Structure, three-dimensional hairpin loop

Figure S.2 Schematic and topological diagrams of an up-and-down fi barrel. The eight p strands are all antiparallel to each other and are connected by hairpin loops. Beta strands that are adjacent in the amino acid sequence are also adjacent in the three-dimensional structure of up-and-down barrels.

Certain RNAs also possess substantial amounts of tertiary structure. Tertiary structure in RNA refers to the folding of secondary structural elements, such as double helical regions or hairpin stem-loops, into discrete three-dimensional structures. Forces involved in stabilizing such interactions are diverse, involving hydrogen-bonding, base... 

There is a natural hierarchy in proteins (see Figure 15.1) which allows the complex three-dimensional structure to be simplified and categorized as combinations of smaller motifs. At the atom level there are patterns of side-chain interactions at the backbone level we see formation of secondary structure (a helix, P sheet and yS turn) and loop families these combine to give supersecondary structures (e.g. P hairpins) and motifs (e.g. Greek key) and ultimately the whole tertiary and quaternary structure. In this chapter we present an overview of current patterns which are observed... 

Lysozymes secondary structure includes a-helices at residues 5—15, 24—34, and 88—96 j8-sheet involving residues 41—45 and 50—54 and a hairpin turn at residues 46—49. The remaining polypeptide segments of lysozyme have coil or loop formations. Glu-35 and Asp-52 are the amino acid residues direcdy involved in the hydrolysis reaction catalyzed by lysozyme. A three-dimensional structure of lysozyme is shown in Fig. 24.15. The amino acid residues responsible for its catalytic activity are highhghted in ball-and-stick format (Glu-35 and Asp-52 to the left). 

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