph representation for every protein in the PDB that contains beta sheets, notations and graphic representations for sheets which described the sequential and topological neighbourhoods of the strands, and constructed tools for substructure searches of this database. 

Tertiary Structure of Proteins The tertiary structure of a protein refers to how the alpha helices and beta sheet portions of a polypeptide chain are folded into a compact or globular structure. Two-dimensional representations of the three-dimensional tertiary structures of proteins are, well, pretty two dimensional. If you want to better understand tertiary structure, you can view interactive, three-dimensional models of a large variety of proteins at the RCSB Protein Data Base at http //www.rcsb.org. 

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