(a) Antiparallel Top view Side view
(b)Parallel Top view Q Side view
2.4 B turn(hairpin F turn) is also a common secondary structure found where a polypeptide chain abruptly reverses its direction 2.4.1 It often connects the ends of two adiacent segments of an antiparallel B-pleated sheet. 2.4.2 It is a tight turn of 180 degrees involving four amino acid residues 2.4.3 The essence of the structure is the hydrogen bonding between the c=o group of residue n and the nh group of the residue n+3. 2.4.4 Gly and Pro are often found in B turns. Gly is there(as the 3rd residue in type i) because it is small and flexible; for Pro it is because the peptide bond involving Pro can assume the cis configuration, which in turn generates a tight turn on the polypeptide chain 2.4.5 B turns are often found near the surface of a protein
2.4 b turn (hairpin发卡 turn) is also a common secondary structure found where a polypeptide chain abruptly reverses its direction. 2.4.1 It often connects the ends of two adjacent segments of an antiparallel b-pleated sheet. 2.4.2 It is a tight turn of ~180 degrees involving four amino acid residues. 2.4.3 The essence of the structure is the hydrogen bonding between the C=O group of residue n and the NH group of the residue n+3. 2.4.4 Gly and Pro are often found in b turns. Gly is there (as the 3rd residue in type II) because it is small and flexible; for Pro it is because the peptide bond involving Pro can assume the cis configuration, which in turn generates a tight turn on the polypeptide chain. 2.4.5 b turns are often found near the surface of a protein
3 R 1 Type I TUrns With different phi, psi angles
With different phi, psi angles
R H R H C-N R C H H C=O C-N R trans cIs Proline isomers (b)