page_title: Beta hairpin
section_title: Artificially designed beta-hairpin
hierarchical_section_title: Beta hairpin / Artificially designed beta-hairpin
caption_attribution_description: English: azobenzene hairpin
context_page_description: The beta hairpin is a simple protein structural motif involving two beta strands that look like a hairpin. The motif consists of two strands that are adjacent in primary structure, oriented in an antiparallel direction, and linked by a short loop of two to five amino acids. Beta hairpins can occur in isolation or as part of a series of hydrogen bonded strands that collectively comprise a beta sheet.
  Researchers such as Francisco Blanco et al. have used protein NMR to show that beta-hairpins can be formed from isolated short peptides in aqueous solution, suggesting that hairpins could form nucleation sites for protein folding.
context_section_description: The design of peptides that adopt β-hairpin structure (without relying on metal binding, unusual amino acids, or disulfide crosslinks) has made significant progress and yielded insights into protein dynamics. Unlike α-helices, β-hairpins are not stabilized by a regular hydrogen bonding pattern. As a result, early attempts required at least 20–30 amino acid residues to attain stable tertiary folds of β-hairpins. However, this lower limit was reduced to 12 amino acids by the stability gains conferred by the incorporation of tryptophan-tryptophan cross-strand pairs. Two nonhydrogen-bonding tryptophan pairs have been shown to interlock in a zipper-like motif, stabilizing the β-hairpin structure while still allowing it to remain water-soluble. The NMR structure of a tryptophan zipper (trpzip) β-peptide shows the stabilizing effect of favorable interactions between adjacent indole rings.
  The synthesis of trpzip β-hairpin peptides has incorporated photoswitches that facilitate precise control over folding. Several amino acids in the turn are replaced by azobenzene, which can be induced to switch from the trans to the cis conformation by light at 360 nm. When the azobenzene moiety is in the cis conformation, the amino acid residues align correctly to adopt a β-hairpin formation. However, the trans conformation does not have proper turn geometry for the β-hairpin. This phenomenon can be used to investigate peptide conformational dynamics with femtosecond absorption spectroscopy.
caption: azobenzene hairpin
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